Method of determining the injection pattern in the compression stroke of the combustion cycle of the cylinders of a direct-injection internal combustion engine

1. A method of determining the injection pattern in the compression stroke (COMP) of the combustion cycle of the cylinders ( 2 ) of a direct-injection internal combustion engine ( 1 ), the method comprising the steps of:

determining a maximum number (N max _ comp ) of partial injections to be performed in the compression stroke (COMP) and a value of the end of injection angle (EOI);

determining an initial quantity (QF init _ comp ) of fuel to be injected for each partial injection to be performed in the compression stroke (COMP); wherein the initial quantity of fuel (QF init _ comp ) to be injected for each partial injection to be performed during the compression stroke (COMP) is determined as a function of the temperature of the coolant (T coolant _ init ) when the internal combustion engine ( 1 ) is started and as a function of the off time (T off ) of the internal combustion engine ( 1 );

determining an objective quantity (QF obj _ comp ) of fuel to be injected for each partial injection to be performed in the compression stroke (COMP); wherein the objective quantity (QF obj _ comp ) of fuel to be injected for each partial injection to be performed in the compression stroke (COMP) is determined as a function of the speed (V engine ) of the internal combustion engine ( 1 ) and of the load (L engine ) of the internal combustion engine ( 1 ) and of the coolant temperature (T coolant ) of the warm internal combustion engine and of the decay of spark advance (SA) implemented by the internal combustion engine ( 1 );

determining an effective quantity (QF eff _ comp ) of fuel to be injected for each partial injection to be performed in the compression stroke (COMP) as a function of the respective initial quantity (QF init _ comp ) of fuel and of the respective objective quantity (QF obj _ comp ) of fuel;

determining an objective pattern of partial injections to be performed in the compression stroke (COMP) as a function of the value of the end of injection angle (EOI) and of the effective quantity (QF eff _ comp ) of fuel to be injected for each partial injection to be performed in the compression stroke (COMP); and

wherein the effective quantity (QF eff _ comp ) of fuel to be injected for each partial injection to be performed in the compression phase (COMP) is calculated using the following formula:

QF eff _ comp =α*QF obj _ comp +(1−α)* QF init _ comp   [3]

QF eff _ comp effective quantity of fuel to be injected for each partial injection of said maximum number (N max _ comp ) of partial injections to be performed in the compression stroke (COMP);

QF obj _ comp objective quantity of fuel to be injected for each partial injection to be performed in the compression stroke (COMP);

QF init _ comp initial quantity of fuel to be injected for each partial injection to be performed in the compression stroke (COMP); and

α weight ranging from 0 to 1 to be assigned to the objective quantity of fuel to be injected for each partial injection to be performed in the compression stroke (COMP) and variable as a function of the temperature.

2. The method according to claim 1 comprising the further steps of:

determining the minimum quantity (QF min _ comp ) of fuel to be injected for each partial injection in the compression phase (COMP) as a function of the feeding pressure of the fuel upstream of an injector ( 14 ); and

determining an effective pattern of partial injections to be performed in the compression phase (COMP) as a function of the comparison between the minimum quantity (QF min _ comp ) of fuel to be injected for each partial injection in the compression stroke (COMP) and the objective pattern of partial injections to be performed in the compression stroke (COMP).

3. The method according to claim 1 comprising the further step of determining the amount of time elapsing between two subsequent partial injections of the objective pattern to be performed in the compression stroke (COMP) as a function of the value of the end of injection angle (EOI) and of the effective quantity (QF eff _ comp ) of fuel to be injected for each partial injection of said maximum number (N max _ comp ) of partial injections to be performed in the compression stroke (COMP).

4. The method according to claim 1 comprising the further steps of:

determining the overall quantity (Q fuel ) of fuel to be injected for each combustion cycle of each cylinder ( 2 ) to satisfy the request for torque (C) to be delivered which determines the quantity of air that the internal combustion engine ( 1 ) must aspirate;

determining the quantity (Q fuel _ int ) of fuel to be injected for each combustion cycle of each cylinder ( 2 ) during the intake stroke (INT) as a function of the difference between the overall quantity (Q fuel ) of fuel to be injected for each combustion cycle of each cylinder ( 2 ) and the objective pattern of partial injections to be performed in the compression stroke (COMP) for each combustion cycle of each cylinder ( 2 ).

5. The method according to claim 4 comprising the further steps of:

determining the maximum quantity (QF max _ int ) of fuel to be injected for each partial injection in the intake stroke (INT) as a function of the speed (V engine ) of the internal combustion engine ( 1 ), of the load (L engine ) of the internal combustion engine ( 1 ) and of the value of the start of injection angle (SOI); and

determining the number (i) of partial injections of the intake phase (INT) and the objective quantity (QF obj _ int ) of fuel to be injected for each partial injection in the intake stroke (INT) as a function of the quantity (Q fuel _ init ) of fuel to be injected for each combustion cycle of each cylinder ( 2 ) during the intake stroke (INT) and of the maximum quantity (QF max _ int ) of fuel to be injected for each partial injection in the intake stroke (INT).