Coordinated control of throttle and EGR valve

An engine control system that includes a throttle and an exhaust gas recirculation (EGR) valve to regulate a mass air flow (MAF) into an engine includes a first module that determines a MAF control command based on a MAF error. A second module determines an EGR valve position based on the MAF control command and a maximum EGR valve range and the throttle resolution. The throttle is fully open and the EGR valve based on the EGR position when the desired MAF is less than the maximum EGR valve range.

FIELD OF THE INVENTION

The present invention relates to internal combustion engines, and more particularly to a mass airflow control that coordinates operation of a throttle and an exhaust gas recirculation (EGR) valve.

BACKGROUND OF THE INVENTION

Internal combustion engines combust an air and fuel mixture to generate drive torque. More specifically, air is drawn into the engine and is mixed with fuel. The air and fuel mixture is combusted within cylinders to drive a crankshaft, producing drive torque. Mass airflow into the engine and the quantity of fuel injected determine the amount of drive torque generated.

Some engines include exhaust gas recirculation (EGR) systems to improve engine operation and reduce engine emissions. The EGR system includes an EGR valve that regulates an amount of exhaust gas that is circulated back to the intake manifold to be mixed with the air and fuel. The additional exhaust gas affects the amount of engine air intake through the throttle.

One traditional method of controlling engine air intake includes closed-loop EGR valve control and open loop throttle control. The desired throttle position is scheduled based on an open-loop look-up table. The EGR valve is controlled to regulate the mass airflow into the engine. In order to guarantee the set point can be reached under different conditions, the throttle must close more than is necessary, which results in reduced fuel economy due to excessive throttling.

Another traditional method uses closed-loop control of both the EGR valve and the throttle. The EGR valve and the throttle are controlled sequentially. In the low end of the control authority, where EGR valve itself is sufficient to achieve the intake air set point, only the EGR valve is active, which regulates the airflow to the target value while the throttle is fully open. At the high end of the control authority, where the EGR valve by itself is not sufficient to achieve the desired mass airflow, the EGR valve is fully open and the throttle is actuated. This strategy solves the problem of unnecessary throttling, however, it requires a high precision intake throttle valve and position sensor to accurately control the mass airflow.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an engine control system that includes a throttle and an exhaust gas recirculation (EGR) valve to regulate a mass air flow (MAF) into an engine. The engine control system includes a first module that determines a MAF control command based on a MAF error. A second module determines a desired EGR valve position based on the MAF control command and a maximum EGR valve range. The throttle is fully open and the EGR valve is regulated to achieve the desired EGR position when the MAF control command is less than the maximum EGR valve range.

In other features, the second module determines a throttle position based on the MAF control command when the MAF control command is greater than the maximum EGR valve range. The second module determines the EGR position based on the throttle position and the MAF control command.

In still other features, a third module determines the MAF error based on a target MAF and an actual MAF. The target MAF is determined based on an engine RPM and a fuel injection quantity into the engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 1, an exemplary engine system10is schematically illustrated in accordance with the present invention. The engine system10includes an engine12, an intake manifold14, a fuel injection system16and an exhaust system18. The exemplary engine12includes six cylinders20configured in adjacent cylinder banks22,24in V-type layout. AlthoughFIG. 1depicts six cylinders (N=6), it can be appreciated that the engine12may include additional or fewer cylinders20. For example, engines having 2, 4, 5, 8, 10, 12 and 16 cylinders are contemplated. It is further appreciated that the engine12is exemplary in nature an inline-type cylinder configuration is also contemplated.

Air is drawn into the intake manifold14through a throttle25and a filter27. Air is drawn into the cylinders20from the intake manifold14and is compressed therein. Fuel is injected by the injection system16and the air/fuel mixture is combusted within the cylinders20. The exhaust gases are exhausted from the cylinders20and into the exhaust system18. In some instances, the engine system10can include a turbo26that pumps additional air into the cylinders20for combustion with the fuel and air drawn in from the intake manifold14.

The exhaust system18includes an exhaust manifold30, an exhaust conduit31, an EGR valve34, an EGR conduit35and an EGR cooler36. The exhaust manifold30directs the exhaust from the cylinder banks22,24into the exhaust conduit31. The EGR valve34selectively re-circulates a portion of the exhaust through the EGR conduit35, as explained in further detail below. The remainder of the exhaust is directed into the turbo26to drive the turbo26. The exhaust stream flows from the turbo26to an exhaust after-treatment system (not illustrated).

A control module42regulates operation of the engine system10based on the coordinated EGR valve and throttle control of the present invention. More specifically, the control module42controls operation of both the throttle25and the EGR valve34to regulate mass air flow (MAF) into the engine12. The control module42communicates with an intake manifold absolute pressure (MAP) sensor44and an engine speed sensor46. The MAP sensor44generates a signal indicating the air pressure within the intake manifold14and the engine speed sensor46generates a signal indicating engine speed (RPM). The control module42determines an engine load based on the RPM and fueling rates. The control module42also communicates with a mass airflow (MAF) sensor47that generates a MAF signal.

The coordinated EGR valve and throttle control of the present invention regulates the EGR valve34to control the accuracy of the MAF into the engine12while the throttle25is used to extend the control range. Because of the higher precision of the EGR valve34, as compared to the throttle25, accurate control performance is provided even though a coarse precision throttle25is used. While maintaining the control authority of the EGR valve34, the EGR valve position is kept very close to the fully open position to avoid excessive throttling and to improve fuel economy.

An exemplary EGR valve includes an exemplary MAF range of approximately 0.03 kg/s (i.e., at 100% open) to approximately 0.067 kg/s (i.e., at 0% open). The exemplary EGR valve can be adjusted in approximately 0.1% increments with an exemplary MAF change of approximately 0.00003 kg/s per increment (i.e., per 0.1% change in EGR position). It is appreciated, however, that the EGR valve resolution is not always linear to the MAF change between the minimum and maximum EGR positions. An exemplary throttle includes an exemplary MAF range of approximately 0 kg/s (i.e., at 0% closed throttle) to approximately 0.03 kg/s (i.e., at 0% closed throttle). The exemplary throttle can be adjusted in approximately 2% increments with an exemplary MAF change of approximately 0.0006 kg/s per increment (i.e., per 2% change in throttle position). It is appreciated, however, that the throttle resolution is not always linear to the MAF change between the minimum and maximum throttle positions.

MAF corresponds to the fresh air flowing through the throttle25into the engine12. Although only exhaust gas passes through the EGR valve34, the EGR valve34indirectly controls MAF. More specifically, when the EGR valve34is opened, the EGR flow into the engine12increases. Consequently, the MAF is limited/reduced because total fluid flow (i.e., fresh air and exhaust gas combined) into the engine12is nearly constant. When the EGR valve34is fully open (e.g., 100%), the MAF through the throttle25is at its lowest point. If it is desired to further reduce the MAF, the throttle25is moved toward a closed position. In most cases, the throttle25is fully open.

In general, the coordinated EGR valve and throttle control regulates the throttle position (POSTHR) and the EGR valve position (POSEGR) based on a MAF error (MAFERR), which is determined based on a target MAF (MAFTRG) and an actual MAF (MAFACT). MAFTRGis determined from a pre-stored look-up table based on engine RPM and the injected fuel quantity and MAFACTis determined based on the MAF sensor signal. The control outputs are no longer desired MAF, but are command signals to the throttle25and the EGR valve34, which are interpreted as desired positions, in the unit of %, thereof.

The coordinated EGR valve and throttle control initially generates a control signal or MAF control command (MAFCTL) based on a MAFERR. MAFCTLcan vary from 0 to 200%, for example. If MAFCTLis less than the maximum achievable EGR valve range (POSEGRMAX) (e.g., 100%), only the EGR valve34is controlled and the throttle25is fully open. For example, if MAFCTLis 75%, which is less than POSEGRMAXof 100%, POSEGRis set equal to 75% and POSTHRis set equal to 0% closed, which corresponds to a fully open throttle.

If MAFCTLis greater than POSEGRMAXof 100%, the difference between MAFCTLand POSEGRMAX(ΔX) is calculated. POSTHRand POSEGRare determined based on ΔX and the resolution of the throttle25. The position commands are determined in such a way that POSTHRis determined at multiples of the resolution of the throttle25(i.e., any POSTHRvalue finer than the resolution is ignored), and that control of the EGR valve34is based on the residual value. In this manner, POSEGRis less than POSEGRMAXto maintain the control authority of EGR valve34, but is as close as possible to POSEGRMAXto minimize throttling.

For example, if MAFCTLis 124.5%, which is greater than 100%, the throttle25needs to be activated. For an exemplary throttle resolution of 2% (i.e., throttle25is adjusted in 2% increments), POSTHRis set equal to 26%, and POSEGRis set equal to 98.5%. In this manner, the sum of POSTHRand POSEGRequals MAFCTL. For an exemplary throttle resolution of 1% (i.e., throttle25is adjusted in 1% increments), POSTHRis set equal to 25%, and POSEGRis set equal to 99.5%.

Referring now toFIG. 2, exemplary EGR valve position and throttle position traces are illustrated and are based on the coordinated EGR valve and throttle control of the present invention. Initially, the throttle25is fully open, because the EGR valve34is not fully utilized, and the EGR valve34alone regulates mass airflow. When the EGR valve34is fully utilized (i.e., at POSEGRMAX), the throttle25starts to close to extend the operating range of the EGR valve34. While the throttle25is active, the EGR valve34is used to accurately control MAF. Because the throttle25is only controlled at discrete positions, a less expensive, coarse precision throttle is sufficient and does not affect the control performance.

Referring now toFIG. 3, exemplary EGR valve position and throttle position traces using a conventional control are illustrated and are laid over the EGR valve position and throttle position traces ofFIG. 2for comparison purposes. As can be seen, the difference in the EGR valve positions is small (e.g., less than approximately 3%). Similarly, the difference in the throttle positions is also small (e.g., less than the resolution of the coarse precision throttle). As a result, the coordinated EGR valve and throttle control enables use of a less, expensive, coarse throttle and results in less throttling activity.

Referring now toFIG. 4, exemplary steps executed by the coordinated EGR valve and throttle control. In step400, control calculates MAFERRbased on MAFTRGand MAFACT. In step402, control determines MAFCTLbased one engine RPM and fuel injection quantity.

In step406, control determines whether MAFCTLis greater than POSEGRMAX. If MAFCTLis not greater than POSEGRMAX, control sets POSEGRequal to MAFCTLin step408and control ends. In this manner, the throttle25remains fully-open and the EGR valve34is adjusted to achieve POSEGR. If MAFCTLis greater than POSEGRMAX, control determines POSTHRbased on the difference between MAFCTLand POSEGRMAXin step410. In step412, control determines POSEGRbased on the difference between MAFCTLand POSTHRand control ends. In this manner, the throttle25is adjusted to achieve POSTHRand the EGR valve34is adjusted to achieve POSEGR.

Referring now toFIG. 5, exemplary modules that execute the coordinated EGR valve and throttle control will be described in detail. The exemplary modules include a summer500, a PID control module502and a control signal coordination module504. The summer500determines MAFERRas the difference between MAFTRGand MAFACT. The PID control module502determines MAFCTLbased on MAFERR. The control signal coordination module504determine POSEGRand POSTHRbased on MAFCTL. The EGR valve34and the throttle25are controlled to achieve POSEGRand POSTHR, respectively.