General description

GENERAL DESCRIPTION

An electronic control system defines and controls all the parameters of the engine, optimizing performance and consumption through a real time response to the differing operating conditions.

A single control unit governs both ignition and Injection: the point at which the engine catches is identified via special sensors and as a consequence, the actuators carrying out the following functions are operated:

• regulation of injection times;
• regulation of ignition;
• control of cold starting;
• control of enrichment during acceleration;
• fuel cut-off during deceleration;
• constant idle speed control;
• limitation of maximum r.p.m.;
• timing variator control (T.SPARK only);
• combustion control -Lambda probe
• fuel vapour recovery;
• connection with the air conditioner compressor (where applicable);
• connection with the alarm system and with the ALFA ROMEO CODE (where applicable).

The system is also equipped with a self-diagnosis function which memorizes any anomalies and facilitates their identification and correction.

MOTRONIC M 1.7

In comparison to previous models this new 1.7 system employs a control unit of a more technologically up-to-date design and is therefore more reliable. It is also includes various possibilities of operating particular functions.

A "static distribution" electronic ignition has also been adopted (semiconductors without distributor).

The set-up greatly increases reliability as it makes it possible to eliminate rotating components and as a result, reduces noise. In addition sparks are not produced externally, which reduces the risk of interference; it also reduces the number of high voltage cables and connections.

The sensor controlling the throttle valve is also of a new design: the two micro-switches signalling the minimum (throttle valve closed) and maximum (throttle valve open) have been replaced by a potentiometer which sends a signal proportional to the throttle valve angle. The idle speed regulation device is also slightly different and increases the speed of regulation.

The characteristic and innovative feature of this system is the autoadaptation*: it is in fact able to recognize the changes which occur in the engine (internal attrition, settling of the engine with time etc.) so that adjustments can be made as a consequence. This autoadaptation function makes it possible to compensate for the inevitable differences (due to production tolerances) of any replaced components. This permits and optimal results on all vehicles without necessitating particular adjustment and controls.

N.B. Because of this it is important that after any type of intervention the engine is left to run for a few minutes so that the control unit can "memorize" any changes which have taken place and adapt itself to them.

PRINCIPLES OF OPERATION

• Identification of the catch point: the point at which the engine catches is identified by two sensors: the r.p.m amd timing sensor supplies the control unit with the speed and angular position of the crankshaft; the air flow meter supplies the instantaneous volumetric output of the engine (relation between actual volume of air entering the cylinders and the volume of the cylinders themselves).
• Regulation of Injection times (fuel quantity): The control unit controls the injectors at great speed and with great precision, calculating the opening times on the basis of engine loading (r.p.m. and air delivery) also taking battery voltage and engine temperature into account.

Injection is simultaneous; all the injectors are opened at the same time during each revolution permitting the cylinders to be supplied with the correct amount of fuel and improving operation during the transient states

• Regulation of ignition (calculation of advances): a mapping system within the control unit calculates the advance on the basis of engine loading (r.p.m. and air delivery); the value is also corrected on the basis of the intake air temperature and engine temperature.

Ignition is of the static type employing double coils: the set-up which has been adopted exploits the differing pressures and environmental conditions existing at the same time in a pair of cylinders; when one of the cylinders is nearing the firing stage in the presence of air-fuel mixture, the corresponding cylinder is at the end of the exhaust phase in the presence of exhaust gas.

Examining the voltage necessary to strike the arch between the electrodes of the spark plugs it can be noted that in a cylinder during the firing phase this tension is elevated (around 10 kV) while the voltage during the exhaust phase is greatly reduced (around 500 V).

At the moment in which the Motronic control unit removes the control from one of the power phases, the flow of electricity in the main circuit of the relevant coil is interrupted generating, by induction, an increase in voltage on the secondary circuit (up to 30 kV empty).

During the increase in high voltage, one side of the secondary circuit of the coil is closed towards ground by the lost spark which, with a charge of approximately 500 V, strikes the spark plug located in the cylinder during the exhaust phase.