Method for processing a signal of a pressure measuring device inside an internal combustion engine
View Patent ↗A method for processing a signal of a pressure measuring device inside an internal combustion engine, the device including: a pressure measuring sensor supplying an output voltage signal (S B ), and a processing unit connected to the pressure measuring sensor, the method including the following steps: I. calculating a duration (Dt 1 ) between a first time (t 0 ) corresponding to a first combustion pressure peak (P 0 ) and a second time (t 1 ) corresponding to a second combustion pressure peak (P 1 ), consecutive to the first combustion pressure peak (P 0 ), II. calculating a correction start time (t c1 ) defined according to the previously calculated duration (Dt 1 ), III. measuring a value of the signal (V OFF1 ) at the correction start time (t c1 ), IV. correcting the signal, on the basis of the correction start time (t c1 ) in relation to a reference value (V REF ) and obtaining a first processed signal (S) such that: S=S B −V OFF1 +V REF .
1. A method of measuring a pressure in a combustion chamber of a cylinder in a precise manner using a device for processing a signal of a pressure measuring device (D P ) inside an internal combustion engine, said device including:
a pressure measuring sensor ( 800 ) supplying an output voltage signal (S B ) representing the pressure within the internal combustion engine, the signal (S B ) including “plateau” phases during which the voltage changes according to a more or less linear function as a function of time, and voltage peak phases representing the combustion pressure peaks,
a processing unit ( 500 ) connected to said pressure measuring sensor,
the method including the following steps:
I) acquisition of the values of the signal (S B ) by the processing unit ( 500 ),
II) detection by the processing unit ( 500 ) of the voltage peaks of the signal (S B ) representing the combustion pressure peaks,
the method being characterized in that it furthermore includes the following steps:
III) calculation by the processing unit ( 500 ) of a first duration (Dt 1 ) between a first time (t 0 ) corresponding to a first combustion pressure peak (P 0 ) and a second time (t 1 ) corresponding to a second combustion pressure peak (P 1 ), consecutive to the first combustion pressure peak (P 0 ),
IV) calculation by the processing unit ( 500 ) of a correction start time (t c1 ), located in a plateau phase between two combustion peaks, and defined by:
t c1 =t 1± x 1* Dt 1
where:
t c1 is the correction start time,
T 1 is a second time corresponding to a second combustion pressure peak,
Dt 1 is a first duration between the first time (t 0 ) and the second time (t 1 ),
x 1 is a first constant with a value varying between 0.1 and 0.9,
V) measurement by the processing unit ( 500 ) of a value of the signal (V OFF1 ) at the correction start time (t c1 ),
VI) correction by the processing unit ( 500 ) of the signal (S B ), on the basis of the correction start time (t c1 ) in relation to a reference value (V REF ) and obtaining of a first processed signal (S) such that:
S=S B −V OFF1 +V REF
Where S B is the signal at the pressure measuring sensor output,
V OFF1 is the value of the signal at the correction start time (t c1 ),
V REF is the reference value.
2. The method of measuring as claimed in claim 1 , wherein:
during step III: calculation by the processing unit ( 500 ) of a second duration (Dt 2 ) between the second time (t 1 ) corresponding to the second combustion pressure peak (P 1 ) and a third time (t 2 ) corresponding to a third combustion pressure peak (P 2 ), consecutive to the second combustion pressure peak (P 1 ),
during step IV: calculation by the processing unit ( 500 ) of a second correction start time (t c2 ) defined by:
t c2 =t 2+ x 2* Dt 2
Where:
t c2 is a second correction start time,
t 2 is a third time corresponding to a third combustion pressure peak,
Dt 2 is a second duration between the second time (t 1 ) and the third time (t 2 ),
x 2 is a second constant with a value varying between 0.1 and 0.9,
during step V: measurement by the processing unit ( 500 ) of a second value of the signal (V OFF2 ) at the second correction start time (t c2 ), and calculation by the processing unit ( 500 ) of a slope (A), defined by:
A
=
(
V
OFF
2
-
V
OFF
1
)
(
t
c
2
-
t
c
1
)
Where V OFF2 is the value of the signal at the second correction start time (t c2 ),
t c2 is a second correction start time,
during step VI: correction of the signal (S B ) by the processing unit ( 500 ), at a given time (i), located after the second correction start time (t c2 ) and obtaining of a second processed signal (S′) such that:
S ′( i )= S ( i )− A*i
Where S′(i) is the second processed signal at the time i,
S (i) is the first processed signal at the time i.
3. The method of measuring as claimed in claim 2 , wherein the value of the second constant x 2 is equal to the value of the first constant x 1 .
4. The method of measuring as claimed in claim 3 , wherein:
step II comprises the second-order offset of the values of the signal (S B ) in relation to a time unit (t), and obtaining of an offset signal (S D ), such that:
S
D
=
dS
B
2
dt
2
where S D is the offset signal,
step III comprises:
the detection by the processing unit ( 500 ) of two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )] corresponding to the passage of the values of the offset signal (S D ) below a threshold (S 1 ),
the calculation by the processing unit ( 500 ) of a duration (Dt 1 , Dt 2 ) between these two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )].
5. The method of measuring as claimed in claim 2 , wherein:
step II comprises the second-order offset of the values of the signal (S B ) in relation to a time unit (t), and obtaining of an offset signal (S D ), such that:
S
D
=
dS
B
2
dt
2
where S D is the offset signal,
step III comprises:
the detection by the processing unit ( 500 ) of two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )] corresponding to the passage of the values of the offset signal (S D ) below a threshold (S 1 ),
the calculation by the processing unit ( 500 ) of a duration (Dt 1 , Dt 2 ) between these two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )].
6. The method of measuring as claimed in claim 2 , wherein the signal (S B ) is a signal filtered and sampled in relation to the time.
7. The method of measuring as claimed in claim 2 , wherein the value of the first constant x 1 is determined at a maximum engine speed.
8. The method of measuring as claimed in claim 1 , wherein:
step II comprises the second-order offset of the values of the signal (S B ) in relation to a time unit (t), and obtaining of an offset signal (S D ), such that:
S
D
=
dS
B
2
dt
2
where S D is the offset signal,
step III comprises:
the detection by the processing unit ( 500 ) of two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )] corresponding to the passage of the values of the offset signal (S D ) below a threshold (S 1 ),
the calculation by the processing unit ( 500 ) of a duration (Dt 1 , Dt 2 ) between these two consecutive times [(t 0 , t 1 ), (t 1 , t 2 )].
9. The method of measuring as claimed in claim 8 , wherein the value of the threshold (S 1 ) is determined in such a way that, at the detected times (t 0 , t 1 , t 2 ), the value of the signal (P 0 , P 1 , P 2 ) is more or less maximum.
10. The method of measuring as claimed in claim 1 , wherein the signal (S B ) is a signal filtered and sampled in relation to the time.
11. The method of measuring as claimed in claim 1 , wherein the value of the first constant x 1 is determined at a maximum engine speed.
12. The method of measuring as claimed in claim 11 , wherein the maximum engine speed value is 5000 rpm.
13. The method of measuring as claimed in claim 1 , wherein the value of the first constant x 1 varies between 0.4 and 0.7.