Patent Application
20070175452
The present invention relates to internal combustion engines, and more particularly to a combustion control for reducing engine emissions.
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. The additional exhaust gas affects the amount of engine air intake through the throttle. EGR is the most efficient means to reduce overall emissions. Large amounts of EGR (e.g., up to 60%) may be necessary to sufficiently reduce the emissions to meet regulatory requirements.
During transient maneuvers, the required amount of EGR and the actually achieved EGR may differ as a result of delays in the engine system. In some cases, the difference could be quite significant, which can result in an unacceptable increase in emissions (i.e., NOx and HC) during transient maneuvers.
Accordingly, the present invention provides an engine control system that includes an exhaust gas recirculation (EGR) valve. The engine control system further includes a first module that determines an EGR error and a second module that calculates a fuel injection timing based on the EGR error. Operation of an engine is regulated based on the fuel injection timing to reduce emissions during transient operation of the engine.
In other features, the second module calculates the fuel injection timing based on a time constant and a base fuel injection timing. The engine control system further includes a third module that determines the time constant based on the EGR error. The base fuel injection timing is determined based on an engine speed and torque.
In still other features, the first module determines the EGR error based on an EGR set-point and an estimated EGR. The engine control system further includes a third module that determines an EGR estimate based on a mass air flow (MAF) and a charge flow (CF). The MAF is determined using a MAF sensor and the CF is determined based on an engine speed, a manifold absolute pressure (MAP), an intake manifold temperature and a volumetric efficiency of the engine.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
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Air is drawn into the intake manifold 14 through a throttle 25 and a filter 27. Air is drawn into the cylinders 20 from the intake manifold 14 and is compressed therein. Fuel is injected by the injection system 16 and the air/fuel mixture is combusted within the cylinders 20. The exhaust gases are exhausted from the cylinders 20 and into the exhaust system 18. In some instances, the engine system 10 can include a turbo 26 that pumps additional air into the cylinders 20. In such a system, the turbo 26, which is driven by the exhaust gas, compresses the air and the compressed air flows through the throttle 25.
The exhaust system 18 includes an exhaust manifold 30, an exhaust conduit 31, an EGR valve 34, an EGR conduit 35 and an EGR cooler 36. The exhaust manifold 30 directs the exhaust from the cylinder banks 22, 24 into the exhaust conduit 31. The EGR valve 34 selectively re-circulates a portion of the exhaust through the EGR conduit 35, as explained in further detail below. The remainder of the exhaust is directed into the turbo 26 to drive the turbo 26. The exhaust stream flows from the turbo 26 to an exhaust after-treatment system (not illustrated).
A control module 42 regulates operation of the engine system 10 based on the combustion control of the present invention. More specifically, the control module 42 controls operation of both the fuel injection timing (i.e., the point at which fuel is injected into a cylinder relative to a crank angle and a piston position within the cylinder) and the EGR valve 34. The control module 42 communicates with an intake manifold absolute pressure (MAP) sensor 44 and an engine speed sensor 46. The MAP sensor 44 generates a signal indicating the air pressure within the intake manifold 14 and the engine speed sensor 46 generates a signal indicating engine speed (RPM). The control module 42 determines an engine load based on the RPM and fueling rates. The control module 42 also communicates with a mass airflow (MAF) sensor 47 that generates a MAF signal and an intake manifold temperature sensor 49 that is responsive to the intake manifold air temperature (TIM).
The combustion control of the present invention regulates the EGR valve 34 and the fuel injection timing to minimize emission excursions during transient engine operation. As used herein, the term transient refers to a transition in engine operation from a first steady-state condition to a second steady-state condition. The combustion control adjusts the fuel injection timing based on an EGR error (EGRERR). EGRERR is calculated as the difference between an estimated actual EGR rate (EGREST) and a set-point EGR rate (EGRSP). EGREST is estimated based on the difference of MAF and an estimated charge flow (CF). MAF is measured directly using the MAF sensor 47. CF is calculated using a speed-density relationship as a function of TIM, MAP, engine RPM and the volumetric efficiency (VEFF) of the engine. EGRSP is determined based on engine RPM and torque using a pre-determined look-up table stored in memory.
The combustion control determines a base injection timing (INJBASE) from a main injection timing schedule. More specifically, INJBASE is determined based on engine RPM and torque using a pre-determined look-up table stored in memory. An actual injection timing (INJACT) is determined based on INJBASE and EGRERR. More specifically, a timing constant (kTIME) is determined based on EGRERR using a pre-determined look-up table stored in memory. kTIME is applied to INJBASE using dynamics such as filtering. For example, time-variable first order filter can be applied to INJBASE using kTIME to determine INJACT. In this manner, no additional timing calibration is required. Alternatively, INJACT can be determined from a pre-determined look-up table based on EGRERR and INJBASE, and a filter can be applied to the table output.
When operating in steady-state, the filter does not affect INJBASE, whereby INJACT is equal to INJBASE. However, when transient, the filter adjusts INJBASE to provide INJACT. In this manner, the Combustion control of the present invention automatically determines when the engine is operating in transient state.
Fuel injection timing is a more rapid engine operation actuator as compared to EGR and has sufficient control authority to affect HC and NOx during deviations of EGREST from EGRSP. As a result, active and efficient reduction of emissions is enabled using INJACT as the control parameter based on EGRERR. Further, the combustion control of the present invention is operable throughout the entire engine operating region and eliminates the need for switching logic between different modes of combustion (e.g., low temperature combustion, diffusion combustion, partial HCCl combustion) by providing seamless transitions therebetween.
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Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.
