Method of controlling fuel injection
A method of controlling fuel injection in an internal combustion engine having at least one cylinder with an associated electrically actuated fuel injector for performing injection events, wherein a drive signal is applied to the fuel injector in order to actuate a needle therein that controls flow through a valve seat. The drive signal comprises a fueling pulse adapted to move and/or hold the needle to an open position relative to a valve seat, followed by a braking pulse adapted to slow down the needle moving towards a closed position relative to the valve seat, the braking pulse being separated from the fueling pulse by a separation period. The braking pulse is configured to end at a timing that substantially matches the moment when the needle reaches the closed position.
1 . A method of controlling fuel injection in an internal combustion engine having at least one cylinder with an associated electrically actuated fuel injector for performing injection events, wherein a drive signal is applied to the fuel injector in order to actuate a needle therein that controls flow through a valve seat;
wherein the drive signal comprises a fueling pulse adapted to move and/or hold the needle to an open position relative to a valve seat, followed by a braking pulse adapted to slow down the needle moving towards a closed position relative to the valve seat, the braking pulse being separated from the fueling pulse by a separation period;
wherein the braking pulse is configured to end at a timing that substantially matches the moment when the needle reaches the closed position, the braking pulse ending within ±50 μs of the moment when the needle reaches the closed position.
2 . The method according to claim 1 , wherein the separation period is calibrated on the basis of a nominal closing time or a learned closing time of the needle.
3 . The method according to claim 2 , wherein the needle closing time is learned for the respective fuel injector during engine operation.
4 . The method according to claim 3 , wherein the needle closing time is derived from the injector voltage trace.
5 . The method according to claim 2 , wherein the needle closing time is learned during a learning mode, during which the drive signal does not include a braking pulse.
6 . The method according to claim 1 , wherein the braking pulse has a predetermined energy calibrated in function of a respective engine operating point.
7 . The method according to claim 6 , wherein the braking pulse has a predetermined duration read from a map in function of fuel pressure and flow rate.
8 . The method according to claim 6 , wherein the braking pulse has a predetermined current intensity read from a map in function of fuel pressure.
9 . The method according to claim 1 , wherein the separation period is read from a map in function of fuel pressure and flow rate.
10 . The method according to claim 2 , wherein the needle closing time is read from a map in function of fuel pressure and flow rate.
11 . The method according to claim 6 , wherein the braking pulse energy is determined by optimizing to reach a desired target closing speed for a respective operating point with the lowest increase of needle closing time and lowest energy.
12 . The method according to claim 1 , wherein the duration of the separation period is determined by a positioning routine comprising:
for a given operating point, performing a plurality of injection events while increasing the separation period; and
selecting the optimal value of separation period based on the analysis of the voltage trace corresponding to each drive pulse.
13 . The method according to claim 12 , wherein a characteristic parameter is derived from the voltage trace and used for selecting the optimal value of separation period, the characteristic parameter reflecting the needle closing time.
14 . The method according to claim 12 , wherein the optimal separation period is determined by comparison to a threshold.
15 . The method according to claim 13 , wherein the characteristic parameter is a glitch magnitude.
16 . The method according to claim 15 , wherein the optimal separation period is determined based on a drop in glitch magnitude.
17 . A fuel injection control unit configured to perform the steps of the method of controlling fuel injection as claimed in claim 1 .