Control method of a direct injection system of the common rail type provided with a high-pressure fuel pump
A control method of a direct injection system of the common rail in an internal combustion engine; the control method contemplates the steps of: feeding the pressurized fuel to a common rail by means of a high-pressure pump presenting at least one pumping element mechanically operated by a drive shaft of the internal combustion engine; measuring the angular position of the drive shaft; measuring the fuel pressure in the common rail; analyzing the oscillations of the fuel pressure in the common rail; and determining the phase of the pumping element of the high-pressure pump with respect to the drive shaft according to the oscillations of the fuel pressure in the common rail.
1. A control method of a direct injection system of the common rail in an internal combustion engine; the control method comprises the steps of:
feeding the pressurized fuel to a common rail by means of a high-pressure pump presenting at least one pumping element mechanically operated by a drive shaft of the internal combustion engine;
measuring the angular position of the drive shaft;
measuring the fuel pressure (P rail ) in the common rail;
analyzing the oscillations of the fuel pressure (P rail ) in the common rail; and
determining phase of the pumping element of the high-pressure pump with respect to the drive shaft according to the oscillations of the fuel pressure (P rail ) in the common rail when there is no injection;
wherein the step of determining the phase of the pumping element of the high-pressure pump with respect to the drive shaft comprises the further steps of: determining the angular position of the drive shaft at which the fuel pressure (P rail ) in the common rail reaches a relative maximum; and determining the angular position of the drive shaft at which the TDC of the pumping element occurs according to the angular position of the drive shaft at which the fuel pressure (P rail ) in the common rail reaches a relative maximum; and
wherein the step of determining the angular position of the drive shaft in which the fuel pressure (P rail ) in the common rail reaches a relative maximum comprises the further steps of: determining a variation model of the fuel pressure (P rail ) in the common rail according to the position of the pumping element of the high pressure pump; detecting a sequence of measurements of the fuel pressure (P rail ) in the common rail during a pumping cycle by correlating the corresponding angular position of the drive shaft at the time of the measurement to each measurement; and estimating the angular position of the drive shaft at which the fuel pressure (P rail ) in the common rail reaches a relative maximum using the variation model of the fuel pressure (P rail ) combined with the measurements of the fuel pressure (P rail ).
2. A control method according to claim 1 , and comprising the further steps of:
feeding the fuel to the high-pressure pump by means of a shut-off valve;
cyclically controlling the opening and the closing of the shut-off valve for choking the flow rate of fuel taken in by the high-pressure pump itself;
adjusting the flow rate of fuel taken in by the high-pressure pump by varying the ratio between the duration of the opening time and the duration of the closing time of the shut-off valve; and
driving the shut-off valve synchronously with the mechanical actuation of the high-pressure pump and thus with the revolution of the drive shaft.
3. A control method according to claim 2 , and comprising the step of phasing the driving of the shut-off valve with respect to the mechanical actuation of the high-pressure pump so that the opening of the shut-off valve is given at a desired angular position with respect to the mechanical actuation of the high-pressure pump and thus with respect to the drive shaft.
4. A control method according to claim 2 , and comprising the further steps of:
determining at least one critical angle of the high-pressure pump; and
phasing the driving of the shut-off valve with respect to the mechanical actuation of the high-pressure pump and thus with respect to the rotation of the drive shaft so that the opening control of the shut-off valve is given outside the critical angle of the high-pressure pump.
5. A control method according to claim 1 , wherein the phase of the pumping element is determined during a phase of pressurization of the common rail when the internal combustion engine is started.
6. A control method according to claim 1 , wherein the phase of the pumping element is determined during a cut-off phase of the internal combustion engine.
7. A control method according to claim 6 , wherein the phase of the pumping element is determined during a cut-off phase of the internal combustion engine only when the fuel pressure (P rail ) in the common rail is higher than a given predetermined threshold value.
8. A control method according to claim 6 , wherein the phase of the pumping element is determined during a cut-off phase of the internal combustion engine only when revolution speed of a drive shaft is comprised in a predetermined measurement range.
9. A control method according to claim 1 , wherein the angular position of the drive shaft at which the TDC of the pumping element occurs is estimated according to the angular position of the drive shaft at which the fuel pressure (P rail ) in the common rail reaches a relative maximum.
10. A control method according to claim 1 , wherein the angular position of the drive shaft at which the TDC of the pumping element occurs is estimated according to the angular position of the drive shaft at which the fuel pressure (P rail ) in the common rail reaches a relative maximum corrected by an angular correction value.
11. A control method according to claim 10 , wherein the angular correction value is constant and predetermined.
12. A control method according to claim 10 , wherein the angular correction value is variable according to the rotation speed of the drive shaft, to the fuel pressure (P rail ) in the common rail and/or to a fuel flow rate (m Leak ) lost by leakage from the common rail.
13. A control method according to claim 1 , wherein the variation model of the fuel pressure (P rail ) in the common rail is represented by the following equations:
ⅆ
P
rail
ⅆ
t
=
k
b
V
r
·
(
m
HP
=
m
inj
-
m
leak
-
m
Backflow
)
[
2
]
m
HP
=
η
·
V
p
2
·
∫
θ
0
π
sin
θ
(
t
)
ⅆ
t
[
3
]
P rail is the fuel pressure in the common rail;
k b is the fuel bulk module;
V r is the volume of the common rail;
m HP is the fuel flow rate from the high-pressure pump;
m Leak is the fuel flow rate lost by leakage;
m Inj is the injector fuel flow rate in cylinders of the injectors;
m Backflow is the fuel flow rate drawn by the injectors for their actuation and discharged into the discharge channel;
V p is the volume of each pumping element of the high-pressure pump;
η is the efficiency of the high-pressure pump;
θ 0 is the beginning of the delivery angle;
θ is the rotation angle of the high-pressure pump.