Control method of an electronic injection fuel feeding system

1. A control method of an electronic injection fuel feeding system ( 12 ) for an internal combustion engine ( 1 ) and including at least one injector ( 13 ) and a non-continuous flow rate fuel pump ( 14 ) actuated by a an actuator device ( 27 ); the control method including the steps of:

determining the desired fuel amount (M fuel ) which must be injected at each cycle of the internal combustion engine ( 1 );

driving the injector ( 3 ) for injecting the desired fuel amount (M fuel ) at each cycle of the internal combustion engine ( 1 ) and at an injection frequency (F inj ) depending on the rotation speed of the internal combustion engine ( 1 );

determining an optimal pumping frequency (F pump ) of the actuator device ( 27 ) of the fuel pump ( 14 ) according to the desired fuel amount (M fuel ) which must be injected at each cycle of the internal combustion engine ( 1 ); and

actuating the actuator device ( 27 ) of the fuel pump ( 14 ) at the optimal pumping frequency (F pump );

the control method is characterized in that it includes the further steps of:

determining in a design phase, a lower threshold value (Th 1 ) and a higher threshold value (Th 2 );

comparing the desired fuel amount (M fuel ) with the two threshold values (Th 1 , Th 2 );

assigning to the optimal pumping frequency (F pump ) a value which is independent from the injection frequency (F inj ) when the desired fuel amount (M fuel ) is lower than the lower threshold value (Th 1 ) or when the desired fuel amount (M fuel ) is higher than the higher threshold value (Th 2 ) in order to drive the fuel pump ( 14 ) in an asynchronous manner with respect to the driving of the injector ( 3 ); and

assigning to the optimal pumping frequency (F pump ) the same value of the injection frequency (F inj ) when the desired fuel amount (M fuel ) is comprised between the two threshold values (Th 1 , Th 2 ) in order to drive the fuel pump ( 14 ) in a synchronous manner with respect to the driving of the injector ( 3 ).

2. Control method according to claim 1 , wherein the lower threshold value (Th 1 ) is approximately equal to 10% of the maximum fuel amount which can be injected at every cycle of the internal combustion engine ( 1 ), and the higher threshold value (Th 2 ) is approximately equal to 50% of the maximum fuel amount which can be injected at every cycle of the internal combustion engine ( 1 ).

3. Control method according to claim 1 and comprising the further step of assigning to the optimal pumping frequency (F pump ) a constant value which is independent from the actual value of the desired fuel amount (M fuel ) when the desired fuel amount (M fuel ) is lower than the lower threshold value (Th 1 ).

4. Control method according to claim 1 and comprising the further step of assigning to the optimal pumping frequency (F pump ) a variable value which depends on the desired fuel amount (M fuel ) when the desired fuel amount (M fuel ) is higher than the higher threshold value (Th 2 ).

5. Control method according to claim 1 , wherein the optimal pumping frequency (F pump ) is always lower than the injection frequency (F inj ) when the desired fuel amount (M fuel ) is lower than the lower threshold value (Th 1 ).

6. Control method according to claim 1 , wherein the optimal pumping frequency (F pump ) is always higher than the injection frequency (F inj ) when the desired fuel amount (M fuel ) is higher than the higher threshold value (Th 2 ).

7. A control method according to claim 1 and including the further step of phasing the actuation of the actuator device ( 27 ) of the fuel pump ( 14 ) with the driving of the injector ( 3 ) so that, to the greatest possible extent, the pumping stroke of the fuel pump ( 14 ) occurs when the injector ( 3 ) injects the fuel.

8. A control method according to claim 7 and including the further steps of:

determining the start of the fuel injection; and

determining the start of the actuation of the actuating device ( 27 ) of the fuel pump ( 14 ) by applying a predetermined advance with respect to the start of the fuel injection.

9. Control method according to claim 7 and comprising the further steps of:

making the pumping of the fuel pump 14 take place when the injector 3 injects the fuel if the desired fuel amount (M fuel ) is comprised between the two threshold values (Th 1 , Th 2 ) and when the desired fuel amount (M fuel ) is lower than the lower threshold value (Th 1 ); and

making part of the pumpings of the fuel pump 14 take place when the injector 3 injects the fuel if the desired fuel amount (M fuel ) is higher than the higher threshold value (Th 2 ).

10. A control method according to claim 1 and including the further step of varying the actuation of the actuator device ( 27 ) of the fuel pump ( 14 ) according to a battery voltage.

11. A control method according to claim 1 , wherein the feeding system ( 12 ) includes a connection pipe ( 16 ), which hydraulically connects the fuel pump ( 14 ) to the injector ( 13 ); the control method includes the further step of actuating the actuator device ( 27 ) of the fuel pump ( 14 ) at the maximum possible pumping frequency (F pump ) and for a predetermined number of times for pressurizing the connection pipe ( 16 ) when the fuel pump ( 14 ) is electrically supplied.

12. A control method according to claim 11 and including the further step of actuating the actuator device ( 27 ) of the fuel pump ( 14 ) at a predetermined maintenance frequency immediately after the step of actuating at the maximum possible pumping frequency (F pump ) and until the internal combustion engine ( 1 ) is started.

13. A control method according to claim 1 , wherein the feeding system ( 12 ) includes a driving device ( 38 ) which supplies electric power to the actuator device ( 27 ) of the fuel pump ( 14 ); the driving device ( 38 ) includes:

an energizing transistor ( 39 ), which connects a first terminal ( 40 ) of the actuator device ( 27 ) to an electric ground ( 41 )/power supply voltage (Vbatt);

an electric connection, which connects a second terminal ( 42 ) of the actuator device ( 27 ) to a power supply voltage (Vbatt)/electric ground ( 41 );

a recirculation transistor ( 43 ), which short-circuit connects the two terminals ( 40 , 42 ) of the actuator device ( 27 ); and

a recirculation diode ( 44 ), which is arranged in series with the recirculation transistor ( 43 ) to avoid a possible short-circuit between electric ground ( 41 ) and power supply voltage (Vbatt).

14. A control method according to claim 13 , wherein the step of actuating the actuator device ( 27 ) of the fuel pump ( 14 ) includes the further steps of:

closing the energizing transistor ( 39 ) so that the current through the actuator device ( 27 ) increases from zero to a peak value (I p );

closing the recirculation transistor ( 43 );

opening the energizing transistor ( 39 ) so that the current through the actuator device ( 27 ) decreases slowly from the peak value (I p ); and

opening the recirculation transistor ( 43 ) to make the current drop rapidly to zero through the actuator device ( 27 ).

15. A control method according to claim 1 , wherein the fuel pump ( 14 ) includes:

a variable volume pumping chamber ( 20 );

a one-way intake valve ( 28 );

a one-way delivery valve ( 24 ); and

a mobile piston ( 21 ) which is coupled to the pumping chamber ( 20 ) to cyclically vary the volume of the pumping chamber ( 2 ) itself and integrates the intake valve ( 28 ) therein;

the actuator device ( 27 ) imparts on the piston ( 21 ) a reciprocating motion and includes an electromagnetic actuator ( 29 ) for actuating the piston ( 21 ) during a step of taking in; and a spring ( 30 ) for actuating the piston ( 21 ) during a step of delivering;

the spring ( 30 ) is dimensioned so that the preloading bias exerted by the spring ( 30 ) on the piston ( 21 ) is equal to the active area of the piston ( 21 ) multiplied by the desired fuel feeding pressure.