Air fuel ratio control system for internal combustion engines

A fuel control system of an engine system comprises a pre-catalyst exhaust gas oxygen (EGO) sensor and a control module. The pre-catalyst EGO sensor determines a pre-catalyst EGO signal based on an oxygen concentration of an exhaust gas. The control module determines at least one fuel command and determines at least one expected oxygen concentration of the exhaust gas. The control module determines a final fuel command for the engine system based on the pre-catalyst EGO signal, the fuel command, and the expected oxygen concentration.

FIELD

The present disclosure relates to engine control systems, and more particularly to fuel control systems for internal combustion engines.

BACKGROUND

A fuel control system reduces emissions of a gasoline engine. The fuel control system may include an inner feedback loop and an outer feedback loop. The inner feedback loop may use data from an exhaust gas oxygen (EGO) sensor arranged before a catalytic converter of the engine system (i.e., a pre-catalyst EGO sensor) to control an amount of fuel sent to the engine.

For example, when the pre-catalyst EGO sensor senses a rich air/fuel ratio in an exhaust gas (i.e., non-burnt fuel vapor), the inner feedback loop may decrease a desired amount of fuel sent to the engine (i.e., decrease a fuel command). When the pre-catalyst EGO sensor senses a lean air/fuel ratio in the exhaust gas (i.e., excess oxygen), the inner feedback loop may increase the fuel command. This maintains the air/fuel ratio at true stoichiometry, or an ideal air/fuel ratio, improving the performance (e.g., the fuel economy) of the fuel control system.

The inner feedback loop may use a proportional-integral control scheme to correct the fuel command. The fuel command may be further corrected based on a short term fuel trim or a long term fuel trim. The short term fuel trim may correct the fuel command by changing gains of the proportional-integral control scheme based on engine operating conditions. The long term fuel trim may correct the fuel command when the short term fuel trim is unable to fully correct the fuel command within a desired time period.

The outer feedback loop may use information from an EGO sensor arranged after the converter (i.e., a post-catalyst EGO sensor) to correct the EGO sensors and/or the converter when there is an unexpected reading. For example, the outer feedback loop may use the information from the post-catalyst EGO sensor to maintain the post-catalyst EGO sensor at a required voltage level. As such, the converter maintains a desired amount of oxygen stored, improving the performance of the fuel control system. The outer feedback loop may control the inner feedback loop by changing thresholds used by the inner feedback loop to determine whether the air/fuel ratio is rich or lean.

Exhaust gas composition affects the behavior of the EGO sensors, thereby affecting accuracy of the EGO sensor values. As a result, fuel control systems have been designed to operate based on values that are different than those reported. For example, fuel control systems have been designed to operate “asymmetrically,” (i.e., the threshold used to indicate the lean air/fuel ratio is different than the threshold used to indicate the rich air/fuel ratio).

Since the asymmetry is a function of the exhaust gas composition and the exhaust gas composition is a function of the engine operating conditions, the asymmetry is typically designed as a function of the engine operating conditions. The asymmetry is achieved indirectly by adjusting the gains and the thresholds of the inner feedback loop, requiring numerous tests at each of the engine operating conditions. Moreover, this extensive calibration is required for each powertrain and vehicle class and does not easily accommodate other technologies, including, but not limited to, variable valve timing and lift.

SUMMARY

A fuel control system of an engine system comprises a pre-catalyst exhaust gas oxygen (EGO) sensor and a control module. The pre-catalyst EGO sensor determines a pre-catalyst EGO signal based on an oxygen concentration of an exhaust gas. The control module determines at least one fuel command and determines at least one expected oxygen concentration of the exhaust gas. The control module determines a final fuel command for the engine system based on the pre-catalyst EGO signal, the fuel command, and the expected oxygen concentration.

A method of operating a fuel control system of an engine system comprises determining a pre-catalyst EGO signal based on an oxygen concentration of an exhaust gas; determining at least one fuel command; determining at least one expected oxygen concentration of the exhaust gas; and determining a final fuel command for the engine system based on the pre-catalyst EGO signal, the fuel command, and the expected oxygen concentration.

DETAILED DESCRIPTION

To reduce calibration costs associated with conventional fuel control systems, the fuel control system of the present disclosure allows for direct achievement of desired behavior, including asymmetric behavior. In other words, the fuel control system achieves the desired behavior through open loop control instead of closed loop control. Open loop control may include using a model that relates the desired behavior to a fuel command needed to achieve the desired behavior instead of a calibration of closed loop control gains.

In addition, because the fuel control system achieves the desired behavior through open loop control, other control objectives are achieved. For example, fuel commands from several different objectives (e.g., maintaining an amount of oxygen stored in a catalytic converter) are added to a current fuel command, improving the performance of the fuel control system. In another example, the fuel control system accommodates different powertrains (e.g., powertrains with heated oxygen sensors and/or wide range sensors) and vehicle classes.

Referring now toFIG. 1, an exemplary implementation of an engine system10is shown. The engine system10includes an engine12, an intake system14, a fuel system16, an ignition system18, and an exhaust system20. The engine12may be any type of internal combustion engine with fuel injection. For example only, the engine12may include fuel injected engines, gasoline direct injection engines, homogeneous charge compression ignition engines, or other types of engines.

The intake system14includes a throttle22and an intake manifold24. The throttle22controls air flow into the engine12. The fuel system16controls fuel flow into the engine12. The ignition system18ignites an air/fuel mixture provided to the engine12by the intake system14and the fuel system16.

An exhaust gas created by combustion of the air/fuel mixture exits the engine12through the exhaust system20. The exhaust system20includes an exhaust manifold26and a catalytic converter28. The catalytic converter28receives the exhaust gas from the exhaust manifold26and reduces toxicity of the exhaust gas before it leaves the engine system10.

The engine system10further includes a control module30that regulates operation of the engine12based on various engine operating parameters. The control module30is in communication with the fuel system16and the ignition system18. The control module30is further in communication with a mass air flow (MAF) sensor32, a manifold air pressure (MAP) sensor34, and an engine revolutions per minute (RPM) sensor36. The control module30is further in communication with an exhaust gas oxygen (EGO) sensor arranged in the exhaust manifold26(i.e., a pre-catalyst EGO sensor38). The control module30is further in communication with an EGO sensor arranged after the catalytic converter28(i.e., a post-catalyst EGO sensor40).

The MAF sensor32generates a MAF signal based on a mass of air flowing into the intake manifold24. The MAP sensor34generates a MAP signal based on an air pressure in the intake manifold24. The RPM sensor36generates a RPM signal based on a rotational velocity of a crankshaft (not shown) of the engine12.

The pre-catalyst EGO sensor38generates a pre-catalyst EGO signal based on an oxygen concentration level of the exhaust gas in the exhaust manifold26. The post-catalyst EGO sensor40generates a post-catalyst EGO signal based on an oxygen concentration level of the exhaust gas after the catalytic converter28. For example only, the EGO sensors38and40may each include, but is not limited to, a switching EGO sensor or an universal EGO (UEGO) sensor. The switching EGO sensor generates an EGO signal in units of voltage and switches the EGO signal to a low or a high voltage when the oxygen concentration level is lean or rich, respectively. The UEGO sensor generates an EGO signal in units of equivalence ratio and eliminates the switching between lean and rich oxygen concentration levels of the switching EGO sensor.

Referring now toFIG. 2, the control module30is shown. The control module30includes a command generator module102, an outer loop module104, and an inner loop module106. The command generator module102determines engine operating conditions. For example only, the engine operating conditions may include, but are not limited, to the rotational velocity of the crankshaft, the air pressure in the intake manifold24, and/or a temperature of engine coolant.

The command generator module102determines a fuel command that will achieve a desired oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a desired fuel). The command generator module102determines the desired oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a desired pre-catalyst EGO). The command generator module102determines the desired pre-catalyst EGO based on a model that relates the desired pre-catalyst EGO to the engine operating conditions. The command generator module102determines the desired fuel based on the desired pre-catalyst EGO.

In another implementation, the command generator module102determines the desired fuel based on a model that relates the desired fuel to engine operating conditions. Either implementation allows for the direct achievement of the asymmetric behavior of the pre-catalyst EGO sensor38. The command generator module102further determines an expected oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a desired fuel EGO). The command generator module102determines the desired fuel EGO based on a model that relates the desired fuel EGO to the desired pre-catalyst EGO. In another implementation, the command generator module102determines the desired fuel EGO based on a model that relates the desired fuel EGO to engine operating conditions.

The command generator module102further determines a fuel command that will mitigate effects of one or more forecastable disruptions (i.e., a mitigation fuel) to achieve the desired pre-catalyst EGO. For example only, a forecastable disruption may be a known error in a base (i.e., current) fuel command of the fuel system16due to an air prediction error. The command generator module102determines the desired pre-catalyst EGO based on a model that relates the desired pre-catalyst EGO to the forecastable disruptions. The command generator module102determines the mitigation fuel based on the desired pre-catalyst EGO.

In another implementation, the command generator module102determines the mitigation fuel based on a model that relates the mitigation fuel to the forecastable disruptions. Either implementation allows for direct achievement of the asymmetric behavior of the pre-catalyst EGO sensor38. The command generator module102further determines an expected oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a mitigation fuel EGO). The command generator module102determines the mitigation fuel EGO based on a model that relates the mitigation fuel EGO to the desired pre-catalyst EGO. In another implementation, the command generator module102determines the mitigation fuel EGO based on a model that relates the mitigation fuel EGO to forecastable disruptions.

The command generator module102further determines a desired oxygen concentration level of the exhaust gas after exiting the catalytic converter28(i.e., a desired post-catalyst EGO). The command generator module102determines the desired post-catalyst EGO based on the engine operating conditions. The desired post-catalyst EGO is equivalent to a desired oxygen storage level in the catalytic converter28.

The outer loop module104receives the desired post-catalyst EGO (i.e., the desired oxygen storage level), the post catalyst EGO, and the pre-catalyst EGO. The outer loop module104estimates an oxygen storage level in the catalytic converter28based on a model that relates the oxygen storage level to the post-catalyst and the pre-catalyst EGOs. The outer loop module104maintains the oxygen storage level at the desired oxygen storage level. This maximizes the efficiency of the catalytic converter28to convert toxins of the exhaust gas to less-toxic substances. To further maintain the oxygen storage level at the desired oxygen storage level, the outer loop module104maintains the post-catalyst EGO at the desired post-catalyst EGO.

When the oxygen storage level is not equal to the desired oxygen storage level or when the pre-catalyst EGO indicates stoichiometry after indicating a lean air/fuel ratio for an predetermined time period, the outer loop module104determines a fuel command that will achieve the desired oxygen storage level (i.e., a storage fuel). The outer loop module104determines the storage fuel based on a model that relates the storage fuel to the estimated oxygen storage level. The outer loop module104further determines an expected oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a storage fuel EGO). The outer loop module104determines the storage fuel EGO based on a model that relates the storage fuel EGO to the estimated oxygen storage level.

The outer loop module104determines a post-catalyst EGO correction factor to minimize an error between the desired post-catalyst EGO and the post-catalyst EGO. The outer loop module104determines a fuel command that will achieve the desired post-catalyst EGO (i.e., a post-catalyst fuel). The outer loop module104determines the post-catalyst fuel based on a model that relates the post-catalyst fuel to the post-catalyst EGO correction factor. The outer loop module104further determines an expected oxygen concentration level of the exhaust gas in the exhaust manifold26(i.e., a post-catalyst fuel EGO). The outer loop module104determines the post-catalyst fuel EGO based on a model that relates the post-catalyst fuel EGO to the post-catalyst EGO correction factor.

The inner loop module106receives the post-catalyst fuel EGO, the post-catalyst fuel, the storage fuel EGO, the storage fuel, the desired fuel EGO, the desired fuel, the mitigation fuel EGO, and the mitigation fuel. The inner loop module106further receives the MAF, the MAP, the RPM, the base fuel, and the pre-catalyst EGO. The inner loop module106determines a fuel correction factor to minimize an error between the pre-catalyst EGO and an expected oxygen concentration level of the exhaust gas in the exhaust manifold26. The expected oxygen concentration level in the exhaust manifold26is a sum of the desired fuel EGO, the mitigation fuel EGO, the post-catalyst fuel EGO, and the storage fuel EGO. To further minimize the error, the inner loop module106modifies the base fuel with the desired fuel, the mitigation fuel, the post-catalyst fuel, and the storage fuel to determine a new fuel command for the fuel system16(i.e., a final fuel).

Referring now toFIG. 3, the command generator module102is shown. The command generator module102includes an engine condition module202, a desired post-catalyst EGO module204, a desired fuel module206, and a desired fuel EGO module208. The command generator module102further includes a forecastable disruption module210, a mitigation fuel module212, and a mitigation fuel EGO module214.

The engine condition module202is an open loop command generator that determines engine operating conditions (e.g., the rotational velocity of the crankshaft). The desired post-catalyst EGO module204receives data on the engine operating conditions and determines the desired post-catalyst EGO based on the engine operating conditions. The desired post-catalyst EGO is equivalent to the desired oxygen storage level (i.e., a desired oxygen storage).

The desired fuel module206receives the data on the engine operating conditions. The desired fuel module206determines the desired pre-catalyst EGO based on the model that relates the desired pre-catalyst EGO to the engine operating conditions. The desired fuel module206determines the desired fuel based on the desired pre-catalyst EGO. In another implementation, the desired fuel module206determines the desired fuel based on the model that relates the desired fuel to the engine operating conditions.

The desired fuel EGO module208receives the data on the engine operating conditions. The desired fuel EGO module208determines the desired pre-catalyst EGO based on a model that relates the desired pre-catalyst EGO to the engine operating conditions. The desired fuel EGO module208determines the desired fuel EGO based on the desired pre-catalyst EGO. In another implementation, the desired fuel EGO module208determines the desired fuel EGO based on the model that relates the desired fuel EGO to the engine operating conditions.

The forecastable disruption module210is an open loop command generator that determines one or more forecastable disruptions (e.g., error in the base fuel). The mitigation fuel module212receives the data on the forecastable disruptions. The mitigation fuel module212determines the desired pre-catalyst EGO based on the model that relates the desired pre-catalyst EGO to the forecastable disruptions. The mitigation fuel module212determines the mitigation fuel based on the desired pre-catalyst EGO. In another implementation, the mitigation fuel module212determines the mitigation fuel based on the model that relates the mitigation fuel to the forecastable disruptions.

The mitigation fuel EGO module214receives the data on the forecastable disruptions. The mitigation fuel EGO module214determines the desired pre-catalyst EGO based on the model that relates the desired pre-catalyst EGO to the forecastable disruptions. The mitigation fuel EGO module214determines the mitigation fuel EGO based on the desired pre-catalyst EGO. In another implementation, the mitigation fuel EGO module214determines the mitigation fuel EGO based on the model that relates the mitigation fuel EGO to the forecastable disruptions.

For some forecastable disruptions, the mitigation fuel module212may take no action, or determine the mitigation fuel to be zero. This mode of operation is desirable for forecastable disruptions that should be ignored by the inner loop module106. For example only, a forecastable disruption that may benefit from this mode of operation is deceleration fuel cut off (DFCO), wherein the fuel system16stops the fuel flow when the engine12decelerates for an extended period of time.

Referring now toFIG. 4, the outer loop module104is shown. The outer loop module104includes an estimated oxygen storage module302, a storage fuel module304, and a storage fuel EGO module306. The outer loop module104further includes a subtraction module308, an outer loop compensator310, a post-catalyst fuel module312, and a post-catalyst fuel EGO module314. The estimated oxygen storage module302receives the post-catalyst and the pre-catalyst EGOs. The estimated oxygen storage module302estimates the oxygen storage level (i.e., an estimated oxygen storage) based on the model that relates the estimated oxygen storage to the post-catalyst and the pre-catalyst EGOs.

The storage fuel module304receives the estimated oxygen storage, the desired oxygen storage, and the pre-catalyst EGO. When the estimated oxygen storage is not equal to the desired oxygen storage or when the pre-catalyst EGO indicates true stoichiometry after indicating a lean air/fuel ratio for an extended period of time, the storage fuel module304determines the storage fuel. The storage fuel module304determines the storage fuel based on the model that relates the storage fuel to the estimated oxygen storage. The storage fuel EGO module306receives the estimated oxygen storage and determines the storage fuel EGO based on the model that relates the storage fuel EGO to the estimated oxygen storage.

The subtraction module308receives the desired post-catalyst EGO and the post-catalyst EGO and subtracts the post-catalyst EGO from the desired post-catalyst EGO to determine a post-catalyst EGO error. The outer loop compensator310receives the post-catalyst EGO error and determines a post-catalyst EGO correction factor based on the post-catalyst EGO error. In various implementations, the outer loop compensator310may determine the post-catalyst EGO correction factor to be equal to the post-catalyst EGO error. Alternatively, the outer loop compensator310may use a proportional-integral control scheme, or other control schemes, to determine the post-catalyst EGO correction factor.

The post-catalyst fuel module312receives the post-catalyst EGO correction factor and determines the post-catalyst fuel. The post-catalyst fuel module312determines the post-catalyst fuel based on the model that relates the post-catalyst fuel to the post-catalyst EGO correction factor. The post-catalyst fuel EGO module314receives the post-catalyst EGO correction factor and determines the post-catalyst fuel EGO based on the model that relates the post-catalyst fuel EGO to the post-catalyst EGO correction factor.

Referring now toFIG. 5, the inner loop module106is shown. The inner loop module106includes a first summation module402, a subtraction module404, a scaling module406, an inner loop compensator408, and a second summation module410. The first summation module402receives the desired fuel EGO, the mitigation fuel EGO, the post-catalyst fuel EGO, and the storage fuel EGO.

The first summation module402sums the desired fuel EGO, the mitigation fuel EGO, the post-catalyst fuel EGO, and the storage fuel EGO to determine the expected oxygen concentration level in the exhaust manifold26(i.e., an expected pre-catalyst EGO). When EGO sensors38,40include typical EGO sensors, summing the desired fuel EGO, the mitigation fuel EGO, the post-catalyst fuel EGO, and the storage fuel EGO may result in too large of a value. If so, the inner loop module106may further include a saturation device (not shown), or other comparable logic, that limits the expected pre-catalyst EGO to an expected range of measurements.

The subtraction module404receives the expected pre-catalyst EGO and the pre-catalyst EGO and subtracts the pre-catalyst EGO from the expected pre-catalyst EGO to determine a pre-catalyst EGO error. The scaling module406receives the pre-catalyst EGO error, the MAF, the MAP, and the RPM. The scaling module406converts the pre-catalyst EGO error (e.g., in units of voltage or equivalence ratio) to an equivalent fuel error that is in the same units.

The scaling module406determines the fuel error based on the pre-catalyst EGO error and the MAF. The fuel error errorfuelis determined according to the following equation:

errorfuel=MAF14.7×errorEGO,(1)
where MAF is the MAF and errorEGOis the pre-catalyst EGO error. In another implementation, the scaling module406determines the fuel error based on the pre-catalyst EGO error, the MAP, and the RPM. The fuel error is determined according to the following equation:
errorfuel=k(MAP, RPM)×errorEGO,
where MAP is the MAP, RPM is the RPM, and k is a function of engine operating conditions as indicated by the MAP and the RPM.

The inner loop compensator408receives the fuel error and determines a fuel correction factor based on the fuel error. In various implementations, the inner loop compensator408may determine the fuel correction factor to simply be equal to the fuel error. Alternatively, the inner loop compensator408may use a proportional-integral control scheme, or other control schemes, to determine the fuel correction factor. The second summation module410receives the fuel correction factor, the desired fuel, the mitigation fuel, the post-catalyst fuel, the storage fuel, and the base fuel. The second summation module410sums the fuel correction factor, the desired fuel, the mitigation fuel, the post-catalyst fuel, the storage fuel, and the base fuel to determine the final fuel.

Referring now toFIG. 6, a flowchart depicts exemplary steps performed by the control module30. Control starts in step502. In step504, the engine operating conditions are determined.

In step506, the desired post-catalyst EGO (i.e., the desired oxygen storage) is determined based on the engine operating conditions. In step508, the desired fuel is determined based on the engine operating conditions. In step510, the desired fuel EGO is determined based on the engine operating conditions.

In step512, the forecastable disruptions are determined. In step514, the mitigation fuel is determined based on the forecastable disruptions. In step516, the mitigation fuel EGO is determined based on the forecastable disruptions.

In step518, the estimated oxygen storage is determined based on the post-catalyst and the pre-catalyst EGOs. In step520, control determines whether the estimated oxygen storage is equal to the desired oxygen storage. If true, control continues in step522. If false, control continues in step524.

In step522, control determines whether the pre-catalyst EGO indicates true stoichiometry after indicating the lean air/fuel ratio for the extended period of time. If true, control continues in step524. If false, control continues in step526.

In step524, the storage fuel is determined based on the desired oxygen storage. In step528, the storage fuel EGO is determined based on the desired oxygen storage. Control continues in step526.

In step526, the post-catalyst EGO error is determined based on the desired post-catalyst and the post-catalyst EGOs. In step530, the post-catalyst EGO correction factor is determined based on the post-catalyst EGO error. In step532, the post-catalyst fuel is determined based on the post-catalyst EGO correction factor.

In step534, the post-catalyst fuel EGO is determined based on the post-catalyst EGO correction factor. In step536, the expected pre-catalyst EGO is determined based on the desired fuel EGO, the mitigation fuel EGO, the post-catalyst fuel EGO, and the storage fuel EGO. In step538, the pre-catalyst EGO error is determined based on the expected pre-catalyst and the pre-catalyst EGOs.

In step540, the fuel error is determined based on the pre-catalyst EGO error and the MAF, or the pre-catalyst EGO, the MAP, and the RPM. In step542, the fuel correction factor is determined based on the fuel error. In step544, the final fuel is determined based on the fuel correction factor, the desired fuel, the mitigation fuel, the post-catalyst fuel, the storage fuel, and the base fuel. Control returns to step504.