Method to determine the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine
A method to determine the oxygen storage capacity of a catalytic converter of an exhaust gas system of an internal combustion engine is described; wherein the exhaust gas system is provided with an exhaust duct, along which catalytic converter is housed; a lambda sensor housed along exhaust duct downstream of catalytic converter to detect the concentration of oxygen in the exhaust gases; and an exhaust gas after-treatment system having a burner designed to introduce exhaust gases into exhaust duct; wherein inside burner there is defined a combustion chamber, which receives fresh air through a first supply circuit and fuel from a second supply circuit. The method comprises a step in which to recognise that internal combustion engine is in a stop phase or in a slow running mode; a step in which to control the first and the second supply circuit so as to obtain a given objective lambda value, in particular other than one; a step in which to determine a delay with which lambda sensor detects the change in objective lambda value; and a step in which to calculate the oxygen storage capacity of catalytic converter by means of said delay.
1 . A method to determine an oxygen storage capacity (OSC) of a catalytic converter of an exhaust gas system of an internal combustion engine; wherein the exhaust gas system comprises:
an exhaust duct, along which the catalytic converter is housed;
a lambda sensor housed along the exhaust duct downstream of the catalytic converter to detect a concentration of oxygen in exhaust gases; and
an exhaust gas after-treatment system having a burner that introduces exhaust gases into the exhaust duct, wherein inside the burner there is defined a combustion chamber, which receives fresh air through a first supply circuit and fuel from a second supply circuit;
the method comprises the steps of:
a) determining whether the internal combustion engine is in a stop phase;
b) controlling the first and the second supply circuit to the burner so as to obtain an objective lambda value (λ OBJ ), other than one;
c) determining a delay with which the lambda sensor detects a change in the objective lambda value (λ OBJ );
d) calculating the oxygen storage capacity (OSC) of the catalytic converter using said delay using formula:
O
S
C
=
M
A
F
*
0.23
*
|
1
-
λ
A
V
G
|
λ
A
V
G
*
D
λ
wherein:
MAF represents the mass flow rate of exhaust gases in a precatalyst;
λ AVG is the average lambda value;
0.23 represents (23%) of oxygen in the air; and
D λ represents the delay of a lambda probe; and
e) controlling the exhaust gas after-treatment system so as to adjust the amount of fresh air in the first supply circuit and the fuel in the second supply circuit so as to achieve the objective lambda value (λ OBJ ) based on the calculated oxygen storage capacity (OSC).
2 . The method according to claim 1 , wherein the first and second supply circuits are controlled to as to obtain an objective lambda value (λ OBJ ) that is greater than 1.
3 . The method according to claim 1 , wherein the first and second supply circuits are controlled to as to obtain an objective lambda value (λ OBJ ) that is smaller than 1.
4 . The method according to claim 1 , wherein the objective lambda value (λ OBJ ) has a step-like development, in which it alternatively is greater than 1 and smaller than 1.
5 . The method according to claim 2 wherein the step of calculating the oxygen storage capacity (OSC) of the catalytic converter using said delay further includes the steps of:
determining a delay (D λL ) of a lean step with which the lambda sensor detects the change in the objective lambda value (λ OBJ ) from smaller than one to greater than one; and
calculating the oxygen storage capacity (OSC) of the catalytic converter using said delay (D λL ) of the lean step.
6 . The method according to claim 4 wherein the step of calculating the oxygen storage capacity (OSC) of the catalytic converter using said delay further includes the steps of:
determining a delay (D λL ) of a lean step with which the lambda sensor detects the change in the objective lambda value (λ OBJ ) from smaller than one to greater than one;
determining a delay (D λR ) of a rich step with which the lambda sensor detects the change in the objective lambda value (λ OBJ ) from greater than one to smaller than one;
calculating an oxygen storage capacity (OSC LEAN ) of the lean step by means of said delay (D λL ) of the lean step;
calculating an oxygen storage capacity (OSC RICH ) of the rich step by means of said delay (D λR ) of the rich step; and
calculating an average value between the oxygen storage capacity (OSC LEAN ) of the lean step and the oxygen storage capacity (OSC RICH ) of the rich step.
7 . The method according to claim 1 further including the steps of:
calculating a plurality of values of the oxygen storage capacity (OSC) of the catalytic converter within a same operating cycle; and
determining an average value of the oxygen storage capacity (OSC) of the catalytic converter.
8 . The method according to claim 1 , further including the step of correcting a value of the oxygen storage capacity (OSC) or an average value of the oxygen storage capacity (OSC) based on a temperature of the catalytic converter.
9 . The method according to claim 1 , wherein prior to the step of controlling the first and the second supply circuit to the burner so as to obtain an objective lambda value (λ OBJ ), heating the catalytic converter so as to reach an operating temperature threshold value.