3356174 - INTRODUCTION - PETROL FUEL INJECTION SYSTEM

SPECIFICATIONS

GENERAL SPECIFICATIONS

The Bosch Motronic ME7.3H4 system (with a microhybrid technology control unit) with a motorized throttle belongs to the category of ignition systems integrated with phased, sequential type electronic injection.The fuel supply system is the returnless type.The control unit electronically controls the air flow rate at the rotation speed set by the electronic throttle, regulates the fuel injection so that the (air/fuel) ratio is always within the optimum value, calculating the moment of ignition, in order to allow the smooth operation of the engine when the environmental parameters and loads applied vary.The ignition system is the static advance type with a single coil with four outlets. The power modules are housed inside the control unit.The self-adaptive type engine management system is capable of recognizing the changes that take place in the engine and of compensating for them using the self-adaptive functions that correct the carburation and air flow plans mapped in the control unit.There are two adaptive functions, in particular, for the carburation plan depending on whether the evaporation control solenoid valve is open or closed plus an idle adaptation plan: the latter is capable of compensating effectively for any air seepage.The continuous self-adaptation of the carburation plan makes it possible to ensure the correct amount of fuel in all temperature and altitude conditions.As a result of this, after every intervention it is necessary to drive the vehicle for at least 15 minutes in various operating conditions in order to memorize any changes that have taken place in the system in the control unit and end the adaptation.

The main system functions are essentially as follows:

  • injection time adjustment;
  • ignition advance adjustment;
  • cold starting check control;
  • check on enrichment during acceleration;
  • fuel cut-off during deceleration;
  • idle speed management (also dependent on battery voltage);
  • restriction of the maximum engine speed;
  • combustion control with Lambda sensor;
  • petrol vapour recovery;
  • fan control;
  • climate control system engagement/disengagement;
  • self-diagnostics.

There is also a special function that manages the connection with the body computer via a two-way signal for the CAN line that includes:

  • engine temperature for instrument panel (output);
  • battery voltage (output);
  • engine rpm (output) for instrument panel;
  • engine overheating warning light for instrument panel (output);
  • engine oil pressure warning light for panel (output);
  • vehicle speed (input) + milometer (input);
  • Fiat code anti-theft device (input/output);
  • key status;
  • consumption signal (output) for trip computer.
  • fuel level signal (input)

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.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 amount of fuel depending on the desired mixture strength.The other sensors in the system (coolant temperature, throttle valve position, battery voltage, etc.) allow the electronic control unit to correct the basic strategy for all the 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 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 special maps in accordance with:

  • engine rpm
  • absolute pressure value (mmHg) measured in the intake manifold.
This advance value is corrected depending on the temperature of the engine coolant, intake air, detonation and throttle position.The spark plugs for the cylinders are connected directly to the coil secondary winding terminals (one per spark plug).

OPERATION

Diagram showing information entering/leaving the control unit

The information entering/leaving the control unit is illustrated in the diagram below.
1, Engine management control unit2, Battery3, Ignition switch4, Engine control system relay5, Electric fuel pump relay6 , Fuel pump7, Radiator fan relay(s)8, Radiator fan9, Compressor engagement relay10, Compressor11, Ignition coils12, Spark plugs13, Injectors14, Carbon filter scavenging solenoid15, Lambda sensor (pre-catalyzer)16, Lambda sensor (post-catalyzer)17, Coolant temperature sensor18, Detonation sensor19, Throttle control actuator and throttle position sensor20, Rpm and TDC sensor21, Injection timing sensor22, Air temperature/absolute pressure sensor23, Oil pressure switch24, Body computer:25, CODE control unit (via CAN)26, Diagnostic equipment connection (via CAN)27, Rev counter (via CAN)28, System failure lamp (via CAN)29, Speedometer (via CAN)30, City button for driving assistance (via CAN0

SELF-LEARNING

The control unit implements the self-learning logic in the following conditions: *- removing-refitting or replacing the injection control unit *- removing-refitting or replacing the throttle casingThe values stored by the control unit are maintained when the battery is disconnected.

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 strategy is as follows.The warning light comes on with the ignition on and remains on until the engine is started up; the control unit autodiagnostic system checks the signals coming from the sensors comparing them with the permitted data 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.

SYSTEM CONTROLS AND MANAGEMENT

Fiat code recognition

The moment the control unit receives the ignition ON signal it converses with the body computer to obtain the go ahead for starting.The communication takes place via the two-way CAN line that connects the two control units.

Cold starting check

The following occurs in cold starting conditions:

  • a natural weakening of the mixture (which causes poor turbulence of the particles of fuel at low temperatures)
  • reduced evaporation of the fuel
  • fuel condensation on inner walls of the intake manifold
  • higher 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.The rotation speed decreases proportionally as the engine temperature increases until the nominal value is reached when the engine has warmed up.

Combustion - lambda sensor check

In EOBD systems, the Lambda sensors are all the same type and located upstream of the catalytic conversion system and downstream of the converter.The pre-catalyzer sensor determines the control of the mixture strength known as the 1st closed loop for the upstream sensor.The post-catalyzer sensor 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 pre-catalyzer sensor responses could experience due to ageing and contamination.This control is known as 2nd loop control (post-catalyzer sensor closed loop).

Knock control

The control unit detects the presence of detonation (engine knock) by processing the signal coming from the relevant sensor.The control unit continuously compares the signals coming from the sensor with a threshold which is, in turn, continually updated to take into account background noise and engine ageing.The control unit is therefore capable of detecting the presence of detonation (or the onset of detonation) in each individual cylinder and reduces the ignition advance in the cylinder involved (in steps of 3° up to a maximum of 6°) until the phenomenon disappears. Later on, the advance is gradually restored to the basic value (in steps of 0.8°).In acceleration conditions, a higher threshold is used to take into account the increased noise of the engine in these circumstances.The detonation control logic also has a self-adjustment function which memorizes the reductions in the advance that are continuously repeated in order to adapt the map to the different conditions that the engine finds itself in.

Check on enrichment during acceleration

In this stage the control unit increases the amount of fuel supplied to the engine (to produce the maximum torque) depending on the signals coming from the following components:

  • throttle potentiometer
  • rpm and TDC sensor
The 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 control unit reopens the injector (extra pulse) in order to be able to adjust the mixture strength as quickly as possible; the subsequent injections
... DATA ERROR - CROPPED TEXT | Ошибка данных - Текст обрезан ...