RECOVERY
The control unit replaces the signal coming from the faulty air flow meter with the signal from the throttle valve potentiometer.
Fuel cut-off during over-run
During release of the accelerator pedal, and beyond a pre-established threshold, the control unit:
cuts off the supply to the fuel injectors
reactivates the supply to the fuel injectors at 1300-1500 rpm.
As there is no fuel supply, the rpm decreases more or less rapidly depending on the vehicle's driving conditions.
Before idle speed is reached, the trend of the fall in rpm is checked.
If it exceeds a certain value, the fuel supply is partially reactivated so that the engine can 'gently accompany' the drop towards idle speed.
The thresholds for reactivation of the fuel supply and for fuel cut-off vary depending on:
engine coolant temperature
vehicle speed
engine rpm
Fuel vapour recovery
The (polluting) fuel vapours, collected in an activated-charcoal filter (canister), are sent to the inlet ducts to be burnt.
This takes place via a solenoid controlled by the control unit only when the engine's operating conditions so permit.
The control unit compensates for the additional quantity of fuel by reducing the delivery to the fuel injectors.
Control of the maximum rpm
Depending on the rpm reached by the engine, the control unit:
over 6800 rpm cuts off the supply to the injectors (it is permitted to reach a maximum of 7200 rpm for a maximum of 3 secs).
under 6800 rpm resumes driving of the fuel injectors.
Check on fuel-electric fuel pump supply
The control unit supplies the fuel pump:
when the ignition is ON for 0.8 s
with the ignition in the AVV position and the engine speed > 22.8 rpm
The control unit cuts off the supply to the fuel pump:
with ignition in OFF position
with engine speed < 22.8 rpm.
The returnless fuel supply system ensures a constant petrol pressure of 3.5 bar.
Connection to the climate control system
Upon a power demand, following the switching on of the compressor, the control unit drives the idle speed actuator to increase the air flow.
The control unit momentarily interrupts the supply to the compressor:
during starting
by switching it off over 6200 rpm
by switching it off if the engine temperature > 112° C.
during take-off with accelerator fully depressed.
Recognition of cylinder position
During each engine revolution, the control unit recognizes which cylinder is at the power stroke:
it operates the injection and ignition sequence at the appropriate cylinder.
In the absence of the timing sensor signal, the control unit:
deactivates the detonation sensor
with the car moving, maintains phased injection
with the car stopped, controls simultaneous ignition in cylinders 1-4 and 2-3.
Regulation of fuel injection times
The control unit calculates the injector opening times and controls them extremely quickly and precisely on the basis of:
engine load (rpm and air flow)
battery voltage
engine coolant temperature;
Fuel injection is sequential and phased for each cylinder, and takes place at the optimum 'start-of-injection' point, while the 'end-of-injection' point remains fixed.
Torque strategy
The drive by wire systems represent vital tools in satisfying legal requirements such as emissions and fuel consumption in addition to improvements in the driveability of vehicles wih petrol engines (starting, heating, transition response, driving safety, immobilizer, etc.).
The torque for most common petrol engines is mainly affected by the throttle valve which controls the mass of air drawn in by the engine (according to the position of the accelerator pedal) and therefore also the refilling of the cylinder.
In addition to this there are also other parameters which affect the variation of the engine torque: the ignition angle, the air/fuel ratio (Lambda), the deactivation of the injection in certain cylinders, likewise the control of the increase in pressure in engines with turbochargers.
Examples of other elements which affect torque are: the EGR, the adjustment of the camshaft and the switching of the intake manifold.
In recent years the system affecting these parameters has become increasingly complex (including the refilling of the cylinders in the case of electronically controlled throttles), gradually increasing the control and adjustment functions affected by torque (control of idling, the vehicle speed, the transmission, etc.).
From the moment that various elements interact simultaneously, priorities must be established. In any case, since interactions takes place in the individual functions it is not easy to observe the effects on the entire system. If the control values for the torque are recalled directly by one or more systems, the different interactions affect one another reciprocally. This requires a complex adjustment of the information in the control units fitted on the vehicle. There is a strong interdependence between the parameters for the sub-systems which must be calibrated.
The introduction of clutch torque, as the intermediate value torque, represents a decisive step for solving the problem. On the basis of these physical values, it is possible to co-ordinate all the requests before the optimum conversion of the engine control parameters takes place (criteria such as emissions, fuel consumption and protecting components).
STRUCTURE OF TORQUE SYSTEM
With the introduction of a new engine control system, all the torque or output requirements are defined, based on these physical values. This means that the interfaces within the individual functions, like between the (sub) systems, are defined as torque or output, allowing a clear and simple configuration for the system.
External torque request:
driver
cruise control speed
vehicle speed restriction
dynamic control of the vehicle
driveability.
Internal torque request:
engine starting
idle adjustment
engine speed restriction
engine safety.
Output request:
engine starting
catalyzer heating
idle adjustment
output
Torque request:
co-ordination of torque and output requests
conversion of torque
realization of torque request.
Initially all the torque requests are co-ordinated in a central module and reduced to one torque request on the basis of the current engine output requirement.
In addition to the driver's request, the torque requirements for both the engine management system and the pre-set control functions are considered.
Later on, the resulting torque value is converted into a value which affects the torque, the opening of the throttle valve, the injection time, the injection deactivation 'sequence' (the fuel is not introduced into all the cylinder to reduce the torque) and the ignition angle. In addition to this, the exhaust gas emissions and the fuel consumption are also reduced.
Adjustment of ignition advance values
Thanks to the mapping stored in its memory, the control unit can calculate the ignition advance in accordance with:
engine load (idling, choke, full load depending on the rpm and air flow)
intake air temperature
engine coolant temperature
If necessary, ignition can be selectively delayed on any cylinder. This cylinder is identified through a combination of values recorded by the rpm and timing sensors.
Control of the idle speed
The control unit recognizes the idle condition by the accelerator pedal being in the 'released' position.
To control the idle speed according to the consumers switched on and brake/clutch pedal signals, the control unit operates the position of the motorized butterfly.
Idling speed when warm is 840 ± 50 rpm.
Electric engine cooling fan check
The control unit controls the switching on of the electric fan in accordance with the coolant temperature:
temperature for switching on 1st speed 95° C
temperature for switching on 2nd speed 102° C
There is a further check (4 stage pressure switch signal) which engages the 1st or 2nd fan speed, according to the pressure of the refrigerant gas, with the air conditioning system switched on.
In the absence of the coolant temperature signal, the control unit activates the recovery function and switches on the fan 2nd speed until the error disappears.
ME7.3.1 injection/ignition control unit
The control unit is mounted in the engine bay over the throttle body and withstands high temperatures.
The control unit memory is the 'flash EPROM' type, i.e. reprogrammable from the outside without intervening on the hardware.
Replacement of the injection control unit, air capacity case or the throttle body integral with the D.V.E. means that the self-learning procedure has to be carried out.
THROTTLE BODY INTEGRAL WITH D.V.E.
It is fitted on the inlet chamber and regulates the quantity of air drawn in by the engine.
According to the signal coming from the accelerator pedal potentiometer, the injection control unit controls the opening of the throttle by means of a direct current motor integrated in the throttle body integrated with D.V.L.
The throttle opening takes place between 0° and 80° therefore including the idle adjustment.
The throttle body integral with D.V.E. is equipped with two potentiometers integrated so that one controls the other and viceversa.
If both the potentiometers fail or there is no supply, the control unit reduces the engine torque according to the position of the accelerator pedal:
fully depressed, it cuts off the supply to one or more pistons, until a maximum speed of 2500 rpm is reached.
in intermediate positions, it cuts off the supply to one or more pistons, until a speed below 2500 rpm is reached.
If the throttle body integral with D.V.E. or injection control unit is replaced, the 'self-learning' procedure must be carried out 1056B81 run electronic ignition/injection control unit (single) self-learning procedure .
