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.
`
`Page 1 of 16
`
`FORD 1119
`
`Page 1 of 16
`
`FORD 1119
`
`

`

`1394
`
`G. T. ENGH AND S. WALLMAN
`
`VOL V0 L AMBDA - SOND 3Y5 TEN
`
` THREE -WAY
`
`CATAL YSY
`
`Fig.
`
`l - Volvo Lambda-50nd system
`
`LAMBDA-SOND SYSTEM.
`
`VEHICLE INSTAL LAT/0N
`
`94604; FA)” 1 55‘
`
`
`
`
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`
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`
`2 - Lambda-50nd system. Vehicle
`Fig.
`installation
`
`three major pollu-
`
`simultaneous control of all
`tants HC, C0, and NOX.
`The goal of this paper is to discuss the
`development process and the design restraints
`in the application of this three-way emission
`control system.
`
`SYSTEM APPROACH
`
`During the development of catalytic con-
`verters for exhaust gas aftertreatment it became
`evident that simultaneous conversion of all
`
`three presently regulated pollutants - hydro-
`carbons, carbon monoxide and oxides of nitrogen
`could be achieved in a single bed catalyst.
`Figure 3 shows the variation of HC, CO and N0x
`emissions from a spark ignited engine as a func—
`tion of inlet A/F (air/fuel ratio) or ‘A(lambda)
`where
`=
`actual A/F
`_
`.
`.
`F'
`)\
`equivalence ratio — steic iometric
`The solid lines show emissions before the con-
`verter, and the dotted lines after the con-
`verter. As can be seen, effective conversion
`
`Page 2 of 16
`
`three pollutants is achieved within a
`of all
`very narrow A/F ratio band around the stoichio-
`metric condition.
`injection
`Present carburetors and fuel
`systems fall short of the required A/F ratio
`accuracy. To achieve the necessary accuracy and
`speed of response in mixture preparation under
`continuous transient engine operating condi-
`tions Volvo found it necessary to enhance the
`performance of the CI fuel
`injection system by
`adding a feed back control
`loop.
`(Figures 1, 6).
`
`ALTERNATIVE SYSTEM STRATEGIES
`
`Three alternative system strategies were
`initially evaluated. Two approaches used engine
`inlet A/F ratio modulation of the exhaust gases,
`while the third approach used a generally rich
`engine A/F setting with secondary air dilution
`of the exhaust gases.
`The secondary air modulated system shown
`in figure 4 consisted of an oxygen sensor
`mounted upstream of the catalyst, a logic unit,
`
`FORD 1119
`
`Page 2 of 16
`
`FORD 1119
`
`

`

`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 stOichiometric.
`
`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.
`
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`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 TO ELECTROV/C FUEL INJECTION
`
`LAMBDA'SOAD SYSTEM WITH SECONDARY
`Alfl MODULATION
`
` ’IL’ER
`
`SEMIIYAM
`“GULJHLVE
`
`
`
`'
`
`_.
`
`EXHAUST
`GAS
`
`CATALYST
`3 WAY
`
`’ _.
`
`
`
`ELECTRONK
`
`CONTROL
`
`UMT
`
`
`Fig. 4 - Lambda-50nd system with secondary
`air modulation
`
`5 - Lambda—sond system applied to
`Fig.
`electronic fuel
`injection
`
`Page 3 of 16
`
`FORD 1119
`
`Page 3 of 16
`
`FORD 1119
`
`

`

`1396
`
`G. T. ENGH AND S. WALLMAN
`
`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-SOAD YSTEM APPLIED TO Cl FUEL
`INJEC TION
`
`
`
`Fig. 6 - Lambda-50nd system applied to CI
`fuel
`injection
`
`in figure 8, which generally follows the Nernst
`equation:
`= 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:
`1. Ability0to withstand exhaust tempera-
`tures up to 9000C continuously.
`2. Thermal shock resistance up to 5000/
`second.
`3. Mechanical vibrations in all directions
`
`of 60 g.
`4. Small characteristic changes for exhaust
`gas temperature between 350 and 800C
`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 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-
`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+- 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 12 illustrates the
`principle of this differential pressure control
`system.
`
`Table 1 Warm: guises
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`Page 4 of 16
`
`FORD 1119
`
`Page 4 of 16
`
`FORD 1119
`
`

`

`VOLVO LAMBDA-SOND SYSTEM
`
`l 397
`
`OPERATWG PRINCIPLE 0': OXYGEN SENSOR - SOND
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`Fig. 10 - Sensor signal and integrator
`characteristic
`
`INJECTION VALVE
`
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`Fig. 7 - Operating principle of oxygen sensor
`( )\-sond)
`
`OXYGEN SENSOR SIGNAL
`
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`VOLTAGE
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`1000
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`§§§§§§§
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`20O
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`CONTINUOUS FUEL
`
`INJECTION SYSTEM 82E.
`
`Fig.
`
`ll - Continuous fuel
`
`injection system BZlF
`
`0.7
`RICH.
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`0.9
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`Fig. 8 - Oxygen sensor signal
`
`ELECTRON/C LOGIC SYSTEM
`
`’
`neon/mus
`PRESSURE 3.1 up/m
`
`PRINCIPLE 0‘: FLEL SYSTEM PRESSURE REGULATON
`
`OE IEC TOR
`
`Fig. 9 - Electronic logic system
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`
`Page 5 of 16
`
`FORD 1119
`
`l2 - Principle of fuel system pressure
`Fig.
`regulation
`
`Page 5 of 16
`
`FORD 1119
`
`

`

`1398
`
`G. T. ENGH AND S. WALLMAN
`
`THE THREE-WAY 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 NOx conversion capabi-
`lities with ageing. A typical
`reducing catalyst
`promoted by ruthenium had peor HC and C0 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 AGEING TESTS
`
` til 7“ IS I’
`
`1%
`
`155
`
`”.6
`
`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-
`tions in exhaust gas composition to produce
`accelerated catalyst ageing. The test fuel con-
`tained 13 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 CO 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) 1000 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 1000 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 15.
`In addition to conversion
`
`3-MY CATALYST DETERDRATDNON 50 HR ACCELERATED
`AGEING BENCH TEST
`H
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`____ _ _ _
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`Fig. 13 - Test rig for 50 h accelerated
`catalyst ageing tests
`
`Fig. 14 — 3-way catalyst deterioration on
`50 hr accelerated ageing bench test
`
`Page 6 of 16
`
`FORD 1119
`
`Page 6 of 16
`
`FORD 1119
`
`

`

`VOLVO LAMBDA-SOND SYSTEM
`
`1399
`
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`Repeat cycle until 1000 hr test
`
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`3-way CATALYST DETER/ORAT/ON 0N 1000HR SIMULATED
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`efficiency at ideal A/F setting other factors
`such as three-way window width, and drift were
`monitored.
`Prior to and after the 1000 hour durability
`test the catalysts were CVS tested on a refer-
`ence vehicle. Results are tabulated in table 4.
`(c) EPA DURABILITY TEST was performed using
`cars to evaluate the performance of the three
`candidate catalysts under test conditions Simu-
`lating those required for the certification of
`du rabi l i ty vehicles .
`
`Vehicle
`
`
`Catalyst
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`EPA-3
`
`B
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`
`THC Pt/Rh
`0x Pt/Pd
`THC Pt/Rh
`
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`Test results are shown in figure 16.
`
`CATALYST EVALUATION TESTS performed according
`to the above procedures resulted in the follo-
`wing conclusions:
`Catalysts utilizing various noble metal
`compositions show rapid deterioration
`of N0x conversion efficiency.
`The presence of rhodium shows a Signifi-
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`Fig. 15 - 3-way catalyst deterioration on
`1000 h simulated city driving bench test
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`n
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`
`Page7of16
`
`FORD1119
`
`Fig. 16 - 3-way catalyst 50,000 mile EPA
`durability test in vehicles
`
`Page 7 of 16
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`FORD 1119
`
`

`

`1400
`
`G. T. ENGH AND S. WALLMAN
`
`improvement on three-way catalyst
`cant
`performance and ageing.
`Statutory HC and CO 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 perfonnance. 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
`caused the sensor signal at)\= l
`to increase
`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}\, so a compen-
`sating correction had to be applied to the
`regulating curve by means of a modification
`
`SHHVSIN? SflfiNAL
`
`SENSOR \OL'IRGE
`mV
`
`
`
`FINAL SENS“ FORMAT
`(IHCKER SFINEL .LAYER)
`
`
`
`————o———.— A
`new ‘— 7‘" —’ LEAN
`
`Fig.
`
`l7 — Sensor signal
`
`Page 8 of 16
`
`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
`
`1000 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 18
`shows the average life of sensors used in
`various tests.
`
`The final sensor design is shown in figure
`19. 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 engineoresulted 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.
`
`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 1119
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`Page 8 of 16
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`FORD 1119
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`

`

`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 5-10 % 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 l, 4 and 2, 3,
`as shown in figure 21. 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
`
`”new"
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`AVE/“GE SENSOR LIFE
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`Fig. 18 - Average sensor life
`
`PRODUCT/0N OXYGEN SENSOR ()— SONDZ
`
`
`
`.
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`”USO”
`55”SMMY
`ZIRCONIW
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`SNELD
`
`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 spam-i 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.
`0n 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
`
`§§N§Qfl TEMfiMTQflé 5M2 ENG/fl TQM v
`DUAL EXHAUS 7' PIPE LENGTH
`
`
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`MAX
`TEMP
`[55“) RPM)
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`160
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`
`Fig. 19 - Production oxygen sensor (}\-sond)
`
`Fig. 20 - Sensor temperature and engine torque
`versus dual exhaust pipe length
`
`Page 9 of 16
`
`FORD 1119
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`Page 9 of 16
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`FORD 1119
`
`

`

`1402
`
`G. T. ENGH AND s. WALLMAN
`
`OXYGEN SENSOR MOUNTING
`
`RELATIONSHIP BETWEEN SENSOR CLEARANQE v
`TEMPERATURE GR
`NTAND ENG!
`TOR UE
`
`IEHP. GRAD ’C/SEC
`ON INSIDE WALL AI END
`
`OF SENS“ CORE
`JD
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`180
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`Ax tom CLEARDNCE any.
`
`Fig. 21 - Oxygen sensor mounting
`
`Fig. 22 - Reiationship between sensor
`clearance versus temperature gradient and
`engine torque
`
`MOD/FICAT/ONS T0 REGULATION CURVE
`
`RICH
`
`M”)
`
`NEW REGULATION CURVE
`
`
`
`_.‘
`
`||lI|l lIIIIIL
`
`SE NSOR
`VOLTAGE
`
`THE NEW REGULATION CURVE IS MADE UP OF TWO LINESIA AND B I WITH DIFFERENT SLOPES
`
`Iv: DELAY TIME, DETERMINES THE SHIFT OF THE CENTRE LINE FROM A’ I
`IV: 0 GIVES A CENTRE LINE OF All
`
`Fig. 23 - Modifications to regulation curve
`
`Page100f16
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`FORD1119
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`Page 10 of 16
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`FORD 1119
`
`

`

`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
`3
`3
`3
`
`
`Ptth
`1921
`19:]
`5:1
`
`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
`advantage of its lower working temperature
`limit. Service interval was set at l5,000 miles
`for the EPA type durability cars.
`lOOO HOUR BENCH TEST to simulate open road
`driving and sensor and catalyst ageing was per-
`formed on the three candidate catalysts. The
`driving schedule is shown in table 5, and cata-
`lyst conversion efficiences are shown in
`figure 27.
`
`REGULATION VOLTAGE FROM COLD START
`
`us- SENSOR VOLTAGE
`u; . iNTEGRA‘IION VOLTAGE
`
`VOLVOLAMBDASONDSYSTHM
`
`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 AA
`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
`
`ffGUlAT/ON SPEED v CVS TEST EMISSIONS
`(HOT START}
`
`co
`IG/MLE)
`
`m: N0
`IG/A'HLET
`
`2.0
`
`1.5
`
`10
`
`“5
`
`0
`
`ax/sec.
`
`ans
`
`Fig. 24 - Regulation speed versus CVC test
`emissions
`
`satin mmnnmm wxmoeircvs7rsraw530N§
`(HOT START)
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`colguLE)
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`2,0
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`1.5
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`1,0
`
`«,5
`
`500
`
`SW
`
`700
`SENSOR SWITtNING WUAGE "N
`
`
`
`LIMIT FOR Au
`5,—SENs0R soNAL
`REGULATION VOLTAGE
`
` :
`
`Fig. 25 - Sensor switching voltage versus
`CVS test emissions
`
`Fig. 26 - Regulation voltage from cold start
`
`Page 11 of16
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`FORD 1119
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`Page 11 of 16
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`FORD 1119
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`

`

`1404
`
`G. T. BNGH AND S. WALLMAN
`
`EPA DURABILITY TEST was performed on three
`test cars, all
`in the 3500 lb inertia weight
`class. The engine/control system was identical
`except for the catalyst. The fuel used con-
`tained 0.02-0.03 g/gal
`lead.
`
`lalbflifidEflliliEflgflJESI
`éflflgflggilfilLflgfllilflflflg
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`Yehisle.
`EPA-4
`EPA-5
`EPA-6
`
`Estella.
`F
`G
`H
`
`The test results for the three cars are
`
`summarized in figure 28. As shown all three
`completed the 50,000 mile test. No unscheduled
`maintenance to the engine/emission control sys-
`tem was required. All sensors used completed
`their l5,000 mile durability requirements
`without problems.
`Regarding emission performance only cata-
`lyst H with the 5:1 Pt:Rh composition met the
`proposed l977 California standards. The degra-
`dation of the l9:l Pt:Rh catalysts was mainly
`due to deterioration in stoichiometric N0x
`conversion efficiency, resulting in a decrease
`in the three-way operating window with ageing.
`TAXI DURABILITY TEST was used to evaluate
`the durability performance in "stop and go"
`traffic. Three durability vehicles completed
`50,000 miles. The engine/emission control sys-
`tems were identical except for the catalyst
`used.
`
`Car
`*.
`l
`TaXi
`Taxi 2
`Taxi 3
`
`
`Catalyst
`'—
`F
`G
`H
`
`The results are shown in figure 29 and
`follow the general
`trend of previous tests.
`HIGH SPEED DURABILITY TEST was run to
`
`evaluate durability performance under heavy
`load, high speed driving conditions, utilizing
`tire test cars. All
`three vehicles had identi-
`
`cal control systems, except for the catalysts,
`and completed 50,000 miles.
`
`Table 5 - mm“ m- _(._a_t_.i_l1s_tv Ageing >Be_nm Test
`'S‘miulo:tié_d_flpe_n_ Road—Eivig f 1919
`
`
`
`0
`2m
`4m
`an
`no
`man
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`Fig' 27 ' 1000 h catalyst bench test
`Simulated open roa
`riv ng
`
`50000 MILE EPA DURABILITY TEST 07v VEHICLES
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