Lambda Measurement With Pressure Compensation

29L A M B D A M E A S U R E M E N T AT T H E T E S T B E N C H

Accurate lambda measurement isa key factor in minimizing vehicleemissions and has a strong impact onfuel consumption. When measuringlambda reference values, a variety ofparameters need to be considered:■ Lambda characteristics of various

fuel types, such as diesel, gasoline,or ethanol

■ Temperature conditions duringsummer or winter testing

■ Atmospheric pressure during alti-tude testing

■ Dynamic pressure in the exhaustsystem

A lambda meter must be flexibleenough to adapt to different testingconditions and existing tool environ-ments.

Exhaust pressureLambda sensors are dependent onatmospheric pressure as well as dy-namic pressure in the exhaust system(exhaust pressure). The pressure dependence stronglyvaries at extreme richness values.

By Matthieu Bourrat and Pascal Dorlhene, Renault S.A.S; Abbo Mohamadou, ETAS

Renault adopts ES635 Lambda Module

Renault has adopted the ES635 Lambda Module as the standard device for lambda measurements. The module has

recently been deployed on the new test benches of the company’s technological innovation initiative “Pôle Innovation

Mécanique” (PIM). All of Renault’s technical centers in France and abroad are participating in the program, with the

declared objective of making Renault a leader in CO2 reduction.

28 I N T E G R AT E D T O O L C H A I N

is time-consuming as a rule. In addi-tion to the virtual prototyping on thePC, INTECRIO supports numerouspieces of rapid prototyping hardware,such as the ETAS ES1000 and ES900series. The result is the easy migrationfrom virtual prototyping on the PCto rapid prototyping onboard thevehicle.

Testing environmentWhenever code analysis is required,AVL S&F deploys the Parasoft®

C++test™ C code tester. It is suitedto static and dynamic code checks.The same tool can also be used forchecking the code that is automati-cally generated by ASCET, TargetLink,and Embedded Coder.At AVL S&F, the preferred test auto-mation tool is LABCAR-AUTO-MATION by ETAS – an open and tool-independent platform for the config-uration and execution of automatictests ranging from MiL through HiL.LABCAR-AUTOMATION – instead ofbeing limited to interaction with theETAS tools INTECRIO, INCA, and the

ETAS HiL system LABCAR – supportsall current testing and rapid proto-typing systems, such as dSPACE HiLsystems, dSPACE Autobox, ODX-LINK,NI TestStand, as well as customer-specific solutions.Test case coding in LABCAR-AUTOMATION can be accomplishedvisually by means of the AutomationSequence Builder, and/or in any ofthe languages of the Microsoft .NETFramework. This is where AVL S&F C#comes in. The test scripts can be ex-ecuted and reused in all testing en-vironments as MiL, SiL, or HiL tests.The fact that the functional MiL, SiL,and HiL tests can be configured andexecuted in a standardized user en-vironment makes the task at handdecidedly easier. The structure ofLABCAR-AUTOMATION’s Test Man-ager and Test Handler enables evenunskilled users to run preconfiguredtests.

Test documentationThe standardized documentation oftest results provides the basis for

the systematic documentation of allcompleted tests. The tool-aided eval-uation routines allow a faster andmore accurate test result analysis.The automated document generationis also a time saver. And yet, all ofthe standardization features notwith-standing, there is an efficient meansof adapting test reports to accommo-date customer requirements. In anutshell, LABCAR-AUTOMATION in-creased test documentation qualityand efficiency.

In summaryEngineers at AVL S&F have succeededin assembling an efficient and stan-dardized tool chain. The entire effort was greatly facilitat-ed by the openness of the ETAS toolsinvolved. The benefits are glaringlyevident: Test cases can be deployed withoutbeing limited by the boundaries ofdevelopment phases and projects.The deployment of this new toolchain results in concrete time savingsin concert with increases in quality.

Simulink®

TargetLink

ASCET

C Code

TargetLink

ASCET

C Code

Embedded Coder

LABCAR-AUTOMATION

C++testTM

INTECRIO

RPT

DTS

INCA

HiL

Physical Model

Integration TestFixed Point Model

Build ProcessUnit Test

System Test

ES1000

LABCAR and others

(e.g., dSPACE)

ES910

Testing environment for function development from model to production code, based on the Lifecycle Process Model (V-Model).

A pressure variation of 400 millibarin the engine’s exhaust pipe causesa 10 percent deviation of the sensorpumping current from which thelambda value is derived.

ES635 evaluationIn addition to the dependence onatmospheric pressure, the ES635Lambda Module also compensatesthe influence of exhaust pressure.

Therefore, ETAS implemented theexhaust pressure compensation (EPC)in accordance with Renault specifi-cations. The EPC algorithm considersrelevant thermodynamic and diffu-sion parameters. It is based on empir-ical results and experience accumu-lated by Renault over many years.

The ES635/EPC validation at Renault’stechnical center in Lardy included thefollowing tests:■ 1/λ measurement with synthetic gas

mixtures in a range from 0.1 (lean)to 1.2 (rich)

■ In-vehicle tests with gasoline andE85 fuels

■ Stationary and transient tests at thediesel engine test bench

■ Cold chamber tests at temperaturesof -20 °C

After all of the test data had beencompiled, it was obvious that theES635 offers several improvements.Without the EPC, the maximum erroron measured richness values reached60 percent whereas, with the EPCactivated, only a 10 percent errorwas noticed even in the worst case.Measurements of richness over time,taken in the cold chamber on the en-gine test bench at -20 °C, showedthat the time resolution of the ES635module is high enough for estimatingengine speed.

While ES635 data was always veryclose to the richness values set bythe test bench (which was proventhrough the use of synthetic gas),a small deviation compared to thein-house lambda meter was noticedin one test configuration. The devi-ation might have been caused due tothe fact that the pressure correctionfactor of the ES635 EPC was con-stant, and that the lambda curve usedby the ES635 was the default one.

As an immediate reaction, ETAS de-livered a new firmware version toRenault to provide for pressure factoradaptation.

Further tests with fine-tuned lambdacurves and an optimized pressurefactor are planned by Renault engi-neers.

Summary The ES635 Lambda Module fromETAS provides a robust, open, flexible,and future-proof solution. Capableof standalone operation, the moduleprovides an easy-to-use configurationtool. It is INCA-compliant and offersan open XCP interface to existingapplications. In addition to defaultcharacteristics suitable for basic ap-plication, it supports Renault’s spe-cific lambda curves. The modulesupports the relevant Bosch lambdasensors and enables Renault tomigrate from the LSU4.9 to thelatest LSU ADV sensors. The ES635 complies with Renault’sprocesses, methods, and tools. Dueto its high-quality exhaust pressurecompensation, the ES635 module isable to replace the in-house lambdameters at Renault.

30 L A M B D A M E A S U R E M E N T AT T H E T E S T B E N C H 31L A M B D A M E A S U R E M E N T AT T H E T E S T B E N C H

Richness of a synthetic gas measuredby the ES635 module with exhaustpressure compensation (red triangles).The diagonal indicates the set valuesmeasured by a gas analyzer. The ES635 measurements deviate from the set values by a maximum of 1.8 percent.

Graphic showing the impact of the EPC exhaust pressure compensation on the richness measurement. The richness was set to a constant value on the test system, while thepressure was varied (red curve). On the ES635 module, the EPC was alternately activated and deactivated.With EPC off, richness measurements(blue curve) vary significantly and –as expected – in the opposite directionof the measured pressure changes(red curve). With EPC active, the mea-sured richness values vary only slightlyin response to changes in exhaust pressure.

THE CHALLENGEBecause of the direct influence of lambda values on emissions and fuel consumption, engine development and ECU calibration requires accurate lambda measurements.

THE SOLUTIONThe ES635 Lambda Module compensates the exhaust pressure effect on lambda measurements, which results in significant accuracy gains (factor 6).

THE BENEF ITBy leveraging the know-how of Renault on exhaust pressure compensation, the ES635 module can replace Renault’s current in-house lambda meter solution.

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