939003495 - INTRODUCTION - PETROL FUEL INJECTION SYSTEM
OPERATION OF THE INJECTION-IGNITION SYSTEM
The Bosch Motronic MED7.6.1 system with a motorized throttle belongs the category of systems integrated with:- ignition,- phased sequential electronic injection.The control unit controls the air flow rate at the idling speed set by the electronic throttle.The control unit controls the ignition time, with the benefit of maintaining smooth engine operation even when environmental and applied load parameters change.The control unit controls and manages injection so that stoichiometric air/fuel ratio is always within optimum limits.The main system functions are essentially as follows:- self-learning;- system self-adaptation;- self-diagnosis;- recognition of the Alfa Romeo CODE (immobilizer);- cold starting check control;- control of combustion - Lambda sensors;- phase transformer control;- detonation control;- control of mixture enrichment during acceleration;- fuel cut-off when accelerator pedal is released;- fuel vapour recovery;- control of maximum rpm;- high pressure fuel pump control;- connection with the climate control system;- cylinder position recognition;- control of optimum injection time for each cylinder;- adjustment of ignition advance;- idle speed management (also dependent on battery voltage);- fan control;- connection with ABS/ASR control unit;- connection with the control panel;- fuel system diagnostics;- catalytic converter diagnostics;- misfire detection;- Lambda sensor diagnostics.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 levels to assure maximum catalytic converter conversion capacity (max. efficiency);- the homogeneity of the mixture, consisting of petrol distributed throughout the air as finely and uniformly as possible.Information that the control unit processes to control optimum metering is received by electrical signals emitted by:- air flow meter and air temperature sensor, for the exact quantity of air taken in;- rpm sensor that generates an alternating single-phase signal whose frequency is an indicator of engine rpm;- accelerator pedal with built-in potentiometer to recognize the conditions requested by the driver;- coolant temperature sensor on the thermostat;- Lambda sensors to measure exhaust gas oxygen content.Ignition system
The ignition system is the static, inductive discharge type (i.e. without a high tension distributor).The system has a single coil for each spark plug with an integrated power stage; the advantages of this solution are:- lower electrical overload;- guaranteed constant discharge at each spark plug.At the idle speed only the ignition coils receive a dual pilot signal (two ignitions) and one signal only (single ignition).The control unit contains a memory map with a set of optimum ignition advance values (for the cylinder in combustion phase) that the engine can adopt according to the required speed and engine load.The control unit corrects the advance value mainly on the basis of:- engine coolant temperature;- intake air temperature;- detonation.Information that the control unit processes to operate the single coils is received by electrical signals emitted by:- air flow meter and air temperature sensor, for the exact quantity of air taken in;- rpm sensor that generates an alternating single-phase signal whose frequency is an indicator of engine rpm;- detonation sensor, to recognize the cylinder with detonation and correct the ignition advance;- throtle potentiometer to recognize minimum, partial and full-gas load conditions;- timing sensor.The control unit uses the rpm signal to recognize misfiring that could damage the catalytic converters.Operation
Diagram showing information entering/leaving the control unit
1. Injectors2. Fuel pump3. Air conditioning compressor4. Engine cooling fan5. Cruise Control system control6. Lambda sensor downstream of the catalytic converter7. Air conditioning system gas pressure linear sensor8. Brake pedal switch9. Speedometer signal10. Lambda sensor upstream of the catalytic converter11. Coolant temperature sensor12. Timing sensors13. Detonation sensors14. Fuel pressure sensor15. Rpm sensor16. Accelerator pedal potentiometer17. Flow meter18. Battery19. Clutch pedal switch20. Motorized throttle body21. CAN line22. Alfa CODE23. Diagnostic socket24. Fuel vapour recirculation solenoid valve25. Ignition coils26. Phase transformer solenoid valves27. Injection warning light28. Oil pressure switch29 - Engine rpm signal30 - Fuel pressure regulatorSystem operating logics
Self-learning
The control unit implements the self-learning logic in the following conditions:- installation of a new injection control unit,- installation of a new throttle body actuator integrated with D.V.L.- installation of a new modular intake manifold.The self-learning values for the integrated throttle body with D.V.L. are preserved with the battery disconnected.The learning values for the flywheel for recognizing misfiring are, on the other hand, lost.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.There are two adaptive functions depending on the two intervention plans: minimum and utilization.Self-diagnosis
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 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.RECOVERYFrom 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.Cold starting check
In cold starting conditions, the mixture naturally becomes leaner and this gives rise to low fuel evaporation at low temperatures:- fuel condensation on inner walls of the intake manifold;- increased lubrication oil viscosity.The electronic control unit detects this condition and corrects the injection time on the basis of:- coolant temperature;- intake air temperature;- battery voltage;- engine rpm.The ignition advance is determined solely on the basis of rpm and coolant temperature.During the start-up stage, the control unit sends an initial simultaneous injection command to all injectors (full-group injection). Once cylinder phase has been detected, normal phased sequential operation can begin. At idle speed the injection angle is 45° before T.D.C.; at other speeds the injection angle varies between 310° and 370° before T.D.C. to allow the homogeneity of the mixture.While the engine is warming up, the control unit operates throttle body built into the DVL to modulate the amount of air required to ensure engine revs are high enough to keep the engine running.The rotation speed is decreased as the temperature increases until the rated level is reached with the engine warm.Combustion - lambda sensor check
In EOBD systems, the Lambda sensors are all the same type and are located upstream and downstream of the catalytic converter.The upstream sensors monitor concentration and are known as the 1st loop (closed loop of upstream sensors). During idling the information from the upstream Lambda sensors is not used for correcting the mixture strength.The sensors downstream of the catalytic converter are used to for converter diagnostics and to fine-tune 1st loop control parameters.The second loop is therefore adaptive to make up for production discrepancies and slight drift that upstream sensor responses could experience due to ageing and contamination.This control is known as 2nd loop control (downstream sensors closed loop).Phase transformer control
In order to ensure the optimum quantity of air introduced by the engine, the control unit controls:- the intake timing in two angular positions.The control unit sets the open stage at the maximum torque speed:- cam advance of 25° engine.The control unit sets the closed stage at the maximum power speed:- cam in normal position.The control unit sets the closed stage at the idle speed:- cam in normal position.In the other engine operating conditions, the control unit selects the most suitable configuration for optimum performance, consumption and emissions.Detonation control
The control unit may delay ignition selectively for a particular cylinder on the basis of a combination of parameters received from knock and timing sensors and:- reduce ignition advance in 3° steps to a maximum of 9°;- update the threshold to take into account underlying noise levels and engine ageing.During acceleration, the control unit uses a higher threshold due to the higher engine noise.When the knock disappears, the control unit increases ignition advance in 0.75° steps until recovery is complete.The control unit with a self-adaptive function:- stores advance reductions that are repeated continuously;- adjusts mapping to the various different engine service conditions.RECOVERYIf the timing sensor or knock sensor or injection control unit should fail, a variable ignition delay is implemented on the basis of rpm and engine temperature. Maximum ignition delay is always less than 9° engine.Control of enrichment during acceleration
In cases of high acceleration demand, the control unit modifies injection time and throttle position.RECOVERYThe control unit replaces the signal from the faulty air flow meter with a signal from the potentiometer built into the throttle body actuator integral with the DVL.Fuel cut-off when the accelerator pedal is released
The control unit with:- detection of idling status;- rpm above a certain threshold;deactivates fuel injection on the basis of:- rpm;- engine temperature;- vehicle speed.Before reaching idling level, the rpm descent rate is assessed. If this exceeds a certain level, fuel injection is partially re-activated to ensure that engine rpm drops smoothly to idling level.Once idling speed has been reached, normal functions are resumed.Fuel vapour recovery
Fuel vapours (pollutants) collected in the activated carbon filter (canister) are directed to the intake ports to be burnt.This takes place by means of a solenoid valve operated by the control unit which alternates phases in which it is open (canister scavenging stage) with phases in which it is closed (carburation learning stage).During this opening stage, the opening duty-cycle for the solenoid valve is regulated by the control unit in order to eliminate the fuel vapours without altering the engine carburation.Maximum rpm check
According to the rpm level reached by the engine, the control unit:- above 6800 rpm, cuts off the fuel supply to the injectors (rpm can rise to a peak of 7000 rpm for a period no longer than 5 secs.);- below 6600 rpm, injector operation is resumed.Connection with the climate control system
The compressor takes up power from the engine when the climate control system is activated.When idling, the control unit adjusts air flow to the new power requirement. This offers the benefit of maintaining optimum driveability.The control unit manages the exclusion of the compressor:- over 6500 rpm;- above a set engine coolant temperature threshold (117°C);- upon start-up.Recognition of cylinder position
During each engine revolution, the control unit detects the cylinder in combustion phase: controls the injection and ignition sequence for the appropriate cylinder.If the timing sensor is faulty, the control unit implements the following strategies:- with the engine running, it ensures the engine runs correctly due to its memorized cylinder sequence;- if the engine is turned off and restarted, the ignition is activated for coil pairs with a lost spark. Knock control is deactivated and a fixed delay is applied for all cylinders.Check on optimum injection time for each cylinder
The control unit computes the optimum injection time for each cylinder on the basis of special maps:- it modifies the injection opening start point;- it maintains the closure point determined by the mapping, selected on the basis of rpm;- fuel injection is sequential and phased for each cylinder (S.E.F.I.).Adjustment of ignition advance
The control unit processes the signals coming from the sensors and determines:- ignition advance for each cylinder;- ignition delay for the relevant cylinder (affected by detonation).Idle speed check
The control unit detects idling status when the accelerator pedal is released.The control unit controls the idle speed ignoring | ... DATA ERROR - CROPPED TEXT | Ошибка данных - Текст обрезан ... |
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