244000400 - CONSTRUCTION SPECIFICATIONS

The Marelli 48P.2 system fitted to the 1998 8v engine belongs to the category of integrated systems with digital electronic control via an ignition microprocessor with static advance and distribution and phased indirect intermittent multipoint injection.In this operating mode there are no functional variations in relation to the basic system.The Magneti Marelli 48P.2 basic electronic unit performs in the same way and the system management strategies are the same as for the basic version.The specific elements for the LPG system or the methane system do not, in any way, interfere with the basic system.The Marelli 48P.2 system is able to record a set of parameters via specific sensors or voltage data:engine rpm;the correct cylinder combustion TDC sequence (injection timing);absolute pressure in the intake manifold;intake air temperature;coolant temperature;throttle position and closure/opening speed;presence of oxygen in the exhaust gases;vehicle speed;exhaust gas recirculation solenoid position;the possible presence of detonation;the possible engagement of the air conditioning;the possible power assisted steering end of travel;battery voltagecommunicate with the Metatron METAFUEL 5D0 control unit via a high-speed CAN line.The analogue signals are converted into digital signals by analogue/digital (A/D) converters so that they can be used by the control unit.The control unit memory contains a management program (software) that includes a set of strategies, each of which manages a specific system control function.Each strategy uses the information (input) described above to process a set of parameters based on data maps stored in specific areas of the control unit. The strategy then controls the system actuators (output), i.e.the devices that allow the vehicle to operate, namely:control relays;injectors;ignition coils;actuation solenoids;interface with other control units on the vehicle (LPG or methane, automatic transmission, ABS, speed regulator etc.);interface with the in-car service control unit (in-car computer, climate control system, coded immobiliser).

The MARELLI 48P2 injection-ignition system does not require any adjustment because it is self-adaptive

INJECTION - IGNITION SYSTEM OPERATING DIAGRAM

The following diagram shows the injection - ignition system operating diagram

DIAGRAM SHOWING INFORMATION ENTERING/LEAVING THE CONTROL UNIT

Communcation between the petrol engine management control unit and the LPG or methane engine management control unit takes place via the CAN line.

MAIN MANAGEMENT STRATEGIES

Operating principle

All engine service points can be identified by means of two parameters:rpm;engine load.Once these parameters have been obtained by processing, it is possible to calculate and then implement the injection (amount of fuel delivered and timing with combustion TDC), ignition (correct ignition advance) and any other functions for each engine service point.In the Marelli 48P.2 system, rpm is measured directly by a sensor while engine load is determined indirectly on the basis of absolute pressure and air temperature, both measured in the intake manifold.Specific ignition maps are drawn up during engine and vehicle testing. These store injection time/stage and ignition advance values and all other parameters required for correct engine operation.These values are determined by mathematical extrapolation of parameters for any service point, even points that are not specifically mapped.Calculated injection time values are also corrected on the basis of the signal from the lambda sensor, which determines continuous fluctuation of the mixture content about a stoichiometric level on the basis of specific operating strategies.The system is therefore defined as "speed-density-lambda" type because injection time is mainly determined by these three parameters.All specific operating situations that require specific adaptation of injection time/stage, ignition advance and other calculated parameters are managed by the engine management unit on the basis of signals from various system sensors.

Signal framework mangement

The term "signal framework" denotes the set of signals from a sensor on the crankshaft and a sensor on the camshaft. Because these are related by a specific reciprocal position, they provide the control unit with a synchronised signal sequence that that control unit is able to recognise.During starting the control unit recognizes the injection and ignition timing which are vital for the subsequent operation of all strategies.This recognition is implemented on the basis of the interpretation of the series of signals from the phonic wheel sensor located on the crankshaft and the engine timing sensor on the camshaft.The rpm sensor gives a reference for the angular position of the crankshaft (TDC identification). It is secured to the gearbox bell housing and faces the phonic wheel.This consists of a sealed tubular case containing a permanent magnet and an electric winding or copper coil. It is connected to the electronic control unit via terminals B1 and B2 of connector H32V/C. The wires are twisted 40 coils/metre and covered by a shielded interference-proof sheath connected to earth. A heat-resistant PVC sheath covers leads and shielding.Phonic wheel (3) consists of 58 teeth plus a gap equivalent to the space occupied by the two missing teeth. The reference defined by the space left by the missing teeth constitutes the basis for recording the synchronism point (TDC).The synchronism poinnt is recognised at the end of the first tooth following the gap left by the two missing teeth: when this passes beneath the sensor, the crankshaft is located with piston pair 1-4 at 114° before TDC.Operation is as follows: The sensor permanent magnetic field affects the winding and also the phonic wheel teeth. In practice, when the tooth is in front of the sensor, the magnetic flow is maximum. When the gap passes, the flow is minimum. During phonic wheel rotation, whenever a tooth tends to approach the sensor, the signal rises toward the positive voltage value (+). It becomes zero during the tooth-sensor alignment stage and passes through a negative voltage value (-) as the tooth moves away.The graph and the waveform (which corresponds to the mechanical position of the phonic wheel) is an e.m.f. set up in the sensor winding and may range from a few volts at low rpm to several tens of volts at a high rpm. Because the resulting voltage depends on the distance between sensor core and tooth tip, it is extremely important that this height, known as the GAP is between 0.5 - 1.5 mm.The train of analogue signals generated by the sensor is sent to an appropriate converter circuit (A/D analogue digital) in the electronic control unit (ECU) and used for:calculating the engine rpm;calculating the optimal ignition advance.

Management of the injection

The injection management strategies are designed to provide the engine with the correct amount of fuel at the desired time depending on the engine operating conditions.

Calculating basic injection time

Injection management essentially involves computing injection time, determining injection stage and subsequent implementation of the stage by controlling the injector.Base pulse constant is calculated by mathematical extrapolation from the speed-load map. the experimentally obtained mapped values also depend on injector specifications. The final injection time is determined by means of a calculation algorithm whereby the base pulse constant is corrected by a series of coefficients that take into account the different engine operating conditions.

Cold start-up and running

During cold starting the injection is managed simultaneously (full-group), in other words it is not phased: this situation persists until the engine started. After this, management becomes phased.During cranking by the starter motor, injection time is determined by a special map and depends on coolant temperature and barometric pressure.During cold operation, the base pulse constant is increased as appropriate by a factor inversely proportional to coolant temperature.

Full load

This strategy is enabled when the throttle exceeds a certain threshold: injection time is increased in this situation.

Acceleration and deceleration

The acceleration or deceleration situation represents a transitory state that may be positive (acceleration) or negative (deceleration).The transitory management strategy is very complex: in general, injection time is increased for positive transitories and reduced for negative states.The correction identify depends fundamentally on load and engine speed changes, throttle movement speed and engine temperature.

Cut off

The control unit enables cut off strategies when engine speed exceeds a certain threshold.The cut-off strategy is implemented when the control unit detects the throttle in idle position (throttle potentiometer signal).Engine fuel supply is re-enabled when the throttle is detected in an unclosed position or when speed drops below a threshold higher than the enablement threshold.

Rotation speed limiter

The strategy limits the maximum speed achievable by the engine by enabling cut-off.

Fuel pump drive

The fuel pump is controlled by the engine management unit via the relay.The pump stops:if engine speed drops below a certain minimum threshold;after a certain time (about 5 seconds) with the key ON without start-up taking place (timed enablement);if the inertia switch is operated.

Injector control

Altitude correction

- The control unit detects atmospheric pressure and uses it to make appropriate corrections under the following conditions:- with ignition switch in MAR position,- with engine under high load and with low rpm.The control unit detects atmospheric pressure and uses it to make appropriate corrections under the following conditions:with ignition switch in MAR position,with engine under high load and with low rpm.

Management of the ignition

Ignition management essentially consists of determining the required ignition advance on the basis of engine service conditions and then implementing the advance by controlling a power transistor located inside the control unit. The baseline advance value, calculated on the basis of engine load and speed, is then corrected on the basis of the various engine service conditions. The primary winding of each coil is supplied by battery voltage via a relay and is connected to the power transistor manifold built into the engine control unit. The broadcasting unit is earthed while the base receives control voltage from the control unit.According to engine rotating speed and ignition advance to be implemented, the engine control unit establishes the moment at which conduction begins in the primary winding in order to achieve the required current intensity (saturation) in the primary winding immediately before interrupting the current. The angle of this moment naturally changes in relation to the combustion TDC of each cylinder: its advance is directly proportional to engine rpm because the time required to saturate the current in the coil primary winding is more or less constant: this is determined using appropriate coefficients stored at the mapping stage (dwell management).The conduction start moment is also corrected on the basis of battery voltage.The engine management unit therefore determines the moment at which current is cut off in the primary winding and converts the degrees of advance into the time required by the engine to move through this angle: this time is the advance in relation to combustion TDC with which the current at the base of the transistor is interrupted.At the time when the current interrupts the current at the base of the power transistor, the primary winding earth connection is interrupted and a high tension discharge is therefore triggerd in the secondary coil.

Start-up

During starting, the normal management of the advance cannot be carried out because the considerable fluctuations in the rotation speed do not allow the dwell and the advance to be correctly calculated.The control unit implements a fixed advance throughout the time the engine is cranked by the starter motor.

High temperatures

The base advance value is reduced when intake air temperature exceeds a certain threshold.

Cut off

The injection advance is reduced on entry into cut-off. from the moment the supply of fuel is resumed, the advance is gradually restored to the "basic" value.

Take-off

The strategy reduces advance during vehicle take-off from a standing start.

Engine idling

When the engine is idling, the management of the advance is implemented independently of the "basic" advance.The idling advance value is corrected by a factor inversely proportional to the speed change in relation to a preset speed, in turn dependent upon coolant temperature.In particular, advance is increased if speed drops and is reduced if speed increases to ensure speed stability.

Knock control

This strategy detects the presence of knock effects by processing a signal from the appropriate sensor. The strategy continuously compares a signal from the sensor with a threshold which is in turn continually updated to take into account background noise and engine ageing.If the system detects the presence of knock, the strategy reduces the ignition advance until the effect disappears. The adv

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