Electronic

Engine Control
INTRODUCTION
⚫ Engine control means regulating fuel and
air intake as well as spark timing to
achieve desired performance in the form
of torque or power output.

⚫ Until the late 1960s, control of the engine

output
torque and RPM was accomplished
through some combination of mechanical,
pneumatic, or hydraulic systems.

⚫ Then, in the 1970s, electronic control

systems were introduced.
MOTIVATION FOR
ELECTRONIC ENGINE
CONTROL

⚫Electronic engine control came in

part due to two government
requirements.
⚫legislation to regulate automobile
exhaust emissions under the
authority of the Environmental
Protection Agency (EPA).
⚫To improve the national average
Exhaust Emissions

⚫The engine exhaust consists of the

products of combustion of the air
and gasoline mixture.
⚫Gasoline is a mixture of chemical
compounds that are called
hydrocarbons.
⚫Gasoline also contains natural
impurities as well as chemicals added
by the refiner.
⚫All of these can produce undesirable
⚫During the combustion process, the
carbon and hydrogen combine with
oxygen from the air, releasing heat
energy and forming various
chemical compounds.

⚫If the combustion were perfect, the

exhaust gases would consist only of
carbon dioxide (CO2) and water
(H2O), neither of which are
considered harmful in the
atmosphere.
⚫Unfortunately, the combustion of
the SI engine is not perfect. In
addition to the CO2 and H2O, the
exhaust contains amounts of carbon
monoxide (CO), oxides of nitrogen
(chemical unions of nitrogen and
oxygen that are denoted NOx),
unburned hydrocarbons (HC), oxides
of sulfur, and other compounds.
⚫Some of the exhaust constituents are
considered harmful and have come
under the control of the federal
government. The exhaust emissions
⚫Automotive exhaust emission
control requirements started in the
United States in 1966
⚫The federal government has
imposed emission control limits for
all states, and the standards became
progressively more difficult to meet
through the decade 1970–1980.
⚫Auto manufacturers found that the
traditional engine controls could not
control the engine sufficiently to
meet these emission limits and
Fuel Economy
⚫ Fuel economy is related to the number of
miles that can be driven for each gallon of
gasoline consumed. It is referred to as miles
per gallon (MPG) or simply mileage.
⚫ Another important feature of electronic
engine control is its ability to improve fuel
economy.
⚫ Electronic engine control is used to reduce
exhaust emissions and improve fuel
economy, both of which have limits set by
the government.
⚫ The mileage of a vehicle is not unique. It
depends on size, shape, weight, and how the
car is driven. The best mileage is achieved
under steady cruise conditions.
CONCEPT OF AN ELECTRONIC ENGINE
CONTROL SYSTEM

⚫In order to understand electronic

engine control it is necessary to
understand some fundamentals of
how the power produced by the
engine is controlled.
⚫The throttle directly regulates the
power produced by the engine at any
operating condition. It does this by
controlling the air flow into the
engine.
⚫ The mass flow rate of air into the engine
varies directly with throttle plate angular
position .
⚫ As the driver depresses the accelerator
pedal, the throttle angle ( θ in Figure 5.3)
increases, thereby allowing an increased
air flow into the engine.
⚫ The role of fuel control is to regulate the
fuel that is mixed with the air so that it
increases in proportion to the air flow.
⚫ The performance of the engine is affected
strongly by the mixture (i.e., by the ratio
of air to fuel). However, for any given
mixture the power produced by the
⚫Engine power is given in
kilowatts (kw) and air mass is
given in kilograms (kg). In
mathematical terms we can
write:
⚫Pb = KMA
⚫where
⚫Pb = power from the engine (hp or
kw)
⚫MA = mass air flow rate (kg/hr)
⚫K = constant relating power to air
⚫An electronic engine control
system is an assembly of
electronic and electromechanical
components that continuously
varies the fuel and spark settings
in order to satisfy government
exhaust emission and fuel
economy regulations.
⚫ Figure shows a block diagram of
a generalized electronic engine
control system.
⚫control system requires
measurements of certain
variables that tell the controller
the state of the system being
controlled.
⚫The electronic engine control
system receives input electrical
signals from the various sensors
that measure the state of the
engine. From these signals, the
controller generates output
Engine Functions and Control
⚫ Figure identifies the automotive functions
that surround the engine.
⚫ There is a fuel metering system to set the
air–fuel mixture flowing into the engine
through the intake manifold.
⚫ Spark control determines when the air–
fuel mixture is ignited after it is
compressed in the cylinders of the engine.
⚫ The power is delivered at the driveshaft,
and the gases that result from combustion
flow out of the exhaust system.
⚫ In the exhaust system, there is a valve to
control the amount of exhaust gas being
recirculated back to the input, and a
DEFINITION OF GENERAL TERMS
Parameters
⚫ A parameter is a numerical value of some engine dimension
that is fixed by design.
Examples
⚫ piston diameter (bore),
⚫ distance the piston travels on one stroke (stroke),
⚫ length of the crankshaft lever arm (throw).
⚫ The bore and stroke determine the cylinder volume and
the displacement.
⚫ Displacement is the total volume of air that is displaced as
the engine rotates through two complete revolutions.
⚫ Compression ratio is the ratio of cylinder volume at BDC to
the volume at TDC.
⚫ Other parameters that engine designers must specify
include combustion chamber shape, camshaft cam
profile, intake and exhaust valve size, and valve
timing.
⚫ All of these design parameters are fixed and are not
subject to control while the engine is operating.
 Variables
⚫ A variable is a quantity that changes or may be
changed as the engine operates, typically under the
control of the electronic control system.
Examples
mass air flow, fuel flow rate, spark timing,
power, intake manifold pressure, and.
Inputs to Controllers.
Figure identifies the major physical quantities that
are sensed and provided to the electronic
controller as input
1. Throttle position sensor (TPS)
2. Mass air flow rate (MAF)
3. Engine temperature (coolant temperature) (CT)
4. Engine speed (RPM) and position
Outputs from Controllers
Figure identifies the major physical
quantities that are outputs from the
controller. These outputs are
1. Fuel metering control
2. Ignition control
3. Ignition timing
4. Exhaust gas recirculation control
 ENGINE PERFORMANCE TERMS

Power
⚫ The most common performance rating that
has been applied to automobiles is a power
rating of the engine. It normally is given in
kilowatts .
⚫ Power is the rate at which the engine is doing
useful work. It varies with engine speed and
throttle angle.
⚫ Power may be measured at the drive wheels
or at the engine output shaft.
⚫ The power delivered by the engine to the
dynamometer is called the brake power and
is designated Pb.
⚫ The brake power of an engine is always less
than the total amount of power that is
actually developed in the engine.
⚫ This developed power is called the
indicated power of the engine and is denoted
Pi.
⚫ The indicated power differs from the
brake power by the loss of power in the
engine due to friction between cylinders
and pistons, and other friction losses.
BSFC
⚫ Fuel economy can be measured while the engine
delivers power to the dynamometer. The engine
is typically operated at a fixed RPM and a fixed
brake power (fixed dynamometer load), and the
fuel flow rate (in kg/hr) is measured.
⚫ The fuel consumption is then given as the ratio of
the fuel flow rate (rf) to the brake power output
(Pb). This fuel consumption is known as the
brake-specific fuel consumption , or BSFC.

⚫ By improving the BSFC of the engine, the fuel

economy of the vehicle in which it is installed is
also improved. Electronic controls help to
Torque
⚫ Engine torque is the twisting action produced
on the crankshaft by the cylinder pressure
pushing on the piston during the power
stroke.
⚫ Torque is produced whenever a force is
applied to a lever. The length of the lever in
the engine is determined by the throw of the
crankshaft
⚫ The torque is expressed as the product of this
force and the length of the lever.
⚫ The units of torque are N⋅m (Newton meters)
in the metric system or ft lb (foot-pounds) in
the U.S. system.
⚫ The torque of a typical engine varies with
Volumetric Efficiency
⚫ The variation in torque with RPM is
strongly influenced by the volumetric
efficiency, or “breathing efficiency.”
⚫ Volumetric efficiency actually describes how
well the engine functions as an air pump,
drawing air and fuel into the various
cylinders.
⚫ It depends on various engine design
parameters such as piston size, piston
stroke, and number of cylinders.
Thermal efficiency
⚫ Thermal efficiency expresses the mechanical energy
that is delivered to the vehicle relative to the
energy content of the fuel.
⚫ In the typical SI engine, 35% of the energy
that is available in the fuel is lost as heat to
the coolant and lubricating oil, 40% is lost as
heat and unburned fuel in exhaust gases, and
another 5% is lost in engine and drivetrain
friction.
⚫ This means that only about 20% is available to
drive the vehicle and accessories. These
percentages vary somewhat with operating
conditions but are valid on the average.
Calibration

⚫The definition of engine

calibration is the setting of the
air/fuel ratio and ignition timing
for the engine.
⚫With the new electronic control
systems, calibration is
determined by the electronic
engine control system.
ENGINE MAPPING
⚫ The development of any control system comes
from knowledge of the plant, or system to be
controlled. In the case of the automobile engine,
this knowledge of the plant (the engine) comes
primarily from a process called engine mapping.
⚫ For engine mapping, the engine is connected to a
dynamometer and operate throughout its entire
speed and load range. Measurements are made of
the important engine variables while quantities,
such as the air/fuel ratio and the spark control,
are varied in a known and systematic manner.
⚫ Such engine mapping is done in engine test cells
that have engine dynamometers and complex
instrumentation that collects data under
computer control.
⚫ From this mapping, a mathematical model is
developed that explains the influence of every
measurable variable and parameter on engine
performance.
⚫ The control system designer must select a control
Effect of Air/Fuel Ratio on
Performance
⚫Note from Figure that torque (T)
reaches a maximum in the air/fuel
ratio range of 12 to 14.
⚫The CO and unburned
hydrocarbons tend to decrease
sharply with increasing air/fuel
ratios.
⚫Unfortunately for the purposes of
controlling exhaust emissions, the
Nox exhaust concentration increases
with increasing air/fuel ratios.
⚫ The air/fuel ratio has a significant effect on engine
torque and emissions.
⚫ Figure illustrates the variation in the performance
variables of torque (T) and brake power (BSFC) as well
as engine emissions with variations in the air/fuel
ratio with fixed spark timing and a constant engine
speed.
⚫ In this figure the exhaust gases are represented in
brake-specific form. This is a standard way to
characterize exhaust gases whose absolute emission
levels are proportional to power.
⚫ The definitions for the brake-specific emission rates
are
⚫ One specific air/fuel ratio is highly significant in
electronic fuel control systems, namely, the
stoichiometric mixture.
⚫ The stoichiometric (i.e., chemically correct) mixture
corresponds to an air and fuel combination such
that if combustion were perfect all of the
hydrogen and carbon in the fuel would be
converted by the burning process to H2O and
CO2.
⚫ Stoichiometry is sufficiently important that
the fuel and air mixture is often represented
by a ratio called the equivalence ratio, which is
given the specific designation λ.
⚫ The equivalence ratio is defined as follows:

⚫ A relatively low air/fuel ratio, below 14.7

(corresponding to λ < 1), is called a rich mixture
⚫ an air/fuel ratio above 14.7 (corresponding to λ >
1) is called a lean mixture.
⚫ Emission control is strongly affected by air/fuel
ratio, or by λ.
Effect of Spark Timing on Performance
⚫ Spark advance is the time before top dead
center (TDC) when the spark is initiated.
⚫ Figure 5.9 reveals the influence of spark
timing on brakespecific exhaust emissions
with constant speed and constant air/fuel
ratio.
⚫ Note that both NOx and HC generally
increase with increased advance of spark
timing. BSFC and torque are also strongly
influenced by timing. Figure 5.9
⚫ shows that maximum torque occurs at a
particular advanced timing referred to as
minimum advance for best timing (MBT).
⚫ Operation at or near MBT is desirable since
this spark timing tends to optimize
Effect of Exhaust Gas Recirculation on
Performance
⚫ By adding another calibration parameter, the
undesirable exhaust gas emission of NOx can be
significantly reduced while maintaining a relatively
high level of torque.
⚫ This new parameter, exhaust gas recirculation (EGR),
consists of recirculating a precisely controlled amount of
exhaust gas into the intake.
⚫ Exhaust gas recirculation is a major subsystem of the
overall control system. Its influence on emissions is
shown in Figures 5.10 and 5.11 as a function of the
percentage of exhaust gas in the intake.
⚫ Figure 5.10 shows the dramatic reduction in NOx
emission when plotted against air/fuel ratio
⚫ Figure 5.11 shows the effect on performance variables
as the percentage of EGR is increased.
⚫ Note that the emission rate of NOx is most strongly
influenced by EGR and decreases as the percentage of
EGR increases. The HC emission rate increases with
⚫The mechanism by which EGR affects
NOx production is related to the peak
combustion temperature.
⚫Roughly speaking, the NOx generation
rate increases with increasing peak
combustion temperature if all other
variables remain fixed.
⚫Increasing EGR tends to lower this
temperature therefore, it tends to
lower NOx generation.
catalytic converter
⚫ The catalytic converter reduces the concentration of
undesirable exhaust gases coming out of the tailpipe
relative to engine-out gases (the gases coming out of the
exhaust manifold).
⚫ The use of catalytic converters to reduce emissions leaving
the tailpipe allows engines to be calibrated for better
performance and still meet emission regulations.
⚫ catalytic converter reduces exhaust gas emission
concentrations by 90%, the engine exhaust gas emissions at
the exhaust manifold can be about 10 times higher than the
requirements. This has the significant benefit of allowing
engine calibration to be set for better performance than
would be permitted if exhaust
emissions in the engine exhaust manifold had to satisfy
EPA regulations.
⚫ This is the type of system that is chosen for the typical
electronic engine control system. Several types of catalytic
converters are available for use on an automobile.
⚫ The desired functions of a catalytic converter include
1. Oxidation of hydrocarbon emissions to carbon dioxide
(CO2) and water (H2O)
2. Oxidation of CO to CO2
ELECTRONIC FUEL CONTROL SYSTEM

⚫ The primary function of fuel control system is to

accurately determine the mass air flow rate into the
engine.
⚫ Then the control system precisely regulates fuel
delivery such that the ratio of the mass of air to the
mass of fuel in each cylinder is as close as possible to
stoichiometry (i.e., 14.7).
⚫ The components of this block diagram are as follows:
1. Throttle position sensor (TPS)
2. Mass air flow sensor (MAF)
3. Fuel injectors (FI)
4. Ignition systems (IGN)
5. Exhaust gas oxygen sensor (EGO)
6. Engine coolant sensor (ECS)
7. Engine position sensor (EPS)
⚫ The EPS has the capability of measuring crankshaft
angular speed (RPM) as well as crankshaft angular
position when it is used in conjunction with a stable
and precise electronic clock (in the controller).
⚫ The EPS has the capability of measuring
crankshaft angular speed (RPM) as well as
crankshaft angular position when it is used in
conjunction with a stable and precise
electronic clock (in the controller).
⚫ The signals from the various sensors enable
the controller to determine the correct fuel
flow in relation to the air flow to obtain the
stoichiometric mixture.
⚫ From this calculation the correct fuel delivery
is regulated via fuel injectors.
⚫ In addition, optimum ignition timing is
determined and appropriate timing pulses
are sent to the ignition control module (IGN).