Petrol vehicles uses device called carburetor for supplying the air fuel mixture in correct ratio to cylinders in all rpm ranges. due to construction of the carburetor is relatively simple, it has been used almost exclusively on gasoline engines in the past. However in response to recent demands for cleaner exhaust emission, more economical fuel consumption, improved drivability, etc., the carburetor now must be equipped with various compensating devices, making it more complex system.
So In place of the carburetor, therefore, the MPFI (multi point fuel injection) system is used, assuring proper air fuel ratio to the engine by electrically injecting fuel in accordance with various driving conditions.
MPFI system injects fuel into individual cylinders, based on commands from the Ëœon board engine management system computerâ„¢ â€œ popularly known as the Engine Control Unit/ECU. These techniques result not only in better Ëœpower balanceâ„¢ amongst the cylinders but also in higher output from each one of them, along with faster throttle response. The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions.
2. MAIN COMPONENTS OF MPFI SYSTEM
This system has four major components they are:
a) Air intake system
b) Fuel delivery system
c) Electronic control system
2.1. Air intake system
. The air (corresponding to the throttle valve opening) is filtered by the air cleaner, passes through the throttle body, and is distributed by the intake manifold and finally drawn into each combustion chamber. When the lAC valve is opened according to the signal from ECM, the air bypasses the1hrottle valve through bypass passage and is finally drawn into the intake manifold Ã‚Â¬
a. Throttle body
. The throttle body consists of the main bore, air bypass passage and the following parts. Throttle valve, which is interlocked with the accelerator pedal and controls the amount of the intake air. TP sensor which detects the throttle valve opening and sends a signal to ECM. lAC valve, which supplies the bypass, air depending on Engine condition.
b. Idle air control valve
The lAC valve controls opening of the bypass air passage. The air bypasses the throttle valve through bypass passage and is finally drawn into the intake manifold. Opening and closing of the valve itself is determined by
operation of the magnet, which is connected to it. The magnet operates according to electric current from ECM.
2.2. Fuel delivery system
The fuel in the fuel tank is pumped up by the fuel pump, filtered by fuel filter and fed under pressure to each injector through the delivery 'pipe. As the fuel pressure applied to the injector is always kept a certain amount higher than the pressure in the intake manifold by the fuel pressure regulator, the fuel is injected into the intake port of the cylinder head when the injector opens according to the injection signal form ECM. The fuel relieved by the fuel pressure regulator return through the fuel return to the fuel tank.
a. Fuel pump
The electrical fuel pump located on the fuel tank consists of armature, magnet, impeller, brush, check valve etc.The ECM controls its operation. When the power is supplied to the fuel pump, the motor in the pump runs and so does the impeller. This causes a pressure difference to occur between both sides of the impeller, as there are many grooves around it. Then the fuel is drawn through the inlet port, and with its pressure increases,
It is discharged through the outlet port, The fuel pump also has a check valve to keep some pressure in the fuel feed line even when the fuel pump is stopped.
b. Pressure regulator system
The fuel pressure regulator is diaphragm operated relief valve consisting of diaphragm, spring and valve. It keeps the fuel pressure applied to the injector 2.9Kglcm^2 higher than intake manifold at all times, The pressure applied to the upper chamber of the fuel pressure regulator intake manifold pressure and that to the lower chamber is fuel pressure. When the fuel pressure rises more than 2,9Kg/cm2 higher than the intake manifold pressure, the fuel pushes the valve in the regulator open and excess fuel return to the fuel tank through return line.
Each cylinder has one injector. Which is installed between the intake manifold delivery pipe. It is an electromagnetic type injection nozzle, which injects fuel into the intake port of the cylinder head according to the signal from ECM. When the solenoid coil of the injector is energised by ECM, it becomes an Electro magnet and attracts the plunger. At the same time, the ball valve which is incorporated with the plunger opens and the injector which is under the fuel pressure injects fuel. As the lift stroke of the ball valve of the injector is set constant, the amount of fuel injected at one time is determined by the length of the time during which the solenoid is energized
2.3. Electronic control system
The electronic control system consist of various sensors which detect the state of engine and driving conditions, ECM which controls various devices according to the signals from the sensors and Various controlled devices. The systems are
Fuel injection control system
Idle speed control system
Fuel pump control system,
Ignition control system,
Radiator fan control system,
Fuel injection control system
The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions. It uses the sequential multi-port fuel injection system, which injects fuel into each intake port of the cylinder head. In this system ECM controls the time and timing of the fuel injection from the fuel injector into the cylinder head intake port according to the signals from the various sensors so that suitable air/fuel mixture is supplied to the engine in each driving condition. The factors to determine the injection time are the basic injection time which is calculated on the basis of the engine speed and the intake manifold pressure and various compensation which are determined according to the signals from various sensors that detect the state of the engine and driving conditions.
Idle speed control system
This system controls the bypass airflow by means of ECM & lAC valve for the following purposes. To keep the engine idle speed as specified at all times. The engine idle speed can vary due to load applied to engine, to improve starting performance of the engine to compensate air fuel mixture ratio when -decelerating, to improve drivability while engine is warmed up. lAC valve operates according to duty signal sent from ECM. ECM detects the engine condition by using the signals from various signals and switches and controls the bypass airflow by changing lAC valve opening. When the vehicle is at a stop, the throttle valve is at the idle position and the engine is running, the engine speed is kept at a specified idle speed.
Fuel pump control system
ECM controls ON/OFF operation of the fuel pump by turning it ON, the fuel pump relay under any of the conditions. For two seconds after ignition switch ON. While cranking engine (while engine start signal is inputted to ECM). While crankshaft position sensor or camshaft - position sensor signal is inputted to ECM.
Ignition control system
This system controls electronically the time of electric current flow to ignition primary coil as well as ignition timing. ECM judges the engine and vehicle conditions by using signals from various sensors, selects the
most suitable electric current flow time and ignition timing for that engine and vehicle conditions from among those Prestored in its memory and sends an ignition signal to the igniter in ignition coil assembly. Controls of this system include three different types as follows. Ignition timing control at engine start, ignition timing control after engine start, electric current flow time control.
Radiator fan control system
This system controls operation (ON/OFF) of the radiator fan motor. Radiator fan motor is turned ON and OFF by its relay when ECM controls. Radiator fan motor turned ON at below 98Ã‚Â°C and OFF at below 93Ã‚Â°C
a. Engine Control Module (ECM)
ECM is installed to the underside of the instrument panel at the passenger's seat side. ECM is a precision unit consisting of microcomputer, analogue/digital converter input/output unit etc. It is an essential part of the electronic control system for its functions include not only such a major function as to control fuel injector, lAC valve, fuel pump relay, etc. But, also on-board diagnostic system (self-diagnosis function) and fail-safe function.
WORKING OF MPFI.
b. On-Board diagnostic system
ECM diagnosis troubles which may occur in the area including the following parts when the ignition switch is ON and the engine is running, and indicates the result by turning on or flashing malfunction indicator lamp (CHECK ENGINE LIGHT)
1. Oxygen sensor 2. Engine coolant temp sensor.3.TP sensor 4. IATsensor.5.MAP sensor
6.CMP sensor. 7. VS sensor. 8. CKP sensor. (MY 416).9 CPU of ECM. ECM and malfunction indicator lamp (MIL) operate as follows Malfunction indicator lamp lights when the ignition switch is turned ON but engine at stop with the diagnosis switch terminal ungrounded regardless of the condition of electronic fuel injection system. This is only to check the malfunction indicator lamp bulb and its circuit.If the above
areas of electronic fuel injection system; is free from any trouble after the engine start while engine is running. Malfunction indicator lamp turns OFF. When ECM detects a trouble which has occurred in the above areas, it makes malfunction indicator lamp turn ON while the engine is running to warn the driver of such occurrence of trouble and at the same time is stores the trouble area in ECM back-up memory. The memory is kept as it is even if the trouble was only temporary and disappeared immediately. And it is not erased unless the power to ECM is shut off for specified time 60 sec. or longer. ECM also indicates trouble area in memory by means of flashing of malfunction indicator lamp at the time of inspection.
. Fail- safe function
Even when a trouble has occurred in such area of electronic fuel injection system that includes the following parts and a failure signal is sent to ECM. control over the injector, idle air control valve and others is maintained on the basis of the standard signals and/or CPU. This function is called failsafe function. Thus with this function a certain level of engine performance is available even when some failure occurs in such area and disability in running is avoided.
3. EMISSION CONTROL SYSTEM
The need to control the emissions from automobiles gave rise to the computerization of the automobile. Hydrocarbons, carbon monoxide and oxides of nitrogen are created during the combustion process and are emitted into the atmosphere from the tail pipe. There are also hydrocarbons emitted as a result of vaporization of gasoline and from the crankcase of
the automobile. Manufacturersâ„¢ are adding of pollution control devices and the creation of a self adjusting engine. 1981 saw the first of these self adjusting engines. They were called feedback fuel control systems.
Emission control in Petrol engine passenger cars
A petrol engine without emission control produces large emissions of nitrogen oxides and unburnt hydrocarbons. The technology that manufacturers have used to meet stiffer emission requirements is the three-
way catalytic converter and new technology such as MPFI, it maintain proper air fuel mixture at stoichiometric ratio by the use of sensors in the engine, there by ensuring proper combustion of the air fuel mixture due to this it reduces the emissions from the vehicles.
3.1 Catalytic converter
Automotive emissions are controlled in three ways, one is to promote more complete combustion so that there are less by products. The second is to reintroduce excessive hydrocarbons back into the engine for combustion and the third is to provide an additional area for oxidation or combustion to occur. This additional area is called a catalytic converter. The catalytic converter looks like a muffler. It is located in the exhaust system ahead of the muffler. Inside the converter are pellets or a honeycomb made of platinum or palladium. The platinum or palladium are used as a catalyst ( a catalyst is a substance used to speed up a chemical process). As hydrocarbons or carbon monoxide in the exhaust are passed over the catalyst, it is chemically oxidized or converted to carbon dioxide and water. As the converter works to clean the exhaust, it develops heat. The dirtier the exhaust, the harder the converter works and the more heat that is developed. In some cases the converter can be seen to glow from excessive heat. If the converter works this hard to clean a dirty exhaust it will destroy itself. Also leaded fuel will put a coating on the platinum or palladium and render the converter ineffective.
Catalytic oxidizers are used in most cars around the world. Because catalytic oxidizers cannot operate in the presence of lead, their introduction caused leaded gasoline to be phased out. Ideally the byproducts of an automobile engine are only carbon dioxide, water, and some nitrogen. This is similar to the chemical output of animals. But in practice, the combustion process in an engine is never 100% efficient, leaving behind hot, yet unburned hydrocarbons. Oxidizer fitted to a carâ„¢s tailpipe rapidly oxidizes a large percentage of the remaining unburnt hydrocarbons, resulting in cleaner emissions. However, the speed at which catalytic oxidizers must operate to catch unburnt hydrocarbons before they fly out the tailpipe puts limits on how efficient the oxidation process can be.
3.2 EU emission standards for petrol vehicles.
standards NOx (g/kWh) HC (g/kWh) PM (mg/kWh)
Euro I (1992-93) 9.0 1.23 400
Euro II 1995-96) 7.0 1.1 150
Euro III (2000) 5.01 0.662 100/1603
Euro IV (2005) 3.51 0.462 20/303
Euro V (2008) 2.01 0.462 20/303
3.3 Evaporative emission control system
The evaporative emission control system is used to prevent emission of fuel vapour.the vapour generated in the fuel tank while driving or the
Engine at a stop passes through a tank pressure control valve and enters the EVAP canister were the charcoal absorbs the stores the fuel vapour. The EVAP canister purge valve is controlled by ECM according to signals from various sensors.
4. SENSORS USED IN MPFI.
1 Manifold absolute pressure (MAP) sensor
This sensor senses pressure change in the intake manifold and converts it into voltage Change. It consists of a semi-conductor type pressure converting element, which converts a pressure change into an electrical change and, an electronic circuit which amplifies and corrects the electric change. The ECM sends a 5-volt reference voltage to the pressure sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes By monitoring the sensor output voltage ,ECM knows the manifold pressure, ECM uses the voltage signal from the pressure sensor as one of the signals to control fuel injector.
2. Throttle position sensor
The throttle position sensor is connected to the throttle valve shaft on the throttle body, and detects throttle valve opening, the throttle opening is detected by the potentiometer. A 5-volt reference Voltage is applied to the sensor from ECM and as Brush moves over the print resistance according
to the throttle valve opening, the output voltage varies accordingly. By monitoring sensor output voltage, ECM detects the throttle valve opening. ECM uses the signal from TP sensor as one of the signals to control various devices.
3 Intake air temperature sensor
Located on the air cleaner outlet hose, this sensor constantly measures the
Temperature of the air entering there and converts a change in the air temperature
Into that in resistance through its thermistor. That is, as is temperature lowers, resistance increases and as it rises, resistance decreases. As air density of the intake air varies with Variation in temperature, ECM, by monitoring the resistance, adjusts the amount of fuel injection according to the air temperature
4 Engine coolant temperature sensor
Incorporated with coolant temperature. Gauge and installed to thermostat case, this sensor measures the temperature of the engine coolant and converts its change into that in resistance through the thermistor like the air temperature sensor, by monitoring the resistance of the coolant temperature sensor, ECM detects the engine coolant temperature and that affects most systems under the control of ECM.
5 Oxygen sensor
The oxygen sensor is installed on the exhaust manifold to detect the concentration of oxygen in the exhaust gases. in order of engines equipped with the three- way catalytic converter to achieve their best exhaust emission purification performance, it is necessary for the air-fuel ratio to be kept within a narrow range near the theoretical air-fuel ratio The oxygen sensor senses whether the air-fuel ratio is richer on leaner than the theoretical air-fuel ratio, The oxygen sensor is located in the exhaust manifold and consists of an element made of zirconium dioxide (zrO2, a kind of ceramic material) Ã‚Â¬This element is coated on both inside and outside with a thin layer of platinum. Atmospheric air is introduced into the inside of the sensor, and outside of the sensor is exposed to the exhaust gases. If the Oxygen concentration on the inside surface of the zirconium element differs greatly from that on the outside surface at high temperatures, the zirconium element generate a voltage when the air-fuel mixture is lean there is lot of oxygen in the exhaust gas, so there is a little difference between oxygen concentration inside and outside the sensor element. Thus the voltage generated by the zirconium element is low if the air-fuel mixture is rich; the oxygen in the exhaust has almost disappears. This creates a large difference in the oxygen concentrations inside and outside the sensor and voltage generated by the zirconium element is large. The ECM uses this signal to increase or reduce the injection volume to keep the air-fuel ratio at an even value near the stoichiometric air-fuel ratio.
6 Vehicle speed sensor
The vehicle speed sensor, located on the transmission gearbox or speedometer, Generates a signal in proportion to the vehicle speed. Receiving this signal, the speedometer uses it for operation of its indicator and also converts it into to the ON/OFF signal by doubling the cycle. This signal is sent to ECM where it is used as one of the signals to control various devices.
7. Camshaft position sensor
The sensor is mounted on the sensor case (distributor less ignition case) on tile camshaft let side for distributor less ignition vehicle and other vehicles on the distributor. The signal rotor is press-fitted onto the camshaft (distributor less ignition vehicle) and other vehicles on the distributor shaft. As the sensor has a built-in hall element and a waveform forming circuit, it converts changes in the magnetic flux caused by rotation of the signal rotor into electric pulse signals, Using this signal and the signal from the CKP sensor (if equipped), ECM identifies the cylinder whose piston is in the compression stroke.
8. Crank shaft position sensor
The sensor consists of magnet and coil. It is mounted on oil pan with specified air gap between the sensor core end and crankshaft timing belt pulley tooth. As the crankshaft turns, AC voltage is generated in the sensor. ECM uses this signal as: Engine speed, Cylinder identification.
5. ADVANTAGES OF MPFI
1) More uniform A/F mixture will be supplied to each cylinder; hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this the life of engine components is improved.
(2) No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system.
(3) Immediate response, in case of sudden acceleration / deceleration.
(4) Since the engine is controlled by ECM* (Engine Control Module), more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level.
(5) The mileage of the vehicle will be improved.
Almost all vehicles in India are changing to the mpfi because of law emissions, improved mileage and drivability since the engine is controlled by micro computer more accurate amount of a/f mixture will be supplied and as a result complete combustion will take place. this leads to effective utilization of fuel supplied and hence low emission level. it reduces wastage of fuel by the use of sensors and other control systems
Automotive technology â€œJack erjavec
Automobile engineering â€œ Anil chhakra