General description

GENERAL DESCRIPTION

Bosch Motronic M1.5.5 is an electronic system with the following integrated functions:

• induced discharge digital electronic ignition
• static distribution
• timed sequenced electronic injection (1 - 3 - 4 - 2).

When the engine is idling, the unit controls:

• the instant of ignition
• the air intake

thus ensuring the engine is running regularly regardless of the environment conditions or applied loads. The control unit handles injection ensuring that the stoichiometric ratio (i.e. air/fuel ratio) is constantly optimal.

The system functions are, essentially, the following:

• injection timing
• spark advance control
• cold start control
• acceleration enrichment control
• release phase fuel cut-off
• idling control and handling
• maximum rev limitation
• exhaust control - lambda sensor
• cylinder position acknowledgement
• fuel fume re-circulation
• air conditioner connection (where fitted)
• Alfa Romeo CODE (Immobilizer) ECU connection
• system self-adjustment
• self-test
• cooler fan control.

INJECTION SYSTEM

The essential air-fuel mixing conditions for the correct operation of controlled ignition engines are:

• the air/fuel ratio must be appropriately "dosed" and kept as close as possible to the stoichiometric value to ensure fast combustion and avoid unnecessary fuel consumption
• the mix must be "homogenous" i.e. must consist of petrol fumes spread as finely and evenly as possible in the air.

IGNITION SYSTEM

This is a static inductive discharge ignition system (i.e. without high voltage distributor) with power modules located inside the injection ECU. The system consists of a signal coil for each for each spark plug (MONO-COIL). The advantages of this solution are:

• lower electric overload;
• constant discharge on each spark plug.

A map, containing the sequence of optimal spark advance values (for cylinder in explosion stroke) that the engine can adopt according to the required ratio or load, is stored in the ECU memory. The ECU corrects the spark advance mainly on the basis of the following information:

• engine coolant temperature
• inlet air temperature
• knock
• throttle position.

The ECU processes the electric signals from the following devices and pilots the mono-coil:

• the intake air flow meter with integrated temperature sensor, signalling the exact amount of intake air
• the rev sensor, which generates an alternating single phase signal indicating the engine revolution frequency
• knock sensor (on the rear part of the crankcase between cylinders 2° and 3°) to acknowledge which cylinder is exploding and consequently correct spark advance
• the throttle position potentiometer (integrated in the constant idle actuator), indicating minimum, partial and full loads.

For optimal dosing, the ECU processes electric signals transmitted from:

• the intake air flow meter with integrated temperature sensor, signalling the exact amount of intake air
• the rev sensor, which generates an alternating single phase signal indicating the engine revolution frequency
• the throttle position potentiometer (integrated in the constant idle actuator), indicating minimum, partial and full loads
• the lambda sensor, defining the amount of oxygen contained in the exhaust gas.