Abstract :
To cope up
the burning problem of high priced and vanishing fossil fuels; with research in
renewable energies, we should think for utilization of present amount of fuels
in most efficient way. This need gives rise to advancement in design,
construction and control of automotive engines. This has given rise to new
generation of more developed, light, fuel efficient “High Tech” vehicles.
Recent innovations in engine design and control have been adopted very widely
and rapidly.
In this
paper, we are concentrating on Control Systems in automobiles as these have
direct contribution in fuel economy. For the engine to run, it must have good
compression ratio, properly timed spark ignition, proportionate air-fuel
mixture and enough hot sparks to ignite the mixture. If any of these conditions
is missing, the engine won’t start or run properly and finally it affects fuel
economy. Air-fuel Injection, Ignition, Exhaust Systems are the main components
of control system.
The
principle of Electronic Fuel Injection System is, the different sensors like
TPS, CPS senses the changes in engine assembly and send electric signal to Electronic
Control Module (ECM) which continuously calculates how much fuel is to be
injected to achieve stoichiometric combustion.
In the Ignition System, Knock,
Throttle Position Sensors feed corresponding information to computer which
decides correct timing of spark. This system of spark ignition can develop
47,000 V or more and produces longer and
correct timed spark which ignites leaner air fuel ratios for better fuel
economy and reduces exhaust emission. In Exhaust System, oxidizing and 3-way
catalysts reduce harmful combustion products like NOx , CO
Advantages
of computer controlled engines are improvement in fuel economy, improved
reliability, system failure diagnosis, warning of engine malfunctioning. Most
of recent vehicles are now equipped with electronic ignition systems. A few of
these include electronic engine control and management to which we are now
familiar as VTi, DTSi, DICOR, AMI engines; sequential port injection, multiport
fuel injection and throttle body fuel injection. Suitable combinations of
advanced control systems and alternate fuels in vehicles will surely solve the
most critical problem of fossil fuel up to some extent.
ELECTRONIC
CONTROL MODULE (ECM):-
“This is
unit of automobile computer system which can receive signals, process them,
make decisions and send commands that control other devices”.
Following sensors
monitor the engine, transmission, air-intake, exhaust, vehicle speed, fuel
flow, and many other things that affect engine performance. The ECM uses this
information to control fuel supply, the timing of fuel injections, and the mix
of fuel and air in the engine’s combustion chambers. Modern ECMs also control
the engine’s ignition system, which ignites fuel in the combustion chambers at
precisely timed intervals to operate the engine efficiently. Such systems may
be controlled by single engine computer or by separate computers.
BLOCK
DIAGRAM OF ELECTRONIC CONTROL SYSTEM.
ELECTRONIC
FUEL INJECTION SYSTEM:-
In trying
to keep up with emission laws and fuel efficiency, the fuel system used in
modern cars has changed a lot, over the years. The fuel-injection system
replaces the carburetor in most new vehicles to provide more efficient fuel
delivery system. The components of an electronic fuel-injection system include
injectors, a pump that delivers fuel from a storage tank to the injector, a variety
of sensors throughout the vehicle and ECM.
There are
two types of Injection system used in SI engines are
1) Multiport
Fuel Injection (MFI): It has fuel
injector in each intake port.
2) Throttle
Body Fuel Injection (TBI): It has one or two fuel injectors located above the
throttle valve.
Principle:-“Electronic
sensors respond to varying engine speeds and driving conditions by changing the
ratio of fuel to air. The sensors send a fine mist of fuel from the fuel supply
through a fuel-injection nozzle into a combustion chamber, where it is mixed
with air. The mixture of fuel and air triggers ignition”.
Working: - ECM
continuously receives information about engine speed, throttle position, intake
air amount, pressure and temperature, amount of oxygen from sensors. ECM checks
this data with other data stored in lookup tables in its memory. Then ECM
decides when to open the fuel injectors and for how long. The length of pulse
opens injection valve for the proper duration of time. In order to provide the
correct amount of fuel for every operating condition, the engine control unit
(ECU) has to monitor large number of input sensors. Here are some of them:-
Mass
Airflow Sensor – It measures flow rate of air by speed density or air flow
metering and provides electrical output to ECM that is proportional to flow
rate of air entering the engine.
Oxygen
sensor – It is installed in exhaust manifold and measures amount of oxygen in
exhaust gas. It works by comparing the oxygen content of exhaust gas to that of
outside air and produces small voltage varying with amount of oxygen and sends
to ECM. So the ECM can determine how rich or lean the fuel mixture is and make
adjustments accordingly.
Throttle
Position Sensor – It is mounted on throttle body monitors the throttle valve
position which determines how much air entering into the engine so the ECU can
respond quickly to changes, increasing or decreasing the fuel rate as necessary
Coolant
Temperature Sensor – It is a thermistor. It continuously reports ECM about
engine coolant temperature. It allows the ECU to determine when the engine has
reached its proper operating temperature.
Manifold
Absolute Pressure Sensor – It monitors the pressure of the air in the intake
manifold. The amount of air being drawn into the engine is a good indication of
how much power it is producing and the more air that goes into the engine,
lower the manifold pressure, so this reading is used by ECM to gauge how much
power is being produced.
Engine
Speed Sensor – It reports about speed of crankshaft. ECM uses this data to
control fuel metering, ignition spark advance and the shifting of electronic
automatic transmission.
Calculation
of Pulse Width: The engine control unit uses a formula and a large number of
lookup tables to determine the pulse width for given operating conditions. The
equation will be a series of many factors multiplied by each other. Many of
these factors will come from lookup tables. e.g. following equation will only
have three factors, whereas a real control system might have a hundred or more.
Pulse width
= (Base pulse width) x (Factor A) x (Factor B) In order to
calculate the pulse width, the ECU first looks up the base pulse width in a
lookup table. Base pulse width is a function of engine speed (RPM) and load
(which can be calculated from manifold absolute pressure). A and B are
parameters that come from sensors. e.g. A is coolant temperature and B is oxygen
level.
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