System and method for adaptive control of air-to-fuel ratio
An air-fuel ratio control system includes an internal combustion engine configured to combust gaseous fuel, an admission valve configured to provide gaseous fuel to the internal combustion engine, and a three-way catalyst connected to the internal combustion engine to receive exhaust formed by combustion of the gaseous fuel with the internal combustion engine. The system also includes a sensor connected upstream or downstream of the three-way catalyst and a controller configured to: generate commands for controlling the admission valve, receive oxygen content signals or NOx content signals output from the sensor, and determine, with a perturbation-based control algorithm and based on the oxygen content signals or NOx content signals, commands for controlling an air-fuel ratio of the internal combustion engine, including commands for controlling the admission valve.
1 . An air-fuel ratio control system, comprising:
an internal combustion engine configured to combust gaseous fuel;
an admission valve configured to provide gaseous fuel to the internal combustion engine;
a three-way catalyst connected to the internal combustion engine to receive exhaust formed by combustion of the gaseous fuel with the internal combustion engine;
a sensor connected upstream or downstream of the three-way catalyst; and
a controller configured to:
generate commands for controlling the admission valve,
receive oxygen content signals or NOx content signals output from the sensor, and
determine, with a perturbation-based control algorithm that employs extremum-seeking control and based on the oxygen content signals or NOx content signals, commands for controlling an air-fuel ratio of the internal combustion engine, including commands for controlling the admission valve for adjusting a position of the admission valve according to the extremum-seeking control performed with the controller.
2 . The air-fuel ratio control system of claim 1 , wherein the extremum-seeking control performed with the controller is configured to enable the controller to identify a target air-fuel ratio or a target equivalence ratio.
3 . The air-fuel ratio control system of claim 1 , wherein the perturbation-based control algorithm generates targets for maximizing an objective function or for minimizing a cost function.
4 . The air-fuel ratio control system of claim 1 , wherein the perturbation-based control algorithm is configured to adjust the air-fuel ratio of the internal combustion engine in response to a change in a fuel supplied to the internal combustion engine.
5 . The air-fuel ratio control system of claim 4 , wherein the perturbation-based control algorithm generates outputs that cause a reduction in a quantity of NOx that exits the three-way catalyst, the reduction occurring subsequent to the change in a type of fuel supplied to the internal combustion engine.
6 . The air-fuel ratio control system of claim 1 , wherein the perturbation-based control algorithm generates a first adjustment that causes an increase in the air-fuel ratio and a second adjustment that causes a decrease in the air-fuel ratio, the first adjustment and the second adjustment being repeated to perturb the air-fuel ratio.
7 . The air-fuel ratio control system of claim 1 , wherein the perturbation-based control algorithm is configured to adjust a quantity of oxygen stored with the three-way catalyst.
8 . The air-fuel ratio control system of claim 1 , wherein the perturbation-based control algorithm is applied at multiple intervals of time.
9 . A method for controlling an air-fuel ratio for an internal combustion engine, the method comprising:
receiving oxygen signals output from an oxygen sensor or NOx signals from a NOx sensor;
determining a first air-fuel ratio command;
adjusting, as a first adjustment, the first air-fuel ratio command to increase or decrease a commanded air-fuel ratio;
controlling at least one of: an admission valve, an intake throttle valve, or an exhaust gas recirculation valve based on the first adjustment;
determining a second air-fuel ratio command;
adjusting, as a second adjustment, the second air-fuel ratio command increasing or decreasing the commanded air-fuel ratio, one of the first adjustment or the second adjustment increasing the commanded air-fuel ratio command, the other of the first adjustment or the second adjustment decreasing the commanded air-fuel ratio, the first adjustment and the second adjustment being generated to cause repeating variations in the air-fuel ratio via an algorithm that seeks an objective by making adjustments to commanded air-fuel ratios; and
controlling at least one of: the admission valve, the intake throttle valve, or the exhaust gas recirculation valve based on the second air-fuel ratio command according to adjustments to the commanded air-fuel ratios that are associated with the objective.
10 . The method of claim 9 , wherein the repeating variations are generated as part of an extremum-seeking control algorithm.
11 . The method of claim 9 , wherein, when the first air-fuel ratio command and the second air-fuel ratio command reflect the same air-fuel ratio, the repeating variations prevent controlling the at least one of: the admission valve, the intake throttle valve, or the exhaust gas recirculation to seek the same air-fuel ratio for consecutive commands.
12 . The method of claim 9 , wherein the first air-fuel ratio command corresponds to a desired air-fuel ratio, the first adjustment causing the first air-fuel ratio command to deviate from the desired air-fuel ratio.
13 . The method of claim 9 , wherein the first air-fuel ratio command corresponds to a desired air-fuel ratio, the first adjustment causing the first air-fuel ratio command to deviate from the desired air-fuel ratio by an amount, a magnitude of the amount being based on an objective function or on a cost function.
14 . The method of claim 9 , wherein the air-fuel ratio of the internal combustion engine is adjusted in response to a change in a fuel supplied to the internal combustion engine.
15 . The method of claim 9 , wherein the repeating variations are caused as part of an adaptive control strategy configured to change the air-fuel ratio in response to the internal combustion engine receiving a different fuel type.
16 . A system for controlling an air-fuel ratio for an internal combustion engine, the system comprising:
an internal combustion engine configured to combust fuel;
a valve for providing fuel to the internal combustion engine;
a catalyst connected to the internal combustion engine to receive exhaust formed by combustion of the fuel with the internal combustion engine;
a sensor configured to detect oxygen or NOx present in the exhaust; and
a controller configured to:
generate commands for controlling the valve,
receive signals output from the sensor,
determine a desired air-fuel ratio, and
adjust the desired air-fuel ratio by generating an adjusted air-fuel ratio command that is above or that is below the desired air-fuel ratio as part of an adaptive control strategy that generates fluctuations that change a magnitude and a sign of the adjusted air-fuel ratio command.
17 . The system of claim 16 , wherein the adaptive control strategy employs extremum seeking control.
18 . The system of claim 16 , wherein the valve is an admission valve for providing gaseous fuel to the internal combustion engine.
19 . The system of claim 16 , wherein the controller is further configured to transition from a mode in which the adaptive control strategy is enabled to a mode in which the adaptive control strategy is disabled.
20 . The system of claim 16 , wherein the adaptive control strategy is configured to reduce a magnitude by which the adjusted air-fuel ratio command is above or below the desired air-fuel ratio based on an objective function or a cost function.