770295
`
`Development of the Volvo
`Lambda-Sond 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 promisi ng
`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 simul taneously exhibits
`excellent exhaust emiss ion control and fuel eco(cid:173)
`nomy performance is the Volvo Lambda-sond
`system. The system utilizes a "three-way" cata(cid:173)
`lytic converter, and an additional closed loop
`to the fuel injection system to provide feed(cid:173)
`back· control of the inlet air/fuel ratio.
`
`DESCRIPT ION OF PRODUCTION SYSTEM
`
`Vol vo has developed a three-way emiss ion
`cont rol system for its 2.1 litre 4 cyl i nder
`engine to meet the 1977 California exhaust emis(cid:173)
`sion requirements. In addition to excel lent
`exhaust emission characteristics, the system
`has demonstrated good fuel economy and drive(cid:173)
`abil i ty compared with alternati ve control
`syst ems.
`
`The Volvo application utilizes a feed-back
`control loop added to the normal CI (continuous
`injection) fuel injection system, and a "three(cid:173)
`way" catalyst, as shown schematically i n figure
`1. Figure 2 shows the positions of major compo(cid:173)
`nents in relation to the engine.
`An oxygen sensor, situated at the exhaust
`manifold outl et, can detect the momentary oxy(cid:173)
`gen level i n the exhaust gas, which is an in(cid:173)
`dicat ion of whether t he inlet A/ F ratio is
`leaner or richer than sto ichi ometric ( A= l).
`The sensor transmits a continuous non- linear
`el ectrical signa l to the electronic control
`module which converts it into a control signal
`for the continuously oscillating on/off fre(cid:173)
`quency valve. When the on/of f bias time is
`al tered the frequency valve raises or lowers
`the different ial pressure over the metering
`slots i n the fuel distributor, providing accu(cid:173)
`rate and continuous control of the quantity of
`fuel injected.
`The resulting accuracy and speed of re(cid:173)
`sponse in mixture preparation, even under
`transient conditions . (as in traffic driving),
`ensures that the exhaust gas fed to the cata(cid:173)
`lyst is always within the very narrow compo(cid:173)
`sition band which enables the catalyst to ope(cid:173)
`rate in the "three-way" manner, thus achieving
`
`Volvo has developed the first production
`emission control system to fu lly utilize a
`three-way catalyst. Called the "Vol vo Lambda(cid:173)
`sond system", it is applied to the 4- cylinder
`t'n-li ne 821 engine, and employs three essential
`new components - an exhaust gas composition
`sensor, an additional feed-back loop to the con(cid:173)
`tinuous fuel injection system, and the catalyst.
`1393
`0096· 736XnB/8602-1393$02.50
`Copyright © 1978 Society of Automotive Engineers, Inc.
`
`Outstand ing certification resu lts were achieved,
`especially for NOx, combined with good drive(cid:173)
`ability, power output, and fuel economy. The
`development and performance of the system, and
`the test procedures used, are described in de(cid:173)
`tail, and its future potential and limitations
`are discussed.
`
`BMW1079
`Page 1 of 16
`
`

`

`
`
`1394
`
`
`
`
`GXRENGHANDS.WALUMAN
`
`
`
`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 INSTAL LAT/ON
`FOS. VAC
`.\.){. \/
`
`
`
`
`ENG/NE FAMILY LCL
`
`.7. A-sozvo
`L
`FREOUENCY VALVE
`5. cowmm mm
`
`
`
`
`
`
`
`
`
`2 - Lambda-sond system. Vehicle
`Fig.
`installation
`
`
`
`
`
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`
`
`
`
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`
`
`
`
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`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.
`
`
`
`
`
`
`
`
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`
`
`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-
`
`
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`
`
`
`tions Volvo found it necessary to enhance the
`
`
`
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`
`
`
`
`
`
`
`
`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.
`
`
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`
`
`
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`
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`The solid lines show emissions before the con-
`
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`
`
`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,
`BMW1079
`Page 2 of 16
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`Page 2 of 16
`
`BMW1079
`Page 2 of 16
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`

`

`VOLVO LAMBDA-SOND SYSTEM
`
`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 continu.ously corrected the injector open(cid:173)
`ing duration to obtain stoichiometric A/F ratio.
`(l) (2)*
`
`*Numbers in parentheses designate References
`at end of paper.
`
`EXHAUST EMISSIONS WITH 3-WAY CATALYST
`
`co
`
`"°"
`
`HC
`
`6'.85 ~,9J['~ i~1
`
`b~7
`
`. - - -~ -
`
`i\5 ;;3:: At R
`
`Equivalence Rotio
`
`Catalyst
`Operotimiil
`Windo..,
`
`Elllissions before cctolyst
`
`E•issions ofter cotolyat
`
`Fig. 3 - Exhaust emissions with 3-way catalyst
`
`LAMBDA·SOND SYSTEM WITH SECONDARY
`AIR MODULATION
`
`1395
`
`The mechanical fuel injection three-way
`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(cid:173)
`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(cid:173)
`tibility with present production engine and
`fuel systems. These factors affecting these(cid:173)
`lection of a candidate system for further deve(cid:173)
`lopment are summarized in table 1. The secondary
`air modulated system was abandoned mainly be(cid:173)
`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(cid:173)
`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(cid:173)
`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. These(cid:173)
`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(cid:173)
`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
`
`LAMBDA-SOND SYSTEM APPLIED TO ELECTRONIC FUEL INJECTION
`
`EXHAUST
`GAS
`
`ENGINE
`
`A-SENSOR
`
`FUEL
`QUANTITY
`
`AIR
`QUANTITY
`
`ELECTRONIC
`CONTROL
`UNIT
`
`Fig. 4 - Lambda-sond system with secondary
`air modulation
`
`Fig. 5 - Lambda-sond system applied to
`electronic fuel injection
`
`BMW1079
`Page 3 of 16
`
`

`

`1396
`
`mass production, g1v1ng 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(cid:173)
`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(cid:173)
`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 100 millivolts under lean condi(cid:173)
`tions. This produces an on-off type of signal
`around stoichiometric A/F conditions, as shown
`
`LAMBDA-SOND SYSTEM APPLIED TO Cl FUEL
`INJECTION
`
`AR
`
`·SENSOR
`SIGNAL
`
`Fig. 6 - Lambda-sond system applied to CI
`fuel injection
`
`G. T. ENGH ANDS. WALLMAN
`
`in figure 8, which generally follows the Nernst
`equation:
`E = RT/K ln (Pl/P2)
`where Eis the sensor signal in millivolts
`Risa thermodynamic constant
`Tis absolute temperature
`K is the efficiency factor
`Pl is partial pressure of ambient oxygen
`P2 is partial pressure of exhaust gas
`oxygen
`After initial evaluation, the following
`design requirements for the oxygen sensor were
`found:
`1. Ability to withstand exhaust tempera(cid:173)
`tures up to 90o0 c continuously.
`2. Thermal shock resistance up to 5o0c;
`second.
`3. Mechanical vibrations in all directions
`of 60 g.
`4. Small characteristic change~ for exhaust
`gas temperature between 350 and 800 C.
`5. Stable characteristic with ageing.
`THE ELECTRONIC LOGIC SYSTEM is shown sche(cid:173)
`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 10 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(cid:173)
`rects the fuel flow by influencing the pressure
`drop over the fuel flow metering slots in the
`fuel distributor. The CI system itself (figure
`11) is capable of controlling the A/F ratio
`within± 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(cid:173)
`tial pressure over the fuel flow metering slots
`(which is normally kept constant in the CI sys(cid:173)
`tem) offered a faster response time and extended
`control range, thus allowing full high altitude
`compensation on the lean side, without the addi(cid:173)
`tion of extra parts. Figure 12 illustrates the
`principle of this differential pressure coRtrol
`system.
`
`Table 1 Prototype_systems - selection_for_ further develooment
`
`'
`
`Altitude
`conmensa ti on
`
`Orive-
`ability
`
`1;eiqht
`
`i Comratibi-
`;
`· l i t_y present :
`product
`
`Notes
`
`-·
`
`..
`
`limited
`
`; good
`
`: fair
`
`good
`
`good
`
`yes
`
`exce 11 ent I yes
`
`I
`
`I fair
`
`I ~.ood
`
`i
`
`! good
`i
`I good
`
`: poor
`
`good
`
`: Can be used
`with car-
`buretors
`No mechanical
`regulation
`system required
`
`Fuel
`economy
`
`poor
`
`System
`
`Oxygen sensor
`Air pump module
`
`Oxygen sensor
`Electronic fuel• -
`injection
`Oxygen sensor
`Mechanical fuel
`injection
`
`.Emissions
`co
`!IC
`tlOx
`CVS q/mile
`
`. 0.216
`
`12.0
`i
`!
`0. 2 ! 2. 5 : 0.4
`I
`i
`I
`I
`0.212. 5 0.4
`
`i
`
`*Development standard in the middle of 1973
`
`Page 4 of 16
`
`BMW1079
`Page 4 of 16
`
`

`

`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
`
`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
`
`BMW1079
`
`Page 5 of 16
`
`
`
`TRIANGULAR
`POWER STAGE COMPARAIDR
`WAVE
`
`
`GENERATOR
` FREQUENCY
`VALVE
`
`
`
`
`
`)\- SENSOR COMPARAIOR
`
`
`SENSOR
`
`SIGNAL
`DE TECTOR
`
`
`Fig. 9 - EIectronic Iogic system
`
`SEN50R
`VOLTAGE
`
`EMK
`ImV I
`1000
`
`900
`
`500
`
`700
`
`600
`
`500
`
`£00
`
`300
`
`200
`
`100
`
`BMW1079
`Page 5 of 16
`
`

`

`1398
`
`G. T. ENGH ANDS. WALLMAN
`
`THE THREE-WAY CATALYST is mounted down(cid:173)
`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(cid:173)
`lysts of the platinum/palladium type were used.
`This type of catalyst showed good virgin three(cid:173)
`way conversion characteristics, but suffered
`rapid deterioration of NOx conversion capabi(cid:173)
`lities with ageing. A typical reducing catalyst
`promoted by ruthenium had poor HC and CO capa(cid:173)
`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 AGEiNG TESTS
`
`gas was supplied from a 2 litre engine running
`at 3000 rpm and 100 Nm (3/4 load). The inlet
`A/F ratio alternated between 13.6 and 15.5 at
`90 second intervals to provide the rapid varia(cid:173)
`tions in exhaust gas composition to produce
`accelerated catalyst ageing. The test fuel con(cid:173)
`tained 13 ppm lead and 300 ppm sulphur. Exhaust
`gas 0temperature 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 CO and NOx are simultaneously converted
`with high efficiency. Deterioration curves are
`shown in figure 14.
`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(cid:173)
`cated that platinum/rhodium catalysts are
`superior to normal oxidation catalysts in
`three-way conversion durability performance.
`(b) 1000 HOUR SIMULATED CITY DRIVING
`AGEING TEST ,vas performed using a programmed
`engine dynamometer. The engine was operated
`according to the city driving cycle tabulated
`in table 3. The 1000 h test simulated approxi(cid:173)
`mately 30,000 miles of vehicle driving. Pro(cid:173)
`mising catalyst candidates were selected from
`the results of the 50 hour ageing cycle. Con(cid:173)
`version efficiency of the catalyst was measured
`at 200 hour intervals. Average conversion effi(cid:173)
`ciency of the catalyst throughout the test is
`shown in figure 15. In addition to conversion
`
`3-WAY CATAIYST DETERIORATION ON 50 HR ACCELERATED
`AGEING BENCH TEST
`
`- - - - - -
`- - · - · -
`- - - - - - -
`- - - - - - -
`
`CAT. A
`CAT_ B
`CAl C
`CAT. 0
`CAT. e
`
`Ox
`pt
`TWC Pt/Rh
`pt/ Rh
`TWC
`pt/ Pd
`Ox
`rwc
`pt / Rh
`
`.. ______ -- -
`
`100 , - - - - - - - - - -
`'/.
`
`-··-·-
`
`C.,OALYST
`
`15,5
`
`13,6
`
`3
`
`6
`
`TIHE(MIN/
`
`Fig. 13 - Test rig for 50 h accelerated
`catalyst ageing tests
`
`Page 6 of 16
`
`50 t-----,.----.--..-----,.--
`0
`20
`40
`SOh Test time
`'O
`
`co
`
`100 . . - - - - - - - - - -
`'/,
`
`-------.. - -
`' ----, -- ----------
`'
`'-----------------------
`50 -!-------.---.---..----.--
`m
`,o
`0
`~h
`~
`~
`
`l l l l r - - - - - - - - -
`"/,
`
`- - ---.. -.. _ .. _,,_
`.. "'"' .. -------=-=-----=
`.... _
`"'-----------------------
`
`HC
`
`50 t----.--.---..-----
`0
`
`Fig. 14 - 3-way catalyst deterioration on
`50 hr accelerated ageing bench test
`
`BMW1079
`Page 6 of 16
`
`

`

`
`
`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_Vs._.LL_W_
`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 [Humnrv '
`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
`‘
`
`
`
`I
`
`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
`
`Page 7 of 16
`
`IO
`
`20
`
`1)
`
`£0
`
`50
`
`111000 MILES
`
`Fig. 16 — 3-way cataIyst 50,000 miIe EPA
`durabiTity test in vehicIes
`
`BMW1079
`
`Page 7 of 16
`
`BMW1079
`Page 7 of 16
`
`

`

`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
`(1HlCKER SPINEL .LAYER)
`
`
`\\
`EARLIER SEN£R\
`
`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.
`
`
`
`.......................l”
`
`llll
`
`lil
`
`._.-..._~..........
`
`100
`
`500
`
`RICH .‘_
`
`7‘“ _. LEAN
`
`Fig.
`
`l7 - Sensor signal
`
`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
`BMW1079
`Page 8 of 16
`
`Page 8 of 16
`
`BMW1079
`Page 8 of 16
`
`

`

`VOLVO LAMBDA-SOND SYSTEM
`
`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(cid:173)
`quirements were only achieved with the dual
`pipe length less than 200 mm. Here 5-10 % 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 1, 4 and 2, 3,
`as shown in figure 21. Initial testing with
`the window mounting revealed several sensor
`thennal 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(cid:173)
`tial between the two exhaust pipes at the sen(cid:173)
`sor mounting is critical. Incr~asing the window
`
`Ol.RABIUTV
`VEHICLE
`TEST BENCH
`(1000mi)
`(HOURS)
`
`50
`
`45
`
`40
`
`35
`
`AVERAGE SENSOR LIFE
`
`OK
`
`30 1000 OK
`
`OK
`
`OK
`
`25
`
`20
`
`15 500
`
`F41l
`
`FAIL
`
`FAIL
`
`OK
`
`OK
`
`OK
`
`10
`
`~~~~~
`
`1000h BENCH 1000h BENCH HWY
`CITY
`
`TAXI FLEET
`
`HIGH SPEED
`
`EPA DURABILITY
`
`1401
`
`to allow some bypass solved the problem but
`reduced the engine power performance forcer(cid:173)
`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(cid:173)
`tem remains approximately constant, the total
`response time of the system is detennined 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(cid:173)
`lation speed to be used, as shown by the thin
`line in figure 23 labelled "earlier regulation
`curve". The r~lationihip between the regulation
`speed and exhaust emissions during CVS testing
`is shown in figure 24.
`Durability testing then revealed that al(cid:173)
`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 ENGINE TORQUE v
`DUAL EXHAUST PIPE LENGTH
`
`MAX
`lllRWE
`f4SOORPMI
`
`1tlO
`
`150
`
`140
`
`MAX
`TEMP
`{4500RPM)
`
`900
`
`800
`
`,oo
`
`100 200
`
`31111 &00 500 IIOO 100 1110 JIJO
`a.JAL PIPE LENGTH mm
`
`SENSOR IDLE TEMP.. 715 nwn DUAL PIPE , 235 'c
`290nwn DUAL PIPE : 340 ·•c
`
`SENSOR MOUNTED AT EXHAUST MANIRlUJ OUTLET, 420 'C
`
`CA •
`
`ZIRCONIUM DIOXIDE SENSOR
`
`CALCIUM STABILIZED
`
`YTTRIUM STABILIZED
`
`FIRST GENERATION
`
`FINAL FORMAT
`
`Fig. 18 - Average sensor life
`
`PRODUCTION OX'rGEN SENSOR ( .A- SOND J
`
`INTERNAL
`AND
`EXTERNAL
`SURFACES
`PLAllNUM
`PLATED
`
`HOUSlt«J
`
`ZIRCONIUM
`DIOXIDE
`BODY
`
`Fig. 19 - Production oxygen sensor (~-sond}
`
`Fig. 20 - Sensor temperature and engine torque
`versus dual exhau.st pipe length
`
` 9 of 16
`
`BMW1079
`Page 9 of 16
`
`

`

`1402
`
`G. T. ENGH ANDS. WALLMAN
`
`OXYGEN SENSOR MOUNTING
`
`RELATIONSHIP BETWEEN SENSOR CLEARANCE v
`TEMPERATURE GRADIENT AND ENGINE TORQUE
`
`TORQ.UE
`(Nm)
`
`TEMP. GRAD.
`' , , , ,
`..__ _________ _
`
`170
`
`160
`
`150
`
`140
`
`TEMP. GRAD. •c/SEC.
`ON INSIDE WALL AT END
`OF SENSOR CORE.
`
`30
`
`20
`
`10
`
`100
`
`2 0
`A= mm2
`
`300
`
`400
`
`CLEARANCE
`
`CRILL POINT
`ANGLE
`vV
`I.>
`
`Q
`
`0,5
`
`1,75
`
`b
`
`b
`0.75
`1
`
`1,75
`
`1
`
`·2.75
`
`6
`
`15
`
`. .
`
`V
`1eo·
`
`140•
`
`" .
`1eo• .
`
`"
`
`B
`
`A(mm1 )
`
`29
`83
`
`95
`
`107
`
`112
`
`165
`
`"'
`
`SECTION A-A
`
`A: TOTAL CLEARANCE AREA
`8: f'A)()UCTON CONFIGI..RATON
`
`Fig. 21 - Oxygen sensor mounting
`
`Fig. 22 - Relationship between sensor
`clearance versus temperature gradient and
`engine torque
`
`MODIFICATIONS TO REGULATION CURVE
`
`RICH
`
`tv{ms)
`
`NEW REGULATION CURVE
`
`VOLTAGE
`Us
`(nV)
`
`SENSOR t
`---,
`I
`I
`I
`I
`I
`
`REGUL.
`VOLT
`
`I
`I
`I
`I
`I
`lb
`
`EARLIER REGULATION CURVE
`
`i--
`I
`I
`I
`I
`I
`I
`I
`I I
`
`I
`I
`
`-
`
`'
`
`-,
`
`L_
`
`j-------:-+
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`1-t
`I
`I
`I
`I
`I
`L--
`
`I
`I
`I
`I
`I
`I
`I
`I
`-
`
`lHE NEW REGULATION CURVE IS MADE UP OF TWO LINES I A AND B l WITH DIFFERENT SLOPES
`
`tv • DELAY Tl.ME, DETER MIN.ES THE SHIFT OF THE CENTRE LINE FROM ~ • I
`tv = 0 GIVES A CENTRE LINE OF ).!"' I
`
`Fig. 23 - Modifications to regulation curve
`
` 10 of 16
`
`BMW1079
`Page 10 of 16
`
`

`

`VOLVO LAMBDA-SOND SYSTEM
`
`problem was mainly encountered at higher vol(cid:173)
`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(cid:173)
`gulation curve (thick line in figure 23) thus
`raising the average A/F ratio by the amount~),.,
`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(cid:173)
`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 obt