01-12-2012, 12:45 PM
DIGITAL FUEL INJECTION SYSTEM
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INTRODUCTION
All the combustion engines are design on the principle that they use some fuel as the intake and convert this into energy, to produce work. A mixture of fuel and air is a must for any combusting engine to function. Over a period Technologies have changed and evolved methods to “Feed” this mixture to the engine. The fuel injection system supplies the engine with a combustible air-fuel mixture. Old petrol Engine cars used to the conventional carburetors for supplying air-fuel mixture to the combustion Chamber. The Carburetor technology was found insufficient to cater to the needs of the challenging environment and has many this advantages like low fuel economy, High pollution rate, delayed starting, etc. Technological development in the automobile field resulted in the digital fuel injection system. The digital fuel injection system is a solution to all the problems of carburetor. The controller in a Digital Fuel Injection System is an electronic control module (ECM) or electronic control unit (ECU) the ECM controls the ignitions and fuel injection systems. Various Components of the engine and fuel system send electrical signals to the ECM and ECM continuously calculates how much to eject. It then opens the fuel injectors so the Proper amount of fuel sprays out to produce the desired air-fuel ratio.
Electronic Control Module (ECM):
The nerve centre of the Digital Fuel Injection System is the Electronic Control Module (ESM) and all the data collected from the various sensors are directed towards ECM. It serves as the processor or decision maker in an Electronic Control System. The main parts of an ECM are the IC Chips that contain the microprocessor and the memory. The microprocessor is the Central Processing Unit (CPU). It is the solid-state devise that control information flow in a computer. By following a set of instructions called program, The micro processor does the calculation and make the decisions solve. The microprocessor chip is sealed in a protective package or career. The signals from the sensors are received and sent through connections or terminals in the ECM. The information needed by the microprocessor is stored in an electronic storage device called a memory. The Random Access Memory may be volatile or non-volatile. Volatile memory stores information’s temporarily, as long as battery power is available. The information stored in a non-volatile memory is not lost by disconnecting the battery. The Look up Tables of ECM is a non-volatile type memory.
Engine speed sensor:
The engine speed sensor is actually a crank shaft position sensor that tells the ECM how fast the engine crank shaft is turning. The ECM uses this data to control fuel metering, ignition spark advance, and the shifting of electronic automatic transmissions and transaxles. Crankshaft position sensors are either Hall-effect sensors or magnetic sensors. In the case of Hall-effect switch the ECM count the number of crankshaft rotations per second. The crankshaft harmonic balance carries three vanes which pass between a permanent magnet and a transducer and the magnetic field transistor on and off, switching the signal voltage to the ECM. The ECM counts this voltage pulses to determine the crankshaft speed.
Oxygen sensor:
The oxygen sensor is installed in the exhaust manifold or exhaust pipe. It measures the amount of oxygen in the exhausted gas. It is used primarily as a means of controlling exhaust an emissions by keeping the air-fuel ratio close to 14.7:1. The oxygen sensor is about the size of as spark of plug and produces a small voltage when exposed to oxygen. This varying voltage is sent to the ECM, the voltage varies with the amount of oxygen in the exhaust. Oxygen sensor voltage is between 1.3V and 1.5V and when the voltage is close to 0.45V, the air-fuel ratio is close to ideal 14.7:1. If the voltage is higher than 0.45V, the oxygen content is low i.e. the air-fuel ratio is rich and if the voltage is less then 0.45V the oxygen content is high and the air fuel ratio is lean.
Intake temperature sensor:
Changing air temperature, changes the density of air. Hot air at low atmospheric pressure is less dense and contains less oxygen than as equal volume of cooler air under high atmospheric pressure. The intake air temperature sensor is a thermostat. Its electrical signal decreases as its temperature increases. The IAT sensor is located after the air filter and helps to compute actual density of air at the intake manifold. The IAT sensor sends varying voltage signals to the ECM and so it knows the air temperature.
Throttle position sensor (tps):
The throttle body contains the throttle valve. The assembly usually mounts on the intake manifold. The throttle valve connects by linkage to the accelerator pedal. Depressing the accelerator pedal opens the throttle valve. The ECM must always know the position of the throttle valve. A TPS on the throttle body continuously reports throttle position to the ECM. The position of throttle valve is important in the control of the idle speed and in the sharp patterns of automatic transmission and transaxles. When the throttle valve closes during the deceleration, The ECM shuts of fuel flow. This prevents and over-rich mixture during deceleration. A rotary throttle position sensor is a variable resistor or potentiometer. It has a coil of resistance in the form of a half circle. One end connects to the ground and other end connect to a 5V source from the ECM. As the throttle valve position changes, the wiper blade moves along the coil. As the wiper slides, the voltage through the coil increases and correspondingly a voltage are sent to the ECM. The voltage tells the ECM the position of the throttle valve.
ACTUATORS
Sensors feed information into the ECM. The ECM then makes decisions and sends commands to various actuators. These are the device that operates automotive and engine components Actuators are transducers that usually connect electrical signals from the ECM in to mechanical motion. Inputs are usually from sensors and switches. Outputs are usually sent to actuator, which then operates switches, valves and other devices.
ELECTRONIC PORT- INJECTION TIMING
The timing of the injection in an electronic port – injection system varies for different engines. In some four and six cylinder engines, all fuel injectors open at the same time - once each crankshaft revolution. This arrangement is the simultaneous injection system. Each injector opens twice for each time its intake valve opens. The intervals between injection and intake valve opening are short that there are short that there is little loss in efficiency. Some systems open half of the injections at the same time. This is group injection. Other systems open each injector separately in firing order sequence. This is sequential electronic fuel injection. It provides the most accurate fuel delivery and best engine performance while minimizing exhaust emissions.
CONCLUSION
1. Researchers are going on and developments are made each day in the field of fuel injection systems. The digital fuel injection system has changed the complete concept of fuel injection and resulted in better efficient and powerful vehicles.
2. Modern fuel injection systems are designed specifically for the type of fuel being used. Some systems are designed for multiple grades of fuel (using sensors to adapt the tuning for the fuel currently used)
3. Digital fuel injection system improves fuel consumption.
4. The performance of an engine suffers with the use of carburetor, but digital fuel injection system allows for the better engine performance, this is due to a few factors. Instead of allowing for additional air intake.