184000273 - INTRODUCTION - PETROL INJECTION SYSTEM

SPECIFICATIONS

GENERAL CHARACTERISTICS

The Bosch Motronic ME73H4 system (microhybrid control unit) with a motorized throttle belongs to the category of ignition systems integrated with sequential timed electronic injection system.The fuel system is returnless.The control unit electronically controls the air flow rate (flow meter) at the rotation speed set through the electronic butterfly, it regulates the fuel injection so that the (air/fuel) ratio is always within the optimum values, calculating the moment of ignition, in order to allow the smooth operation of the engine as the environmental parameters and loads applied vary.The ignition system is the static advance type with one coil with four outlets. The power modules are located inside the control unit.The engine control system, which is the auto-adjusting type, is capable of recognizing the changes which take place in the engine and compensates for them according to auto-adjustment functions which correct the carburation and air flow rate plans stored in the control unit.There are also two auto-adjustment functions for the carburation according to the anti-evaporation solenoid valve (see appropriate paragraph) and an idle adjustment plan: the latter is capable of effectively compensating for any air seepage.The continuous auto-adjustment of the carburation makes it possible to have the correct quantity of fuel in all temperature and altitude conditions.As a result of this, after each operation it is necessary to drive the vehicle for at least 15 minutes in the various operating conditions, in order to ensure that the control unit memorizes any changes which have taken place in the system and end the adjustment.

The main operating principles of the system are basically as follows:

  • regulation of injection times;
  • adjustment of ignition advance values;
  • control of cold starting;
  • control of enrichment during acceleration;
  • fuel cut-off during deceleration;
  • management of the idle speed (also according to the battery voltage);
  • limiting the maximum engine speed;
  • control of combustion using the Lambda sensor;
  • fuel vapour recovery;
  • control of the electric fans;
  • attachment/detachment of the climate control system;
  • self test.

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

  • engine temperature for instrument panel (output);
  • battery voltage (output);
  • engine rpm (output) for instrument panel;
  • max engine temperature warning light for instrument panel (output)
  • engine oil pressure warning light for control panel (output);
  • car speed (input) + mileometer (input);
  • Fiat code anti-theft device (input/output);
  • key status;
  • fuel consumption meter signal (output) for trip computer;
  • fuel level gauge signal (input);

Fuel injection system

The essential conditions that must always be met in the preparation of the air-fuel mixture for the correct operation of controlled-ignition engines are mainly:

  • the ''metering'' (air/fuel ratio) must constantly be kept as close as possible to the stoichiometric ratio, so as to ensure the necessary rapidity of combustion, avoiding unnecessary fuel consumption
  • the ''homogeneity'' of the mixture, consisting of petrol vapours, diffused as finely and evenly as possible in the air.
The injection/ignition system uses an indirect measuring system known as the ''SPEED DENSITY LAMBDA'' type.In other words the angular rotation speed, density of the intake air and control of the mixture strength (retroactive control).In practice the system uses data on the ENGINE SPEED (rpm) and 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 each engine cycle depends not only on the density of the intake air, but also on the unit displacement and the volumetric efficiency.The density of the air refers to that of the air drawn in by the engine and calculated according to the absolute pressure and the temperature, both detected in the inlet manifold.Volumetric efficiency refers to the parameter relating to the coefficient for filling the cylinders measured on the basis of experimental tests carried out on the engine throughout the entire operating range and then stored in the electronic control unit memory.Having established the quantity of intake air, the system has to provide the quantity of fuel according to the desired mixture strength.The end of injection pulse or supply timing is contained in a map stored in the control unit memory and varies according to the engine speed and the pressure in the inlet manifold.In practice, it involves processing which the electronic control unit carries out to command the sequential, phased opening of the four injectors, one per cylinder, for the length of time strictly necessary to form the air/petrol mixture which is closest to the stoichiometric ratio.The fuel is injected directly into the manifold near the inlet valve at a pressure of around 3.5 bar.The speed (number of revs per minute) and the density of the air (pressure and temperature) are used to measure the quantity of intake air which, when established, enables the quantity of fuel to be metered according to the desired mixture strength.The other system sensors (coolant temperature, throttle valve position, battery voltage, etc.) allow the control unit to correct the basic strategy for all particular engine operating conditions.It is vital for the air/fuel ratio to be around the stoichiometric value for the correct and prolonged operation of the catalytic silencer and for the reduction of pollutant emissions.

Ignition system

The ignition is of the inductive discharge type, breakerless with power modules located in the electronic injection/ignition control unit.The primary winding for each coil is connected to the power relay (thereby receiving the battery voltage) and to the pins for the electronic control unit for connection to earth.

After the starting stage, the electronic unit manages the basic advance taken from a special map according to the:

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

OPERATION

Diagram of input/output info to/from control unit

The diagram below shows the information entering/leaving the control unit.
1, Engine control unit2, Battery3, Ignition switch4, Engine control system relay5, Fuel pump relay6, Fuel pump7, Radiator fan relay/s8, Radiator fan9, Compressor activation relay10, Compressor11, Ignition coils12, Spark plugs13, Injectors14, Carbon filter flushing solenoid15, Lambda sensor (pre-catalyzer)16, Lambda sensor (post-catalyzer)17, Coolant temperature sensor18, Detonation sensor19, Throttle and throttle position sensor control actuator20, Engine rpm and TDC sensor21, Injection timing sensor22, Air temperature and absolute pressure sensor23, Oil pressure switch24, Body computer25, CODE control unit (via CAN)26, Tester connection (via CAN network)27, Rev counter (via CAN network)28, System failure bulb (via CAN)29, Speedometer (via CAN) and ABS control unit30, City button for power assisted steering (via CAN)

SELF-LEARNING

The control unit implements the self-learning mode in the following conditions:

  • removing-refitting or replacement of the injection control unit
  • removing-refitting or replacement of the throttle body
The values memorized by the control unit are preserved if the battery is disconnected.

SELF-ADAPTATION OF THE SYSTEM

The control unit has a self-adaption function which recognizes changes in the engine which occur as a result of bedding-in and ageing processes of both components and the engine itself.These changes are stored in the form of modifications to the basic mapping, and their purpose is to adapt the operation of the system to the gradual alterations in the engine and components compared with their characteristics when new.This self-adaptation function also makes it possible to even out inevitable differences (due to production tolerances) in any replaced components.From the exhaust gas analysis, the control unit changes the basic mapping in relation to the original characteristics of the new engine.The self-adaptation parameters are not cancelled if the battery is disconnected.

AUTODIANOSIS AND RECOVERY

The control unit autodiagnostic system controls the correct operation of the system and signals any faults by means of an (MIL) warning light in the instrument panel which has a standardized European colour and ideogram.This warning light signals both engine management faults and problems detected by the EOBD strategies.The (MIL) warning light operating logic is as follows:With the ignition key in the ON position, the warning light comes on and remains on until the engine has been started up. The control unit''s self-test system checks the signals coming from the sensors, comparing them with the permitted limits:

Signalling of faults during engine starting:

  • the failure of the warning light to go out once the engine has been started up means that there is an error memorized in the control unit.

Fault indication during operation

  • the warning light flashing indicates possible damage to the catalyzer due to misfire.
  • the warning light constantly on indicates the presence of engine management errors or EOBD errors.
From time to time, the control unit defines the type of recovery according to the components which are faulty.The recovery parameters are managed by those components which are not faulty.

SYSTEM CHECKS AND MANAGEMENT

Recognition of fiat code

When the control unit receives the ignition ''ON'' signal, it communicates with the body computer to obtain starting enablement.Communication takes place via a two-way CAN line which connects the two control units.

Control of cold starting

The following occurs during cold starting:

  • a natural weakening of the mixture because of poor turbulence of the fuel particles at low temperatures
  • reduced fuel evaporation
  • condensation of the fuel on the inner walls of the inlet manifold
  • increased viscosity of the lubricant oil.

The electronic control unit recognizes this condition and corrects the fuel injection time in accordance with:

  • coolant temperature
  • intake air temperature
  • battery voltage
  • engine rpm.
The ignition advance depends solely on the engine rpm and the coolant temperature.The rpm is made to decrease in proportion to the increase in temperature of the engine until the optimum value with the engine up to temperature is obtained.

Control of combustion - lambda sensors

In EOBD systems the Lambda sensors, which are all the same type, are located upstream of the catalyzer and downstream of the catalyzer.The pre-catalyzer sensor carries out the check on the mixture strength called 1st loop (closed loop of the upstream sensor).The post-catalyzer sensor is used for the catalyzer diagnosis and for finely modulating the 1st loop control parameters.With this in mind, the adjustment of the second loop is designed to recover both production differences and those in the response of the pre-catalyzer sensors which may occur as a result of ageing and pollution.This control is known as the 2nd loop (post-catalyzer sensor closed loop).

Control of detonation

The control unit detects the presence of knocking by processing the signal coming from the relevant sensor.The control unit continuously compares the signals coming from the sensor with a threshold value, which, in turn, is continuously updated to take account of background noise and ageing of the engine.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 for the cylinder concerned (in steps of 3 degrees up to a maximum of 6 degrees) until the phenomenon disappears. The advance is then gradually restored to the basic value (in steps of 0.8 degrees).Under acceleration conditions, a higher threshold is used to take account of the increased engine noise under such conditions.The knock control strategy also has a self-adaptation function, which memorizes the reductions in advance that may be repeated continuously, so as to adjust the mapping to the different conditions now affecting the engine.

Control of enrichment during acceleration

During this stage, the control unit increases the quantity of fuel requested by the engine as appropriate (to achieve maximum torque) according to the signals coming from the following components:

  • accelerator pedal potentiometer and throttle position.
  • rpm and TDC sensor
The ''basic'' injection time is multiplied by a coefficient which depends on the temperature of the engine coolant, the opening speed of the accelerator butt
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