Method for determining the total pressure in the cylinder of an engine
View Patent ↗A method ( 45 ) for determining the total pressure in a cylinder (P cyl ) of an engine as a function of the angular position (crk) of a crankshaft ( 14 ) and from a quantity of fuel to be injected in possibly several injections, includes: determining the pressure in the cylinder when there is no combustion, the pressure being called the pressure without combustion (P cyl _ m ), determining, for each injection (inj i ), a curve of sub-variation of pressure (ΔP comb _ i ) caused by the combustion of the fuel quantity injected during the such injection (inj i ), the shape of the curve being estimated as a function of the quantity of fuel to be injected (MF i ) and of the angular position for start of injection (SOI i ) of the corresponding injection, determining the total pressure in the cylinder (P cyl ) by adding together the pressure without combustion (P cyl _ m ) and the pressures given by the pressure sub-variation curves (ΔP comb _ i ) of each injection (inj i ).
1. A method for determining a total pressure in a cylinder (P cyl ) of an engine as a function of an angular position (crk) of a crankshaft ( 14 ) and from a quantity of fuel to be injected in possibly several injections, and for controlling a quantity of fuel injected into the engine, the method comprising:
determining the pressure in the cylinder when there is no combustion, said pressure being called the pressure without combustion (P cyl _ m ),
determining, for each injection (inj i ), a curve of sub-variation of pressure (ΔP comb _ i ) caused by a combustion of the fuel quantity injected during the injection (inj i ) in question, a shape of the curve being estimated as a function of the quantity of fuel (MF i ) to be injected and of an angular position for start of injection (SOI i ) of the corresponding injection,
determining the total pressure in the cylinder (P cyl ) by adding together the pressure without combustion (P cyl _ m ) and the pressures given by the pressure sub-variation curves (ΔP comb _ i ) of each injection (inj i ),
adjusting an injector opening duration based on the total pressure of the cylinder.
2. The method as claimed in claim 1 , wherein the pressure without combustion (P cyl _ m ) is determined by considering that a compression and an expansion of the gas mixture contained in the cylinder are adiabatic and that said mixture behaves like an ideal gas, said determination being linearly corrected as a function of a cooling temperature (TCO) and of an exhaust gas recirculation rate (EGR).
3. The method as claimed in claim 1 , wherein each pressure sub-variation curve (ΔP comb _ i ) is determined by a relationship between a combustion efficiency (η), the quantity of fuel to be injected (MF i ), a volume of the cylinder relative to the angular position (crk) of the crankshaft ( 14 ), the combustion start slope (σ i ) of the pressure sub-variation curve (ΔP comb _ i ), an angular position for the start of combustion (SOC i ) of the crankshaft ( 14 ), a combustion end slope (α i ) of the pressure sub-variation curve (ΔP comb _ i ) and an angular position for the end of combustion (EOC i ) of the crankshaft ( 14 ).
4. The method as claimed in claim 3 , wherein the combustion efficiency (η) is determined from a base value (ctse η ) which is corrected as a function of a cooling temperature of the fuel (TCO i ) and of a pressure of the fuel (FUP i ) at injection.
5. The method as claimed in claim 3 , wherein each combustion start slope (σ i ) is determined from a base value (ctse σ ) which is corrected as a function of the quantity of fuel to be injected (MF i ), an exhaust gas recirculation rate (EGR) and a time (T DIFFi ) between a previous injection (inj i-1 ) and the corresponding injection (inj i ).
6. The method as claimed in claim 3 , wherein the angular position for start of combustion (SOC i ) of the crankshaft is determined by adding together the angular position for start of injection (SOI i ) and a time constant (τ i ) which is, itself, determined from a base value (ctse τ ) which is linearly corrected as a function of the quantity of fuel to be injected (MF i ) and of an exhaust gas recirculation rate (EGR).
7. The method as claimed in claim 3 , wherein the combustion end slope (α i ) is determined by a linear relationship as a function of the angular position for start of injection (SOI i ).
8. The method as claimed in claim 3 , wherein the angular position for end of combustion (EOC i ) is determined by a linear relationship between the angular position for start of combustion (SOC i ), a rate of the combustion (λ) and the quantity of fuel to be injected (MF i ).
9. A device for determining a total pressure of an engine cylinder (P cyl ) as a function of an angular position (crk) of a crankshaft ( 14 ), comprising:
means for determining the pressure in the cylinder when there is no combustion, said pressure being called the pressure without combustion (P cyl _ m ),
means for determining, for each injection (inj i ), a curve of sub-variation of pressure (ΔP comb _ i ) caused by a combustion of the fuel quantity injected during the injection (inj i ) in question, a shape of the curve being estimated as a function of the quantity of fuel (MF i ) to be injected and of an angular position for start of injection (SOI i ) of the corresponding injection,
means for determining the total pressure in the cylinder (P cyl ) by adding together the pressure without combustion (P cyl _ m ) and the pressures given by the pressure sub-variation curves (ΔP comb _ i ) of each injection (inj i ).
10. A device for controlling a quantity of fuel to be injected into an engine cylinder as a function of the total pressure in the cylinder (P cyl ), comprising a control unit ( 12 ) in which the device for determining according to claim 9 is installed.
11. The method as claimed in claim 2 , wherein each pressure sub-variation curve (ΔP comb _ i ) is determined by a relationship between a combustion efficiency (η), the quantity of fuel to be injected (MF i ), a volume of the cylinder relative to the angular position (crk) of the crankshaft ( 14 ), a combustion start slope (σ i ) of the pressure sub-variation curve (ΔP comb _ i ), an angular position for the start of combustion (SOC i ) of the crankshaft ( 14 ), a combustion end slope (α i ) of the pressure sub-variation curve (ΔP comb _ i ) and an angular position for the end of combustion (EOC i ) of the crankshaft ( 14 ).
12. The method as claimed in claim 4 , wherein each combustion start slope (σ i ) is determined from a second base value (ctse σ ) which is corrected as a function of the quantity of fuel to be injected (MF i ), an exhaust gas recirculation rate (EGR) and a time (T DIFFi ) between a previous injection (inj i-1 ) and the corresponding injection (inj i ).
13. The method as claimed in claim 4 , wherein the angular position for start of combustion (SOC i ) of the crankshaft is determined by adding together the angular position for start of injection (SOI i ) and a time constant (τ i ) which is, itself, determined from a second base value (ctse τ ) which is linearly corrected as a function of the quantity of fuel to be injected (MF i ) and of an exhaust gas recirculation rate (EGR).
14. The method as claimed in claim 5 , wherein the angular position for start of combustion (SOC i ) of the crankshaft is determined by adding together the angular position for start of injection (SOI i ) and a time constant (τ i ) which is, itself, determined from a second base value (ctse τ ) which is linearly corrected as a function of the quantity of fuel to be injected (MF i ) and of an exhaust gas recirculation rate (EGR).
15. The method as claimed in claim 4 , wherein the combustion end slope (α i ) is determined by a linear relationship as a function of the angular position for start of injection (SOI i ).
16. The method as claimed in claim 5 , wherein the combustion end slope (α i ) is determined by a linear relationship as a function of the angular position for start of injection (SOI i ).
17. The method as claimed in claim 6 , wherein the combustion end slope (α i ) is determined by a linear relationship as a function of the angular position for start of injection (SOI i ).
18. The method as claimed in claim 4 , wherein the angular position for end of combustion (EOC i ) is determined by a linear relationship between the angular position for start of combustion (SOC i ), a rate of the combustion (λ) and the quantity of fuel to be injected (MF i ).
19. The method as claimed in claim 5 , wherein the angular position for end of combustion (EOC i ) is determined by a linear relationship between the angular position for start of combustion (SOC i ), a rate of the combustion (λ) and the quantity of fuel to be injected (MF i ).
20. The method as claimed in claim 6 , wherein the angular position for end of combustion (EOC i ) is determined by a linear relationship between the angular position for start of combustion (SOC i ), a rate of the combustion (λ) and the quantity of fuel to be injected (MF i ).