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 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 performance is the Volvo Lambda-sond
`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 T977 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 (}\= 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 B21 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 N0x, 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-‘I36X/78/8602-1 393302.50
`
`Copyright © 1978 Society of Automotive Engineers, Inc.
`
`1 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 2 of 16
`
`2 of 16
`
`FORD 1377
`
`

`
`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 fueli
`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.
`(I)
`(2)*
`
`*Numbers in parentheses designate References
`at end of paper.
`
`EXHAUST EMISSIONS wnn 34-IAY CATALYST
`
`Catalyst
`Opera ing
`Hin
`».
`
`.____.
`_ _ _
`
`Emissions before catalyst
`Emissions after 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
`
`SECONDARY AIR
`REGULVALVE
`
`4ATALYSY
`
`EXHAUST
`GAS
`
`‘WW meme 1-1 W“ -
`METER
`; CATALYST
`‘ A A ‘
`A—SENSOR
`IIIIIII
`INJECTION
`
`FUEL
`QUANTITY
`
`AIR
`QUANTITY
`
`ELECTRONIC
`CONTROL
`UNIT
`
`Fig. 4 - Lambda-sond system with secondary
`air modulation
`
`5 - Lambda-sond system applied to
`Fig.
`electronic fuel
`injection
`
`3 of 16
`
`FORD 1377
`
`

`
`Page 4 of 16
`
`4 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`Page 5 of 16
`
`5 of 16
`
`FORD 1377
`
`

`
`
`
`Page 6 of 16
`
`6 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 7 of 16
`
`7 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 8 of 16
`
`8 of 16
`
`FORD 1377
`
`

`
` 9 of 16
`
`9 of 16
`
`FORD 1377
`
`

`
` 10 of 16
`
`10 of 16
`
`FORD 1377
`
`

`
` 11 of 16
`
`11 of 16
`
`FORD 1377
`
`

`
`Page 12 of 16
`
`12 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
` 13 of 16
`
`13 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
` 14 of 16
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`14 of 16
`
`FORD 1377
`
`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
` 15 of 16
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`15 of 16
`
`FORD 1377
`
`

`
` 16 of 16
`
`16 of 16
`
`FORD 1377