223000214 - INTRODUCTION - PETROL FUEL INJECTION SYSTEM
SPECIFICATIONS
The Marelli IAW 5SF3 system belongs the category of systems integrated with:- inductive discharge, digital, electronic ignition- sequential, phased type electronic injection (1-3-4-2).The system in general is illustrated in the diagram.
OPERATION OF THE INJECTION-IGNITION SYSTEM
Main functions
In idling conditions, the control unit controls the following to maintain the smooth running of the engine even when environmental and applied load parameters change:- the moment of ignition- the air flow rate.The control unit controls and manages injection so that stoichiometric air/fuel ratio is always within optimum limits.The system functions are essentially as follows:- system self-adaptation- self-diagnostics- Fiat CODE recognition- cold starting check control- control of combustion - Lambda sensor- detonation control- check on enrichment during acceleration- fuel cut-off during deceleration- fuel vapour recovery- restriction of maximum rpm- fuel supply - electric fuel pump check- connection with climate control system- cylinder position recognition- injection time adjustment- ignition advance adjustment- control and management of idle speed- control of cooling fan- phase transformer control (1.4 8v version only)- vehicle speed control (Cruise Control)- starter motor control.Injection system
The essential conditions to be met by the air-fuel mixture for efficient operation of engines with controlled ignition systems are mainly as follows:- the metering (air/fuel ratio) must be kept as close as possible to stoichiometric value to ensure that combustion is as fast as possible avoiding fuel wastage;- the homogeneity of the mixture, consisting of petrol vapours distributed throughout the air as finely and uniformly as possible.The injection/ignition system uses a measuring system known as "SPEED DENSITY-LAMBDA".In other words, angular rotation speed, density of the intake air and control of the mixture strength.In practice, the system uses the ENGINE SPEED data (rpm) and the AIR DENSITY (pressure and temperature) to measure the quantity of air drawn in by the engine.The quantity of air drawn in by each cylinder, for every engine cycle, also depends on the unit capacity and the volumetric efficiency as well as on the density of the intake air.The density of the air refers to the air drawn in by the engine and calculated according to the absolute pressure and temperature, both measured in the intake manifold.The volumetric efficiency is the parameter relating to the filling coefficient for the cylinders measured on the basis of experiments conducted on the engine for the entire operating range and then stored in the electronic control unit memory.Having established the quantity of intake air, the system must provide the amount of fuel depending on the desired mixture strength.The end of injection impulse or supply timing is stored in a map in the control unit memory and varies according to the engine speed and the pressure in the intake manifold.In practice, it involves processing carried out by the electronic control unit to control the sequential and timed opening of the four injectors, one per cylinder, for the length of time strictly necessary to produce the air/petrol mixture as close as possible to the stoichiometric ratio.The fuel is injected directly into the manifold near the inlet valves at a pressure of around 3.5 bar.Whilst the speed (rpm) and the density of the air (pressure and temperature) are used for measuring the quantity of intake air which, when established, is used for metering the quantity of fuel depending on the desired mixture strength, the other sensors in the system (coolant temperature, throttle valve position, battery voltage) allow the control unit to correct the basic strategy for all engine operating conditions.It is vital for the air/fuel ratio to be close to the stoichiometric value for the correct and prolonged operation of the catalytic silencer and for reducing pollutant emissions.Ignition system
The ignition circuit is the static, inductive discharge type, i.e. without a HT distributor, with power modules located inside the injection -ignition control unit.The system includes two high tension double outlet coils in a single container connected directly to the spark plugs.The primary winding for each coil is connected to the power relay (thereby receiving the battery voltage supply) and to the pins of the electronic control unit for earthing.After the starting stage, the electronic unit manages the basic advance taken from a special map in accordance with:- engine rpm- absolute pressure value (mbar) measured in the intake manifold.This advance value is corrected depending on the temperature of the engine coolant and the intake air.The spark plugs for the cylinders are each connected, by means of a high tension lead, to the secondary winding terminals of each respective coil.This solution is also known as the "single spark" because the energy accumulated by the coil is discharged almost exclusively at the corresponding spark plug electrodes in the cylinder in compression allowing the ignition of the mixture.The coils are housed in a single casing located on the tappet cover.Diagram showing information entering/leaving the control unit
The fuel level and vehicle speed information reaches the control unit via the CAN line. The information relating to the robotized gearbox (where fitted) reaches the injection control unit via the high speed CAN line.
OPERATING LOGICS
System self-adjustment
The control unit is equipped with a self-adjustment function that is designed to recognize the changes that take place in the engine due to the processes of bedding in and ageing of both the components and the engine itself in time.These changes are memorized in the form of modifications to the basic map and are designed to adapt the operation of the system to the gradual alterations in the engine and the components compared with when they were new.This self-adjustment function also makes it possible to compensate for the inevitable differences in any replacement components (due to production tolerances).The control unit modifies the basic map in relation to engine specifications when new on the basis of an exhaust gas analysis.The self-adjustment parameters are not deleted if the battery is disconnected.Autodiagnosis and recovery
The control unit auto-diagnostic system checks that the system is working properly and signals any irregularities by means of an MIL warning light in the instrument panel with a standardized ideogram and colour laid down by European regulations.This warning light indicates engine management faults and also faults detected by EOBD diagnostic strategies.The MIL warning light operating (mil) strategy is as follows:with the ignition on, the warning light comes on and remains on until the engine has been started up.The control unit self-diagnostic system checks the signals coming from the sensors comparing them with the permitted limits.Fault indication during start up:the failure of the warning light to go out when the engine has been started indicates that there is an error memorized in the control unit.Fault indication during operation:- the warning light comes on in flashing mode to indicate possible catalytic converter damage due to misfiring.- the warning light comes on in constant mode to indicate the presence of engine management or EOBD diagnostic errors.From time to time the control unit defines the type of recovery according to the components that are faulty.The recovery parameters are managed by components that are not faulty.Fiat code recognition
The moment the control unit receives the ignition ON signal it converses with the Body Computer (Fiat CODE function) to obtain the go ahead for starting.The communication takes place via the CAN line that connects the two control units.Recognition of cylinder position
The engine timing sensor, together with the engine rpm and top dead centre (TDC) signal, allows the control unit to recognise cylinder sequence when implementing phased injection.This signal is produced by a Hall effect sensor.Combustion - lambda sensor check
In EOBD systems the Lambda sensors, all the same type but not interchangeable, are positioned one before and one after the catalytzer. The sensor upstream of the catalyzer determines the control of the mixture strength known as the 1st closed loop.The sensor downstream of the catalyzer is used for the fault diagnosis of the catalyzer and for modulating the 1st loop control parameters.The second loop is therefore adaptive to make up for production discrepancies and slight drift that the response of the sensor upstream of the catalyzer could experience due to ageing and contamination.This control is known as 2nd loop control (closed loop).Operation when cold
In these conditions there is a natural weakening of the mixture as a result of the poor turbulence of the particles of fuel at low temperature, reduced evaporation and strong condensation on the internal walls of the intake manifold, all of which is exacerbated by the increased viscosity of the lubricant oil which, as is known, increases the rolling resistance of the engine mechanical components at low temperatures.The electronic control unit recognizes this condition on the basis of the coolant temperature signal, increasing the basic injection time.Whilst the engine is warming up, the electronic control unit also operates the stepping motor which determines the quantity of air required to ensure that the engine does not cut out.Operation in full load conditions
The full load condition is detected by the control unit by means of the throttle position and absolute pressure values.In full load conditions the basic injection time must be increased to create the maximum power supply produced by the engine.Operation in deceleration
The engine has two overlapping strategies during this stage:- A negative transition strategy to maintain the quantity of fuel supplied to the engine at the stoichiometric value (less pollution); this stage is recognized by the control unit when the throttle potentiometer signal voltage value goes from a high value to a lower one.- A soft accompaniment strategy at low speed (dash-pot) to dampen the variation in torque supplied (reduced engine braking).Atmospheric correctionAtmospheric pressure varies according to altitude causing a variation in volumetric efficiency such that requires a correction in the basic mixture strength (injection time).The correction of the injection time depends on the variation in altitude and will be automatically updated by the electronic control unit each time the engine is switched off and in certain throttle position and rpm conditions (typically at low engine speeds with the throttle wide open) (dynamic adjustment of atmospheric correction).Cut-off operationThe fuel cut-off strategy is implemented when the control unit recognizes the accelerator released position: pedal percentage = 0% and the engine speed exceeds around 1350 rpm (the value is a guide and varies on the basis of certain parameters, including mainly temperature and gear).The control unit only enables the cut-off when the engine temperature exceeds 0 °C.Recognition that the accelerator pedal is not released or the engine speed is below 1270 rpm (variable guide value for various models) re-enables the engine supply.The cut-off is implemented at very high speeds even if the throttle valve is not completely closed but the pressure in the intake manifold is particularly low (partial cut-off).Operation in acceleration
In this stage the control unit increases the amount of fuel requested by the engine (to produce the maximum torque) depending on the signals coming from the following components:- throttle potentiometer;- rpm and T.D.C. sensorThe basic injection time is multiplied by a coefficient depending on the temperature of the engine coolant, the opening speed of the accelerator throttle and the increase in pressure in the intake manifold.If the sharp variation in the injection time is calculated when the injector is already closed, the co| ... DATA ERROR - CROPPED TEXT | Ошибка данных - Текст обрезан ... |
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