Method for measuring the pressure of a compressed gaseous fuel in a supply line of an engine equipping a motor vehicle and associated measuring device

1. A method for measuring pressure of a gaseous fuel compressed in a feed system of an engine equipping a motor vehicle, by a pressure measuring device comprising an infrared quality sensor and an electronic control unit, the measuring method comprising:

determining a composition of the fuel using absorbance measurements made with the infrared quality sensor;

determining a nominal absorbance value from absorbance measurements performed at a nominal pressure, at a first time after the motor vehicle is started and after a phase of stabilization of the fuel pressure, and at preset wavelengths using the infrared quality sensor;

determining a corrected absorbance value of the fuel based on absorbance measurements performed at a second time after the first time, by infrared analysis at the preset wavelengths using the infrared quality sensor; and

determining the pressure of the fuel based on the nominal pressure, the corrected absorbance value, and the nominal absorbance value.

2. The method for measuring pressure according to claim 1 further comprising:

Step E 3 a : measurement and storage of the nominal absorbance value determined based on absorbance measurements made at a first wavelength and at a second wavelength, preset and distinct from one another at a nominal pressure,

Step E 5 a : measurement of at least a first, and a second absorbance value at the first wavelength and at the second wavelength, present and distinct from one another;

Step E 6 a : calculation of the fuel pressure as a function of the nominal pressure, of the nominal absorbance value, of the first and of the second absorbance value.

3. The method for measuring pressure according to claim 1 , wherein

the preset wavelengths comprise a first wavelength λ 1 , second wavelength λ 2 , and a third wavelength λ 3 , preset and distinct from one another.

4. The method for measuring pressure as claimed in claim 2 further comprising, before step E 3 a , performance of the following steps:

Step E 0 : prior storage in memory of the nominal pressure,

Step E 1 : verification of system pressurization, and

Step E 2 : verification that a first preset time has elapsed, otherwise return to step E 1 ,

and, the first preset time corresponds to an average stabilization time of the fuel pressure.

5. The method for measuring pressure as claimed in claim 4 further comprising, between the step E 3 a , and the step E 5 a , the following step:

Step E 4 : verification that a second preset time has elapsed, otherwise return to the step E 1 .

6. The method as claimed in claim 2 , wherein, the first wavelength is such that it is not absorbed by the fuel, and the second wavelength corresponds to the absorption wavelength of methane.

7. The method for measuring pressure as claimed in claim 3 , wherein the third wavelength λ 3 is such that it is distinct from the first wavelength λ 1 and that is not absorbed by the fuel.

8. The method for measuring pressure as claimed in claim 3 further comprising performance of the following steps:

Step E 0 : prior storage in memory of the nominal pressure,

Step E 1 : verification of system pressurization, and

Step E 2 : verification that a first preset time has elapsed, otherwise return to step E 1 .

9. The method for measuring pressure as claimed in claim 8 further comprising the following step:

Step E 4 : verification that a second preset time has elapsed, otherwise return to the step E 1 .

10. The method for measuring pressure according to claim 1 , wherein the pressure of the fuel is determined using the following equation:

P

r

=

P

n

×

Abs

2

⁢

⁢

corr

Abs

n

wherein Abs n is the nominal absorbance value, Abs 2corr is the corrected absorbance value, P n is the nominal pressure, and P r is the pressure of the fuel.

11. The method for measuring pressure according to claim 3 , wherein

the first wavelength λ 1 and the third wavelength λ 3 are located in a spectral zone where the fuel has low or no absorption and the second wavelength λ 2 is located in a spectral zone where the fuel has high absorption.

12. The method for measuring pressure according to claim 3 , wherein

an absorption of the fuel at the third wavelength λ 3 is used to correct variation in a refractive index of the fuel as a function of pressure and wavelength by calculating a value of a coefficient A, wherein A=(Abss3−AbsS1)/(λ 3 −λ 1 ).

13. A device for measuring pressure variations of a gaseous fuel compressed in a feed system of an engine equipping a motor vehicle, the device comprising:

a quality infrared sensor measuring at least at a first wavelength and at second wavelength, preset and distinct from one another; a first and a second absorbance value,

means for detecting pressurization of the system,

a clock,

means for adjusting the wavelength of the quality sensor,

means for storing in memory

a nominal absorbance value, calculated based on absorbance measurements performed at a nominal pressure and taken at a first time after the motor vehicle is started and after a phase of stabilization of the fuel pressure at at least two preset wavelengths using the infrared sensor, and

the nominal pressure,

means for receiving, from the quality sensor, absorbance measurements made at a second time after the first time at the at least two preset wavelengths,

means for determining a composition of the fuel using absorbance measurements made with the infrared quality sensor and computing the pressure of the compressed gas as a function of the nominal absorbance value measured at the first time, the nominal pressure, and corrected absorbance values determined based on the absorbance measurements made at the second time at the at least two preset wavelengths.

14. The device according to claim 13 , wherein the detection means, the clock, the adjustment means, the storage means, the receiving means, and the computing means are included in an electronic control unit.

15. A feed system for gaseous fuel, comprising a pressure measuring device as claimed claim 13 .

16. A motor vehicle comprising a pressure measuring device as claimed in claim 13 .

17. The device according to claim 13 , wherein the at least two preset wavelengths comprise a first wavelength λ 1 , a second wavelength λ 2 , and a third wavelength λ 3 , preset and distinct from one another, and

the first wavelength λ 1 and the third wavelength λ 3 are located in a spectral zone where the fuel has low or no absorption and the second wavelength λ 2 is located in a spectral zone where the fuel has high absorption.

18. The device according to claim 13 , wherein the at least two preset wavelengths comprise a first wavelength λ 1 , a second wavelength λ 2 , and a third wavelength λ 3 , preset and distinct from one another, and

an absorption of the fuel at the third wavelength λ 3 is used to correct variation in a refractive index of the fuel as a function of pressure and wavelength by calculating a value of a coefficient A, wherein A=(Abss3−AbsS1)/(λ 3 −λ 1 ).