Diagnostic systems and methods for sensors in homogenous charge compression ignition engine systems

An engine control system for a homogenous charge compression ignition (HCCI) engine includes an airflow determination module and a sensor diagnostic module. The airflow determination module generates a first plurality of estimates of airflow into the HCCI engine when the HCCI engine is operating in a first combustion mode, wherein the first plurality of estimates are based on an intake manifold absolute pressure (MAP), a mass air flow (MAF) rate, and a camshaft position. The sensor diagnostic module determines a state of at least one of a first plurality of sensors based on a predetermined threshold and differences between one of the first plurality of estimates and others of the first plurality of estimates, wherein the first plurality of sensors includes a MAP sensor, a MAF sensor, and a camshaft sensor.

FIELD

The present disclosure relates to homogenous charge compression ignition (HCCI) engine systems and more particularly to diagnostic systems and methods for sensors in HCCI engine systems.

BACKGROUND

Homogenous charge compression ignition (HCCI) engines combust an air/fuel (A/F) mixture within cylinders to produce drive torque. HCCI engines may combust the A/F mixture in different combustion modes. For example, in an HCCI combustion mode the A/F mixture may be automatically ignited when compressed by pistons (i.e. compression ignition). Alternatively, for example, in a spark ignition (SI) combustion mode the A/F mixture may be ignited by spark plugs in the cylinders after the pistons compress the A/F mixture.

HCCI combustion mode may improve engine efficiency and/or fuel economy compared to SI combustion mode. However, HCCI combustion mode may be limited to a predetermined HCCI operating zone in order to reduce combustion noise and protect the engine from damage due to excessive pressure increases associated with HCCI. Therefore, pressure sensors may be implemented in one or more of the cylinders and may be used to monitor cylinder pressure, particularly during HCCI combustion mode.

Furthermore, HCCI combustion mode may require precise A/F ratio control to prevent increased emissions. More specifically, lower peak temperatures during combustion (compared to SI combustion mode) may lead to incomplete burning of fuel. Therefore, carbon monoxide (CO) and/or hydrocarbon (HC) pre-catalyst emissions may be higher during HCCI combustion mode than in spark ignition combustion mode. For example, the increased CO and/or HC emissions may be higher during HCCI combustion mode due to incomplete oxidation and/or trapped crevice gases, respectively.

SUMMARY

An engine control system for a homogenous charge compression ignition (HCCI) engine includes an airflow determination module and a sensor diagnostic module. The airflow determination module generates a first plurality of estimates of airflow into the HCCI engine when the HCCI engine is operating in a first combustion mode, wherein the first plurality of estimates are based on an intake manifold absolute pressure (MAP), a mass air flow (MAF) rate, and a camshaft position. The sensor diagnostic module determines a state of at least one of a first plurality of sensors based on a predetermined threshold and differences between one of the first plurality of estimates and others of the first plurality of estimates, wherein the first plurality of sensors includes a MAP sensor, a MAF sensor, and a camshaft sensor.

A method for operating a homogenous charge compression ignition (HCCI) engine includes generating a first plurality of estimates of airflow into the HCCI engine when the HCCI engine is operating in a first combustion mode, wherein the first plurality of estimates are based on an intake manifold absolute pressure (MAP), a mass air flow (MAF) rate, and a camshaft position; and determining a state of at least one of a first plurality of sensors based on a predetermined threshold and differences between one of the first plurality of estimates and others of the first plurality of estimates, wherein the first plurality of sensors includes a MAP sensor, a MAF sensor, and a camshaft sensor.

DETAILED DESCRIPTION

HCCI engine systems may require precise A/F ratio control to prevent increased emissions during HCCI combustion mode. Thus, accurate measurement of airflow into the HCCI engine may be required to precisely control the airflow into and/or fuel supplied to the HCCI engine. The airflow into the HCCI engine may be estimated based on measurements from a plurality of different sensors. Therefore, each of the plurality of sensors may require diagnostics to determine whether the sensor is in a failure state and thus negatively affecting the accuracy of the airflow measurement.

For example, the plurality of sensors used to estimate airflow may include an intake manifold absolute pressure (MAP) sensor, a mass air flow (MAF) sensor, and a throttle position sensor (TPS). The MAP sensor may measure pressure inside the intake manifold. The MAF sensor may measure a rate of airflow into the intake manifold. The TPS may measure a relative position of the throttle (e.g., ranging from 0%, or closed, to 100%, or wide-open).

Typically, the MAP sensor, the MAF sensor, and the TPS sensor may be used collectively to determine whether one is in the failure state. For example only, differences may be determined between each of the airflow estimates and the differences may then be compared to predetermined thresholds to determine whether one of the sensors is in the failure state.

However, HCCI combustion mode requires commanding the throttle to an open position and controlling engine power output via fuel injection, similar to a diesel engine. Thus, the TPS sensor may not be used for diagnosing the failure state of one of the plurality of sensors when the HCCI engine is in HCCI combustion mode because the throttle position is static (i.e. not changing).

Therefore, systems and methods are presented that estimate airflow into an HCCI engine that is operating in HCCI combustion mode based on the MAP sensor, the MAF sensor, and a camshaft sensor. Thus, the systems and methods presented may diagnose a failure state of the MAP sensor, the MAF sensor, and/or the camshaft sensor during HCCI combustion mode. For example only, the systems and methods presented may diagnose a failure state of one of the plurality of sensors based on differences between each of the estimates and predetermined thresholds.

Furthermore, the systems and methods presented may estimate airflow into the HCCI engine when the HCCI engine is operating in SI combustion mode based on the MAP sensor, the MAF sensor, the camshaft sensor, and the TPS sensor. For example only, the systems and methods presented may diagnose a failure state of one of the sensors based on differences between each of the estimates and predetermined thresholds. In other words, incorporating an additional airflow estimate using the camshaft sensor may improve airflow estimation accuracy and/or sensor diagnostic accuracy (i.e. more estimations) compared to conventional diagnostic systems and methods.

Referring now toFIG. 1, an exemplary implementation of an HCCI engine system100is shown. The HCCI engine system100includes an HCCI engine102, an air inlet104, a throttle106, a TPS sensor108, a MAF sensor110, an intake manifold112, and an intake MAP sensor114.

Air is drawn into the HCCI engine102into the intake manifold112through the air inlet104that is regulated by the throttle106. The TPS sensor108may generate a TPS signal based on a relative position of the throttle106. The MAF sensor110may generate a MAF signal based on a mass air flow into the HCCI engine102. For example, an engine load may be determined based on the signal from the MAF sensor110. The MAP sensor114may generate a MAP signal based on a pressure inside the intake manifold112.

The HCCI engine system100further includes a fuel system116, a plurality of cylinders118, a camshaft120, an camshaft sensor122, an ignition system124, a plurality of spark plugs126, a plurality of cylinder pressure sensors128, a crankshaft130, and a crankshaft sensor132.

Air inside the intake manifold112may be distributed to the plurality of cylinders118. While four cylinders118are shown, it can be appreciated that the HCCI engine102may include other numbers of cylinders. The camshaft120actuates intake valves (not shown) that selectively open and close to enable the air from the intake manifold112to enter the cylinders118. While one camshaft120is show, it can be appreciated that more than one camshaft120may be implemented (e.g. dual overhead camshafts). The camshaft sensor122generates a camshaft phaser signal based on an angular position of the camshaft120. In other words, the camshaft phaser signal may correspond to a position of the intake and/or exhaust valves (not shown), and thus may be used to estimate airflow into the HCCI engine102.

The fuel system116may inject fuel into the intake manifold112at a central location (i.e central port injection, or CPI) or may inject fuel into the intake manifold112at multiple locations (i.e. multi-port injection, or MPI). Alternatively, the fuel system116may inject fuel directly into the cylinders118(i.e. direct fuel injection). The air mixes with the injected fuel to form the A/F mixture in the cylinders118. Cylinder pressure sensors128continuously measure pressure inside the cylinders118. For example only, the HCCI engine102may switch from HCCI combustion mode to Si combustion mode when pressure in one or more of the cylinders118is greater than a predetermined threshold.

Pistons (not shown) within the cylinders118compress the A/F mixture. At low-to-medium engine loads and low-to-medium engine speeds, the A/F mixture is automatically ignited when compressed (i.e. compression ignition). Here, the HCCI engine system100is operating in the HCCI combustion mode. Otherwise, the ignition system124may ignite the A/F mixture or provide spark assist during HCCI operation via the spark plugs126. Here, the HCCI engine system100is operating in the SI combustion mode. The combustion of the A/F mixture drives the pistons down, thereby rotatably driving the crankshaft130to produce the drive torque. The crankshaft sensor132may generate an engine speed signal based on a rotational speed (e.g. in revolutions per minute, or RPM) of the crankshaft130.

The HCCI engine system100further includes an exhaust manifold134, an exhaust outlet136, an exhaust back pressure (EBP) sensor138, an exhaust gas recirculation (EGR) line140, and an EGR valve142.

As previously mentioned, the camshaft120also actuates exhaust valves (not shown) that selectively open and close to enable combustion exhaust from the cylinders118to enter the exhaust manifold134. The exhaust gas may then be forced out of the engine system through the exhaust outlet136. The EBP sensor138may measure pressure of the exhaust gas in the exhaust manifold134.

The EGR line140and the EGR valve142may also introduce exhaust gas into the intake manifold112. More specifically, the EGR line140extends from the exhaust manifold134to the EGR valve142, and the EGR valve142may be mounted on the intake manifold112(as shown). Thus, the EGR valve142may selectively open and close to enable exhaust gas to enter the intake manifold112. For example, recirculation of exhaust gas may lower peak combustion temperatures, and thus may increase efficiency of the HCCI engine102.

The control module150controls operation of the HCCI engine system100based on driver input and various engine operating parameters. More specifically, the control module150may receive driver input from a driver input module160. For example only, the driver input module160may be an accelerator pedal and the driver input may correspond to a position (i.e. depression) of the accelerator pedal.

The control module150controls and communicates with the HCCI engine102, the throttle106(e.g. via electronic throttle control, or ETC), the fuel system116, the ignition system124, and the EGR valve140. The control module150also receives signals from the TPS sensor108, the MAF sensor110, the MAP sensor114, the camshaft phaser sensor122, the cylinder pressure sensors128, the crankshaft sensor132, and the EBP sensor138.

Referring now toFIG. 2, the control module150is shown in more detail. The control module150may include a combustion mode determination module200, a airflow determination module210, and a sensor diagnostic module220.

The combustion mode determination module200receives a plurality of signals corresponding to the combustion mode of the HCCI engine102. The combustion mode determination module200determines which combustion mode the engine system100is operating in based on the received signals. In other words, the combustion mode determination module200may determine whether the engine102is operating in SI combustion mode or HCCI combustion mode.

For example, the combustion mode determination module200may receive signals from the TPS sensor108, the spark plugs126, and the cylinder pressure sensors128. However, it can be appreciated that other status signals may be used in determining the combustion mode of the HCCI engine102. For example only, the combustion mode determination module200may determine that the HCCI engine102is operating in HCCI combustion mode when the TPS signal from the TPS sensor108does not change over a period of time (i.e. the throttle106is being held open). Alternatively, for example only, the combustion mode determination module200may determine that the HCCI engine102is operating in HCCI combustion mode when the spark plugs126are deactivated. Lastly, for example only, the combustion mode determination module200may determine that the HCCI engine102is operating in HCCI combustion mode when cylinder pressure from the cylinder pressure sensors128is less than a predetermined threshold.

The airflow determination module210receives the current combustion mode of the HCCI engine102. The airflow determination module210also receives signals from the TPS sensor108, the MAF sensor110, the MAP sensor114, and the camshaft sensor122. The airflow determination module210may generate airflow estimates based on each of the received signals and the combustion mode of the HCCI engine102.

More specifically, when the engine102is operating in SI combustion mode, the airflow determination module210generates an airflow estimate based on each of the TPS signal, the MAF signal, the MAP signal, and the camshaft signal.

However, when the engine102is operating in HCCI combustion mode, the airflow determination module210generate an airflow estimate based on each of the MAF signal, the MAP signal, and the camshaft signal. In other words, during HCCI combustion mode the throttle106is held open, and thus the TPS signal may not be used to estimate airflow.

The sensor diagnostic module220receives the airflow estimates corresponding to the MAF signal, the MAP signal, and the camshaft signal. The sensor diagnostic module220may also receive the airflow estimate corresponding to the TPS signal when the engine102is operating in HCCI combustion mode.

The sensor diagnostic module220determines a state of one of the TPS sensor108, the MAF sensor110, the MAP sensor114, and the camshaft phaser sensor122. More specifically, the sensor diagnostic module220compares the plurality of estimates to determine whether any of the plurality of sensors are in a failure state. For example, the sensor diagnostic module220may determine differences between each of the estimates, and then may compare the estimates to predetermined thresholds.

For example only, if differences between one of the signals and the other signals is greater than a predetermined threshold, the sensor diagnostic module220may determine that the sensor corresponding to the one of the signals is in the failure state. Therefore, when the sensor is in the failure state, the sensor may not be used when determining airflow into the HCCI engine102. Furthermore, an error signal (e.g. an error flag) may be generated corresponding to the failed sensor.

Referring now toFIG. 3, a method of operating the HCCI engine system100begins in step250. In step252, the control module150determines whether the HCCI engine102is operating in HCCI combustion mode or SI combustion mode. If the HCCI engine102is operating in HCCI combustion mode, control may proceed to step254. Otherwise, if the HCCI engine102is operating in SI combustion mode (i.e. default), control may proceed to step260.

In step254, the control module150generates airflow estimates based on signals from the MAF sensor110, the MAP sensor114, and the camshaft sensor122. In other words, the control module150may not generate an airflow estimate based on the TPS signal from the TPS sensor108.

In step256, the control module150may determine differences between each of the plurality of airflow estimates. In step258, the control module150may determine whether any of the plurality of sensors are in the failure state. For example, if one of the sensors is in the failure state the control module150may disregard the corresponding estimate when estimating airflow and/or may generate an error signal for the sensor. Control may then proceed to step266.

In step260, the control module150generates airflow estimates based on signals from the MAF sensor110, the MAP sensor114, the camshaft sensor122, and the TPS sensor108.

In step262, the control module150may determine differences between each of the plurality of airflow estimates. In step264, the control module150may determine whether any of the plurality of sensors are in the failure state. For example, if one of the sensors is in the failure state the control module150may disregard the corresponding estimate when estimating airflow and/or may generate an error signal for the sensor. Control may then proceed to step266.

In step266, the control module150controls combustion based on the airflow estimates. For example, the control module150may control an amount of fuel injected based on an average of the airflow estimates (i.e. the sensors not in the failure state). Control may then return to step252.