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Engine management system

What is an engine management system?

Engine Management System or EMS is a self contained custom built computer which controls

The running of an engine by monitoring the engine speed, load and temperature.

Providing the ignition spark at the right time for the prevailing conditions .

Metering the fuel to the engine in the exact quantity required.

The engine management system ensures that the driver request is implemented; for example, it converts the acceleration/deceleration requests into a corresponding engine output.

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Fuel tank. Holds a reservoir of fuel for the engine.Fuel filter. "pre-filter" prevents rubbish from entering the pump.Fuel pump.A high-pressure pump running at around 6 bar which supplies fuel to the injectors. The fuel pressure regulator regulates to this pressure between 3 and 4 bar.

Fuel line.Fuel pipe that transports the fuel from the pump to the fuel rail.Fuel rail.A small fuel gallery from which the injectors take their fuel supply.Fuel Injectors. Electric valves which when open allow fuel to be injected into the engine under high pressure.Pressure regulator.A device that keeps the fuel pressure at a constant rate and returns any excess fuel to the tankFuel return line. Fuel pipe which bleeds excess fuel back to the fuel tank

The engine management system

It is necessary to provide

needed accuracy and adaptability in order to minimise exhaust emissions and fuel consumption.

optimal driveability for all operating condition.

minimise evaporative emission (gasoline engines) and

system diagnosis when malfunctions occur.

Exhaust Emissions

The engine exhaust consists of products from the combustion of the air and fuel mixture.

Under perfect combustion conditions the hydrocarbons would combine in a thermal reaction with oxygen in the air to form carbon dioxide (CO2) and water (H2O).

Unfortunately perfect combustion does not occur and in addition to CO2 and water, carbon monoxide (CO), oxides of nitrogen (NOX) and hydrocarbon (HC) occur in the exhaust as a result of combustion reaction.

Additives and impurities in the fuel also generate minute quantities of pollutants such as lead oxides, lead halogenides and sulphur oxides.

Fuel consumption

A lot of different factors are working in partnership to make of central importance fuel economy:

The need of a better and more rational use of energetic resources to reach a sustainable growth

The fuel price increase and its market consequence

The electronic engine control system provides the fuel metering and ignition timing precision required to minimise fuel consumption.

Driveability

Another requirement of the electronic engine control system is to provide acceptable driveability under all operating conditions.

No stalls, hesitations or other objectionable roughness should occur under vehicle operation.

Driveability is influenced by almost every operation of the control system and, unlike exhaust emissions or fuel economy, is not easily measured.

Other factors that influence driveability are the idle speed control, exhaust gas recirculation(EGR) control and evaporative emissions control.

Idle speed

Idle speedis the rotational speed the engine runs on when the engine is uncoupled to the drivetrain and the throttle pedal isn't depressed (generally measured in revolutions per minute, or rpm).

At idle speed, the engine generates enough powerto run reasonably smoothly and operate its ancillaries (water pump, alternator and, if equipped, other accessories such as power steering).

But usually not enough to perform useful work, such as moving an automobile.

The idle speed control (ISC) system regulates engine idle speed by adjusting the volume of air that is allowed to by-pass the closed throttle valve.

The ECU controls the idle speed control valve (ISCV) based on input signals received from various sensors.

Evaporative Emissions (Gasoline engine only)

Hydrocarbon (HC) emissions in the form of fuel vapours escaping from the vehicle are closely regulated.

The prime source of these emissions is the fuel tank. Due to ambient heating of the fuel and the return of unused hot fuel from the engine, fuel vapours are generated in the tank.

The evaporative emission control system (EECS) is used to control the evaporative HC emissions. The fuel vapours are rotated to the intake manifold via the EECS and they are burned in the combustion process.

The quantity of fuel vapours delivered to the intake manifold must be metered such that exhaust emissions and driveability are not adversely effected. The metering is provide by a purge control whose function is controlled by the electronic control unit.

System Diagnostics

The purpose of system diagnostics is to provide a warning to the driver when the control system determines a malfunction of a component or a system and to assist the service technician in identify and correct the failure.

To the driver the engine may appear to be operating correctly, but excessive amounts of pollutants may be emitted. The ECU determines a malfunction has occurred when a sensor signal, received during normal engine operation or during a system test, indicates there is a problem.

System Diagnostics

For critical operations such as fuel metering and ignition control, if a required sensor input is faulty, a substitute value may be used by the ECU so that the engine will continue to operate.

Starting from 2001 (Euro3) the European On Board Diagnosis (EOBD) statutes require that, when a failure occur in a system critical for exhaust emissions, the malfunctioning indicator lamp (MIL), visible to the driver, must be illumined. Information on the failure is stored in the ECU. A service technician can retrieve the information on the failure on the ECU and correct the problem.

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ECU

SENSORS

ACTUATORS

The engine control system includes:

sensors for the detection of the engine operating modes

electronic control unit (ECU) which elaborates the signal values supplied by the sensor, according to defined control strategies and algorithms, and defines the actions to be delivered to the actuators

actuators which have the task to actuate the defined commands

System layout

The key sensors

Load sensor (Mass Flowmeters) Mass flowmeters operate according to the hot-wire or hot-film principle without any moving mechanical part inside the unit.

The closed-loop control circuit in the meters housing maintains a constant temperature differential between a fine platinum wire or thin-film resistor and the passing air stream.

The current required for heating provides an extremely precise, albeit nonlinear, index of air-mass flow rate; the ECU converts the signal into linear form.

Due to its closed-loop design, this air-mass meter can monitor flow variations in the millisecond range.

Oxygen sensor The fuel metering system of spark ignition engine employs the exhaust-gas residual-oxygen content as measured by the lambda oxygen sensor to regulate very precisely the air/fuel mixture for combustion to the value lambda = 1 (stoichiometric combustion).

The lambda calculation determines the ratio between the amount of oxygen actually present in a combustion chamber vs. the amount that should have been present to obtain perfect combustion.

When a mixture contains exactly the amount of oxygen required to burn the amount of fuel present, the ratio will be one to one (Ll) and lambda will equal 1.00. If the mixture contains too much oxygen for the amount of fuel (a lean mixture), lambda will be greater than 1.00. If a mixture contains too little oxygen for the amount of fuel (a rich mixture), lambda will be less than 1.00.

The oxygen sensor is a solid electrolyte made of ZrO Zirconium Oxide ceramic material that becomes electrically conductive for oxygen ions at temperature higher than 300C.

A galvanic charge is generated at the sensor terminals, which are design as porous platinum thick-film electrodes and coated with a ceramic spinel layer: the voltage varies to the greatest extend at the lambda value of 1.

Engine speed sensor Generally a Magnetic Speed Sensor detects when ring gear teeth, or other ferrous projections, pass the tip of the sensor. Electrical impulses are produced by the sensors internal coil and sent to the speed control unit. The signal from the magnetic speed sensor, teeth per second (Hz.), is directly proportional to engine speed.

Assignment

Explain briefly Electronic control of braking and traction.

Explain Navigation systems in Automotives.

Write notes on

i) Electronic transmission control.

Ii)Vehicle safety system.

DOS: