2008-01-0286

Setup of an Engine Rapid Control Prototyping System for
Catalyst Research and Evaluation Testing
Shugang Jiang, Michael Smith, Satoshi Furukawa and Mark Menge
A&D Technology Inc.
Copyright © 2008 SAE International

ABSTRACTINTRODUCTION

To fulfill ever increasingly stringent emission regulations,a great many studies on engine control and catalytic
converter performance have been made. Topics of greatinterest in this area, to name a few, include: therelationship between catalyst light-off time and air-fuel(A/F) ratio; the relationship between forced A/F ratio
modulation and catalyst efficiency; the effects of phaseshifted A/F ratio modulation between banks of a dualbank engine, or among cylinders of a single manifold
engine on catalyst efficiency; and methods of modelingand measuring the oxygen storage capacity of acatalytic converter by rich-lean transition, A/F ratio
sweeping, or other on-line estimation methods.

With environmental protection in the forefront of world
issues, increasingly stringent emission regulations arebeing enforced worldwide. Facing these challenging
requirements on emissions, OEMs and suppliers havebeen working in many areas of engine and vehicle
development to achieve their goals. Among these areas,
the three-way catalytic converter application is ofextraordinary importance and is an area where muchresearch and testing has been conducted. Major
activities in this area can be categorized into two groups.
The first group mainly focuses on the improvement of
converter performance through catalyst technology,
such as the development of oxygen storage material;
improvement of composition and arrangement ofprecious metals for better conversion efficiency;
optimization of the structure to create a catalyst selfregeneration function and mitigate deterioration, etc. The
second group includes various activities in engine
control, especially in A/F ratio control to increase theperformance of the catalyst [1-13].

To undertake this type of research, an engine control
system with necessary functions, especially with very
flexible A/F ratio control capabilities, is needed. Mass
production ECU does not provide the flexibility desired
and it is also hard to develop and integrate the control
algorithms needed for catalyst testing into the existing
ECU software. An engine rapid control prototyping
system is set up in an engine dynamometer test cell
environment to overcome the limitations of mass
production ECU and fulfill the requirements for catalyst
research and testing. Model-based development
methodology is adopted for the design andimplementation of necessary software. Control
algorithms, including individual bank control of a dualbank engine, A/F ratio modulation of different
frequencies and amplitudes, with and without phase shift
between banks, A/F ratio rich-lean transition andsweeping etc, are designed using graphical language,
automatically converted into executables to run on thereal-time target. UDP communication for real-timecommand and variable exchange between the engine
controller and the test cell controller is developed tofacilitate testing. The system provides the flexibility andgood control performance desired for catalyst researchand evaluation testing. Application and results of thesystem on a 4.6L V8 gasoline engine is given.

It is well known that A/F ratio has great effect on catalyst
conversion efficiency. Research topics in this area
include among others:• The influence of A/F ratio on catalyst light-off time
[1,13]• The relationship between forced A/F ratio modulation(frequency and amplitude) and catalyst conversion
efficiency [2,3,4,7,8]• The effect of phase-shifted A/F ratio modulation
between banks or among cylinders on conversion
efficiency [2,3,9]• methods of modeling and measuring the oxygenstorage capacity of a catalytic converter by rich-leantransition, A/F ratio sweeping, or other on-line
estimation mechanisms [4-7,10-12]
We will briefly review the above cases. It is reported that
operating an engine with retarded ignition timing
combined with lean A/F ratio will decrease catalyst lightoff time and consequently reduce engine emission [1]. It
is also reported that perturbing the A/F ratio to make useof the oxygen storage capacity of the catalyst yields

better conversion efficiency than just keeping theconstant stoichiometric value upstream of the converter[4]. These researches involve controlling the A/F ratio at
desired constant value or desired average value with
perturbation.
For dual bank engines, some research indicates thatindependently controlling the A/F ratio of each bank tomake their lean and rich status just opposite to eachother (called phase-shifted A/F ratio modulation) will
benefit catalyst efficiency since both rich and lean
exhaust species are present simultaneously at theconverter and provide a highly reactive mixture to thecatalyst [2,3]. It is also claimed that this mechanism will
reduce the demand on the oxygen storage capacity of
the catalyst since the exhaust from the two banks will
combine and achieve a near-stoichiometric mixture prior
to entering the converter. This research involves
individually control the fuel injection of the banks so that
their A/F ratio waveforms have the desired averagevalue, modulation frequency, perturbation amplitude andphase shift.
When carrying out measurement of the oxygen storage
capacity of the catalyst, commonly used methods
involve controlling the engine to run under certain A/F
ratio patterns and monitoring the engine and catalyst
behavior, such as studying the response delay of adownstream A/F ratio sensor when the engine is going
through rich and lean transitions, or measuring the
break-through perturbing oxygen quantity when doing
engine A/F ratio sweeping [4,5]. These cases require theA/F ratio to go through square wave, or low frequency
triangle wave superimposed with higher frequency
modulation.
We see all these studies and testing require flexible
control of A/F ratio — desired constant value, desired
average value, various modulation frequencies, desired
perturbation amplitude, and with or without phaseshifting between banks. Mass production ECU does notprovide the flexibility needed for these purposes. It is
hard to develop catalyst testing algorithms and integratethem into the existing ECU software. We set up anengine rapid control prototyping system in an engine
dynamometer test cell environment to overcome theselimitations. By the use of model-based development
methods, algorithms are specified in a high-levelgraphical language and directly compiled into
executables to run on the real-time hardware. The
engine control features stated above are easily designed
and implemented to fulfill the catalyst study and testing
requirements.
To facilitate testing, a mechanism for real-time exchangeof commands and variables between the engine
controller and the test cell controller is desired. UDP
communication is developed to fulfill this need. The test
cell controller sends commands to the engine controller
through the UDP interface so that the engine is put into
specific operating modes for testing and measurement.
Various engine operating modes are designed andimplemented to realize various A/F ratio patterns.
Engine control parameters and variables are alsotransferred to the test cell controller through UDP
communication for analysis purpose.
The system is applied to a 4.6L V8 gasoline engine.
Results of A/F ratio control for various testing needs arepresented. The application and results reflect theflexibility and good control performance of the system.
This paper is organized into the following four sections:
I. System Overview describing the overall designand configuration of the integrated system.
II. Engine Rapid Prototyping Controller Setup
describing the features of the controller, its
hardware and software configurations, and thefunction modules used for engine control.
III. Model-Based Software Development andApplication Results describing the developmentof needed engine control features, especially thealgorithms for steady state A/F ratio modulation andphase-shifting, rich-lean transition, and A/F ratio
sweeping etc. The results of application on a V8
engine are also given.
IV. Conclusion summarizing the features and theperformance of the system.
I. SYSTEM OVERVIEW
Figure 1 shows an overview of the integrated system. It
consists of a real-time test cell controller, and a rapid
prototyping engine controller. The test cell controller,
together with all the necessary signal interfaces andpower units etc, realizes real-time control of the engine
test cell environment, including the dynamometer,
engine throttle, and other accessories. It sets the engine
operation point (speed and load) and maintains theaccessories, such as coolant conditioning system, oil
conditioning system etc, in proper condition. The
controller is connected to a host PC through Ethernet forgraphical user interface (GUI).

Fig. 1 Overview of the Integrated System

The engine rapid prototyping controller, together withnecessary signal conditioning and power electronics
modules, realizes the functions necessary for engine
operation, including ignition and fuel injection. Engine
A/F ratio control algorithms for various catalyst researchand testing purposes are developed. These functions
are designed and implemented using the model-basedengineering methodology. First the control algorithms
are specified using The MathWorks products(MATLAB®/Simulink®/Stateflow®) on a host PC.
Necessary S-functions for the specific real-time
hardware target are developed and integrated in thecontrols. Then the control algorithms are converted into
C code by Real-Time Workshop®, and compiled, linked,
and downloaded to the target platform to control engine
operation. The rapid prototyping controller is connected
to a host PC through Ethernet. GUI is developed suchthat control parameters can be adjusted and engine
behavior easily monitored in real time.
Communication between the test cell controller and theengine controller can facilitate catalytic converter testing.
We realize this function through the User Datagram
Protocol (UDP) over Ethernet physical layer. UDP is a
simple message-based protocol that provides anefficient means for communicating short packets of data
between processes, avoiding the overhead of flow
control and data stream checking and correcting.
Considering the real time nature of the communication
between the engine controller and the test cell controller,
and also the limited data volume, UDP is a very suitable
solution. With this mechanism, the test cell controller
sends out mode commands requesting the engine
controller to fulfill. The engine controller receives thecommand and runs the engine in the requested mode,
fulfilling different types of catalyst evaluation testing,such as catalyst light-off, lean-rich A/F ratio transition,
A/F ratio sweeping, A/F ratio modulation, and phaseshifting etc. The engine controller also sends suchcontrol parameters as spark advance, fuel injection
width, and lambda values etc, together with othervariables indicating the engine status back to the test
cell controller for monitoring, logging and analysis
purposes.
Necessary A/F ratio sensors and thermocouples are
installed. Engine-out exhaust temperature and mass
flow entering the catalytic converter should be regulated
per the test requirements. Based on research or testingneeds, up to 4 Lambda sensors can be installed in thesystem. As shown in Figure 1 for a V8 gasoline engine,a Lambda sensor is installed at each manifold
corresponding to the left and right bank. A third sensor isinstalled upstream of the catalytic converter, after the left
and right bank manifolds merge together. A fourth one isinstalled downstream of the catalytic converter. With
such a configuration, the studies mentioned above, suchas the effect of phase shift of A/F ratio modulation on
catalyst conversion efficiency, and the measurement ofoxygen storage capacity through the response delay ofdownstream A/F ratio sensor etc, can all be performed.

II. ENGINE RAPID PROTOTYPING CONTROLLER
SETUPThe engine rapid prototyping controller together withnecessary function modules, signal conditioning andpower stage modules form the hardware platform forengine control. Figure 2 shows the hardware frameworkof the engine rapid prototyping controller [14]. It has adual CPU architecture, using a PentiumM processor for
high-speed simulation and control, and a Renesas SH4
processor for running the human-machine interface,
including color touch-screen LCD, function keys, andEthernet communication with the host PC. A bus
controller on the active back plane handles the datatransfer between the interface boards and the CPUs.
This design frees up the PentiumM CPU and enables
execution of highly efficient digital signal processing
operations. The controller has a modular design for®
function modules. Simulink S-functions to accessmodule functionalities are developed.

Fig. 2 Hardware Architecture of the Engine Rapid
Prototyping Controller
Figure 3 shows the software architecture of thecontroller and the specific role of each software
component.
MathWorks
products
MATLAB®/Simulink®/Stateflow® are used to develop
control logic in the form of model block diagrams. The Sfunctions for system hardware and function modules aredeveloped and integrated in the block diagram. RealTime Workshop® converts the block diagram into C
code, which is then compiled, linked, and downloaded
automatically to the target platform for real-time
execution under the RT-Linux operating system.
VirtualConsole software is the graphical user interface tothe controller that enables the arrangement of various
screen elements on the host PC and on the color touchscreen LCD. These screen elements are associated withthe variables or parameters of the Simulink® model,
enabling real-time parameter setting and signal
monitoring.

or without phase-shifting, rich-lean A/F ratio transition,
and A/F ratio sweeping. The idea is to control the A/F
ratio upstream of the catalyst (Lambda1 and Lambda2 in
Figure 1) to fulfill desired patterns and study theperformance of the converter and the engine under thatcondition. Below we will give more details of the design
and realization of these A/F ratio control algorithms.
Implementation and results on a V8 engine are also
given. One thing need be pointed out is that how thedownstream sensors (Lambda3 and Lambda4 in Figure1) react to the A/F ratio patterns is not the major topic of
this paper and therefore will not be covered.

Fig. 3 Specific Roles of the Rapid Prototyping
Controller Software Components
To perform engine control for the catalyst research andtesting purpose, two function modules are integrated in
the controller: a general purpose A/D input board, andan engine timing detection and control board. The
analog input board is used for measuring such variables
as throttle position, manifold absolute pressure, intake
mass air flow rate, intake air temperature, and engine
coolant temperature, etc. It is also used to measure theA/F ratio, which are analog signals from A/F ratio
meters. The engine timing detection and control board isused for processing the crankshaft and camshaft input
signals, obtaining engine speed and timing, as well as
sending out control commands for ignition and fuelinjection. Necessary signal conditioning modules, as wellas power electronics modules with proper functions for
actuator operation are also developed and integrated in
the system.
III. MODEL-BASED SOFTWARE
AND APPLICATION RESULTS

DEVELOPMENT

Model-based software development provides seamless
transition from design to implementation and testing.
Based on the hardware platform described in the above
sections, control algorithms are developed using modelbased methodology to realize various fundamental
features necessary for engine operation, such as analog
input signal sampling, filtering and conversion; engine
timing detection; speed calculation and filtering; look-uptables for basic spark advance and fuel injection
duration; dwell angle calculation; ignition and injection
implementation; engine cold start strategy; Individualbank control for a dual bank engine; and UDP
communication etc.
Based on these basic control features we implement themore complex engine operation modes required by thecatalyst research and evaluation testing, throughfeedback and feed-forward mechanisms. Figure 4 shows®
part of the Simulink algorithm model of the engine
controller, which includes various algorithms for A/F ratio
control. For catalytic converter evaluation testing, OEMsmight have different procedures. The most commonly
adopted include steady state A/F ratio modulation with

Fig. 4 Part of the Engine Control Software
Steady State A/F Ratio Modulation and PhaseShifting
We design the algorithm shown in Figure 5 to realize
steady state A/F ratio modulation and phase-shifting.
The key feature of this algorithm is that the base fuelwidth which corresponds to the targeted average A/F
ratio is obtained through a feedback loop, while the highfrequency A/F ratio modulation is realized by modulating
the base fuel width with proper amplitude, frequency andphase in the feed-forward path. To obtain the base fuelwidth, the average A/F ratio during the engine operationneed be obtained. We realize this by performing a rolling
average calculation of the A/F ratio, with the time
window equal to the period of the desired A/F ratio
modulation. By doing so, we get the average A/F ratio
during the engine operation despite the A/F ratio
modulation. A PI controller is used to obtain the basefuel injection duration based on the deviation between
the targeted average A/F ratio and the real-time rolling
average value. The base fuel injection duration ismodulated with the desired frequency and amplitude, as
well as a phase shift for the phase-shifted
implementation, and output to control the engine
operation. For the case of a dual bank engine, both
Lambda sensor values upstream of the catalytic
converter are used and the banks are individuallycontrolled.

Fig. 5

Algorithm to Realize A/F Ratio Modulation andPhase-Shifting

Figure 6 shows the results of applying the above
described algorithm on a 4.6 liter V8 engine. The left andright banks are controlled individually and both lambda
values (Lambda1 and Lambda2 in Figure 1) are shown.
Figure 6(a) is the result of achieving stoichiometry as thetarget average A/F ratio, with 1 Hz modulation of 5%
perturbation amplitude, and the left and right banks inphase. Figure 6(b) shows the result of 180 degree
phase-shifted half Hz A/F ratio modulation between thebanks. We see the designed algorithm gives excellent
control performance realizing the desired A/F ratio
modulation and phase shifting.

A/F ratio is controlled to follow the square wave of 5%rich and 5% lean that lasts a certain amount of time. The
rich bias stage will remove the stored oxygen of thecatalyst. The lean stage will fill the catalyst with oxygen
until it reaches an equilibrium oxygen storage condition.
Because of the oxygen storage property, the lambda
sensor downstream of the catalyst has a delay inindicating the lean condition compared with the lambda
sensor upstream of the catalyst, until the catalyst is
saturated with oxygen. The oxygen storage capacity of
the catalyst is calculated by integrating the oxygen
entering and exiting the catalyst.
The rich-lean A/F ratio is achieved via a feed-forwardmechanism. Fuel duration look-up-tables targeting thedesired rich and lean A/F ratios are obtained andintegrated in the engine controller software to realize thisoperation mode. Figure 7 shows the result of thisapplication on the test engine. The left and right banks
are controlled individually. Figure 7(a) shows the control
performance of 120 seconds. Each of the rich and leanstages lasts 30 seconds for a 60 seconds cycle. Figure7(b) covers only 10 seconds to show the detail of a richto lean transition.

(a)
(a)

(b)
Fig. 6 Left and Right Bank Lambda Values Without andWith Phase-shifting
Rich-Lean Transition
Rich-lean transition mode is often used to measure theoxygen storage capacity of the catalyst [4,5,6]. Accurate
determination of the oxygen storage capacity will
facilitate the optimal design of A/F ratio control, allow abetter adaptive control algorithm, and also help catalyst
monitoring which is required by OBDII. In this mode, the(b)Fig. 7 Left and Right Bank Lambda Values during RichLean Transition
A/F Ratio Sweeping
Another operation mode that is used for oxygen storage
capacity measurement is A/F ratio sweeping [4]. In thismode, the engine is controlled such that the average A/F
ratio changes from rich to lean and back at a very slow
rate, lasting as much as 10 minutes for the wholesweeping cycle. During this process, a much faster (1Hz) A/F ratio modulation of certain amplitude issuperimposed on the average value. Using thismechanism, the oxygen storage capacity is determinedby calculating the perturbing oxygen quantity just before
the break-through (the downstream A/F ratio being outof stoichiometric) occurs.
The A/F ratio sweeping mode is achieved by adopting asimilar control algorithm to the steady state modulation
mode shown in Figure 5. The difference is that the target
average A/F ratio is not a constant in this mode, butfollowing the very slowly changing triangle waveform.
The high frequency A/F ratio modulation is still realizedby modulating the base fuel width in the feed-forward
path. Figure 8 shows the result of this application on thetest engine. The target average A/F ratio changes
between 5% rich and 5% lean, following the very slowly
changing triangles. The superimposed perturbation is a
1 Hz, ±2.5% modulation. An entire sweeping cycle lastsfor 10 minutes. Figure 8(a) covers about 1000 seconds
and shows very clearly the control performance offollowing the desired average A/F ratio. Figure 8(b)covers a segment of only 10 seconds to show the detailof the 1 Hz modulation during the sweeping process. It is
obvious the designed algorithm results in excellent
control performance in achieving the desired A/F ratio
modulation during the sweeping process.

(a)

(b)
Fig. 8

Left and Right Bank Lambda Values during A/F
Ratio Sweeping and Modulation

CONCLUSION
To overcome the limitations of mass production ECU, anengine rapid control prototyping system is set up in anengine dynamometer test cell environment to fulfill therequirements for catalyst research and evaluation
testing. Setting of engine operation point is performed bya real-time test cell controller. Necessary engine control
functions are realized by a rapid prototyping controller,
which adopts model-based engineering methodology forsoftware development. Algorithms to realize various A/F
ratio control features, including A/F ratio modulation ofdifferent frequencies and amplitudes, phase shift
between banks, rich-lean transition and A/F ratio
sweeping etc, are designed and implemented. UDP
communication is developed for real-time command andvariable exchange between the engine controller and thetest cell controller. The integrated system fulfills theneed of realizing various A/F ratio patterns for catalyst
research and evaluation testing. Application and resultsof the system on a 4.6L V8 gasoline engine demonstrate
the flexibility and good performance of the system.

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CONTACT
Dr. Shugang Jiang
Technical Specialist
A&D Technology Inc.
4622 Runway Blvd., Ann Arbor, MI 48108 USA
Email: sjiang@aanddtech.com