System and method of controlling combustion in an engine having an in-cylinder pressure sensor

A control system for an internal combustion engine comprises pressure sensing means, memory means, processing means, and fuel injection control means. Pressure sensing means generate in-cylinder pressure data used to calculate total heat generated during combustion cycle. Memory means store predetermined crank angle data, such as CA50 crank angle data, for variety of engine operating conditions. A CA50 crank angle is a crank angle position where fifty percent of total heat is generated. Memory means additionally stores allowable start of injection crank angle data. Processing means determine an observed CA50 crank angle. Processing means conducts comparison of at least one of the predetermined CA50 crank angle data against the observed CA50 crank angle to generate a start of fuel injection crank angle which impacts the observed CA50 crank angle during subsequent combustion cycle. Fuel injection control means controls start of fuel injection crank angle generated by the processing means.

TECHNICAL FIELD

The present disclosure relates to a system and method of controlling combustion within an internal combustion engine having an in-cylinder pressure sensor for monitoring combustion occurring within a cylinder, such that adjustments may be made to operating parameters of the internal combustion engine. The adjustments of the operating parameters allow combustion to function properly, i.e. without an usually high number of misfires, while allowing a very high rate of exhaust gas recirculation (“EGR”) to be used in combustion, and allowing fuel injection to begin after a cylinder has passed top dead center.

BACKGROUND

Many modern diesel engines have an exhaust system that features an exhaust gas recirculation (“EGR”) system that routes a portion of engine exhaust gas into an air intake system, such that a mixture of fresh air and engine exhaust is supplied to a combustion chamber during engine operation. In order to reduce certain pollutants found in exhaust gas of an internal combustion engine, such as NOx and particulate matter, several approaches have been tried, including using an after-treatment chemical in conjunction with a catalytic converter, a system often referred to as a selective catalyst reduction system or an “SCR system.” An SCR system adds complexity to an engine, and requires a catalyst that must be periodically replenished, which increases operating costs. If the catalyst is not replenished, the engine exhaust typically will not meet emissions standards, and the engine may be required to cease operations.

Therefore, a need exists for an engine capable of meeting emissions standards without the use of an after-treatment system to control parameters useful in reducing emissions of the engine.

SUMMARY

According to one embodiment, a control system for an internal combustion engine comprises pressure sensing means, memory means, processing means, and fuel injection control means. The pressure sensing means generate in-cylinder pressure data used to calculate the total heat generated during a combustion cycle. The memory means stores predetermined CA50 crank angle data for a variety of engine operating conditions. A CA50 crank angle is a crank angle position where fifty percent of the total heat during a combustion cycle is generated. The memory means additionally stores allowable start of injection crank angle data. The processing means determines an observed CA50 crank angle. The processing means conducts a comparison of at least one of the predetermined CA50 crank angle data against the observed CA50 crank angle to generate a start of fuel injection crank angle which impacts the observed CA50 crank angle during a subsequent combustion cycle. The fuel injection control means controls the start of fuel injection crank angle generated by the processing means.

According to one process, a method of controlling operation of an internal combustion engine is provided. An angular position of a crankshaft of the engine is monitored using a crank position sensor. A pressure reading is generated with a first in-cylinder pressure sensor for a first cylinder. An electronic control module is utilized to calculate the heat generated during the combustion cycle within the first cylinder based upon the pressure reading. An observed crank angle within the first cylinder is determined with the electronic control module based upon output of the crank position sensor and the first in-cylinder pressure sensor, wherein the observed crank angle is a crank angle position where a predetermined percent of the total heat is generated. The observed crank angle is compared against a predetermined crank angle stored in the electronic control module. A provisional start of injection crank angle is generated for the first cylinder in response to the comparison of the observed crank angle and the predetermined crank angle. A difference between the provisional start of injection crank angle of the first cylinder is compared to an average start of injection crank angle for a remainder of a plurality of cylinders to a preset phasing limit value. The fuel injector is utilized to match an actual start of fuel injection crank angle in the first cylinder to the provisional start of injection crank angle when the difference between the provisional start of injection crank angle and the average start of injection crank angle for the remainder of the plurality of cylinders is less than the preset phasing limit value.

According to another process, a method of controlling operation of an internal combustion engine is provided. An angular position of a crankshaft of the engine is monitored using a crank position sensor. A pressure reading is generated with a first in-cylinder pressure sensor for a first cylinder. An electronic control module is utilized to calculate the heat generated during the combustion cycle within the first cylinder based upon the pressure reading. An observed CA50 crank angle within the first cylinder is determined with the electronic control module based upon output of the crank position sensor and the first in-cylinder pressure sensor. The observed CA50 crank angle is compared against a predetermined CA50 crank angle stored in the electronic control module. A provisional start of injection crank angle is generated for the first cylinder in response to the comparison of the observed CA50 and the predetermined CA50. The provisional start of injection crank angle for the first cylinder is compared to a range of predetermined start of injection crank angles stored in the electronic control module. A difference between the provisional start of injection crank angle of the first cylinder is compared to an average start of injection crank angle for a remainder of a plurality of cylinders to a preset phasing limit value. The fuel injector is utilized to match an actual start of fuel injection crank angle in the first cylinder to the provisional start of injection crank angle when the provisional start of injection crank angle is within the range of predetermined start of injection crank angles, and when the difference between the provisional start of injection crank angle and the average start of injection crank angle for the remainder of the plurality of cylinders is less than the preset phasing limit value. An exhaust gas recirculation valve position is generated for the first cylinder when one of the difference between the provisional start of injection crank angle for the first cylinder and the average start of injection crank angle for the remainder of the plurality of cylinders exceeds the preset phasing limit and the provisional start of injection crank angle is outside of the range of predetermined start of injection crank angles. The fuel injector is utilized to match an actual start of fuel injection crank angle into the first cylinder to an adjusted start of injection crank angle when one of the difference between the provisional start of injection crank angle for the first cylinder and the average start of injection crank angle for the remainder of the plurality of cylinders exceeds the preset phasing limit, and the provisional start of injection crank angle is outside of the range of predetermined start of injection crank angles. A position of the exhaust gas recirculation valve is adjusted to the generated exhaust gas recirculation valve position.

DETAILED DESCRIPTION

FIG. 1shows an engine10having an exhaust system12. The exhaust system12has an exhaust gas recirculation (“EGR”) portion13. The EGR portion13has an EGR cooler14and an EGR valve16. The EGR cooler14reduces the temperature of exhaust gas within the EGR portion13. The exhaust system12additionally is shown as having a first turbocharger turbine18and a second turbocharger turbine20. The EGR valve16controls the flow of exhaust gas within the EGR portion13.

The engine10additionally has an air intake system22. The air intake system22has a first turbocharger compressor24and a second turbocharger compressor26. A charge air cooler28is additionally provided to cool intake air within the air intake system22. A first throttle valve30and a second throttle valve32are also disposed within the air intake system22. The first turbocharger turbine18and the first turbocharger compressor24form a first turbocharger and the second turbocharger turbine20and the second turbocharger compressor26form a second turbocharger. It is contemplated that the first turbocharger and the second turbocharger may be variable geometry turbochargers.

Turning now toFIG. 2, a cross section of a cylinder34of the engine10. The cylinder34has a piston36that moves reciprocally within the cylinder34. A cylinder head38is disposed above the cylinder34, such that the movement of the piston36within the cylinder34increases a pressure within the cylinder34. An in-cylinder pressure sensor40is additionally provided. The in-cylinder pressure sensor40is disposed within the cylinder head38and a portion of the in-cylinder pressure sensor40is exposed within the cylinder34. The in-cylinder pressure sensor40monitors the pressure within the cylinder34. In a multi-cylinder engine10, there are multiple sensors40forming a sensor group41.

FIG. 3depicts a block diagram for a control system42for the engine10, whileFIGS. 6aand 6bdepict a flow chart of a method of controlling the engine10. The control system42has a fuel system control component44and an air system control component46. The fuel system control component44has an accelerator position sensor48and an engine speed sensor50. The accelerator position sensor48and the engine speed sensor50are in electrical communication with a fuel system controller52. The fuel system controller52has a memory that stores fuel injection quantity data54as well as fuel injection timing data56, wherein both data54,56are graphically represented with curves. Based upon the input received from the accelerator position sensor48and the engine speed sensor50, the fuel system controller52retrieves a fuel injection quantity output from the fuel injection quantity data54(block602,FIG. 6a) and also retrieves a fuel injection timing output from the fuel injection timing data56(block610,FIG. 6a). The fuel injection quantity output is communicated to a fuel injection quantity comparator58, while the fuel injection timing output is communicated to a fuel injection timing comparator60.

The fuel system control component44additionally utilizes the group41of in-cylinder pressure sensors40that communicate with a combustion monitoring processor64that contains a fuel system memory66containing fuel injection timing correction data (block612,FIG. 6a) and fuel injection quantity correction data (block604,FIG. 6a) based upon the output of the group41of in-cylinder pressure sensors40. Outputs of the fuel system memory66is electronically communicated to the fuel injection quantity comparator58and the fuel injection timing comparator60(block614,FIG. 6a). The fuel injection quantity comparator58compares the output of the fuel injection quantity data54with the output from the fuel system memory66of the combustion monitoring processor64(block606,FIG. 6a) to generate a corrected fuel injection quantity communicated to a fuel injector70(blocks608,610,FIG. 6a). Similarly, the fuel injection timing comparator60compares the output of the fuel injection timing data56with the output from the fuel system memory66of the combustion monitoring processor64(block614,FIG. 6a) to generate a corrected fuel injection timing communicated to a fuel injector70(blocks616,618,FIG. 6a).

The air system control component44of the control system42for the engine10additionally utilizes the group41of in-cylinder pressure sensors40that communicate with the combustion monitoring processor64that has an air intake system memory68(blocks620,630,FIG. 6b). An air intake system controller72has a memory that stores turbocharger data74as well as EGR system data76. The air intake system controller72retrieves a turbocharger setting from the turbocharger data74based upon engine operating conditions (block622,FIG. 6b). The air intake system controller72additionally retrieves an EGR valve setting from the EGR system data76(block632,FIG. 6b). Output of the turbocharger data74and the air intake system memory68is transmitted to a turbocharger comparator78which compares the turbocharger data74with the output of the air intake system memory68(block624,FIG. 6b) and may adjust the turbocharger setting output using the turbocharger data74(block626,FIG. 6b) to generate a corrected turbocharger setting to a turbocharger82(block628,FIG. 6b).

The EGR system data76from the air intake system controller72is transmitted to an EGR system comparator80where the EGR system comparator80compares it to the output of the air intake system memory68(block634,FIG. 6b) and may adjust the EGR setting output using the EGR system data76(block636,FIG. 6b) to generate a corrected EGR system setting to an EGR valve84(block638,FIG. 6b).

Turning now toFIG. 4, a control system86is shown having a processor88, an interface90, and an ECM92. The processor88is disposed in electrical communication with both the interface90and the ECM92. The processor88is additionally disposed in electrical communications with an in-cylinder pressure sensor40, a cam position sensor96and a crank position sensor98. The processor88utilizes the input from the in-cylinder pressure sensor40, the cam position sensor96, and the crank position sensor98to generate a CA50 crank angle using a CA50 estimator100of the processor88.

The CA50 crank angle is the crank angle where 50% of the heat is generated for a particular combustion cycle. In order to determine when 50% of the heat has been generated, the in-cylinder pressure sensor40is utilized to determine a total heat release for the combustion of fuel within the cylinder34based upon the pressure within the cylinder34. The output of the in-cylinder pressure sensor40may also be utilized by a torque estimator102of the processor88.

While the CA50 crank angle is described in this disclosure, it is contemplated that a different crank angle may be utilized that corresponds to a specific percentage of heat generated for a particular combustion cycle, and the invention is not limited to the specific crank angles or specific percentages heat generated. For instance, it is additionally contemplated that a range of a CA10 crank angle to a CA90 crank angle may be utilized, wherein the CA10 crank angle is the crank angle where 10% of the heat is generated for a particular combustion cycle, and CA90 is the crank angle where 90% of the heat is generated for a particular combustion cycle. Therefore, it is contemplated that CA50 may be substituted by a crank angle (CA) corresponding to another predetermined percentage amount of heat generated during combustion without altering the principals of this disclosure.

The in-cylinder pressure sensor40is utilized to determine the pressure within the cylinder from combustion by comparing the actual pressure within the cylinder, to the pressure that would be within the cylinder without any combustion occurring. This is done by comparing the output of the in-cylinder pressure sensor40at a crank angle after a piston within the cylinder has passed top dead center (“TDC”) with the output of the in-cylinder pressure sensor40at a corresponding crank angle before the position within the cylinder has reached TDC. For example, the output of the in-cylinder pressure sensor40at a crank angle 25 degrees after TDC is compared to the output of the in-cylinder pressure sensor40at a crank angle 25 degrees before TDC, wherein the pressure difference is based upon combustion of fuel within the cylinder34. The pressure within the cylinder34attributed to combustion from the in-cylinder pressure sensor40may be used to generate a heat release amount, such that a crank angle may be determined where various percentages of the total amount of heat released from a particular fuel injection into a particular cylinder may be calculated. Thus, the CA50 estimator100may calculate a CA50 crank angle that corresponds to the crank angle where 50% of the heat released during combustion of a particular combustion cycle within a particular cylinder occurs.

Similarly, the torque estimator102may utilize the output of the in-cylinder pressure sensor40to calculate a torque output of the engine10. The torque estimator102utilizes the output of the in-cylinder pressure sensor40and a known equation of the relationship between pressure within the cylinder34and the geometry the engine10to calculate an estimate of torque produced by the engine10. The torque can be calculated by the following formula: Torque=BMEP*V/4Π, where BMEP is the brake mean effective pressure and V is the volume of the piston. BMEP may be calculated using the formula BMEP=IMEP−FMEP, where IMEP is the indicated mean effective pressure and FMEP is the friction mean effective pressure. IMEP may be generated from the output of the in-cylinder pressure sensor40when fuel in injected into a cylinder34, and FMEP may be calculated using the in-cylinder pressure sensor40when no fuel is injected into a cylinder34during a cycle, or may be estimated.

The processor88still further has a misfire prevention module104adapted to monitor combustion characteristics within the engine10. The misfire prevention module104is adapted to compare an output of the CA50 estimator100with an output from the ECM92that contains a target CA50 value retrieved from a memory of the ECM92. The misfire prevention module104will generate an output signal to adjust at least one of fuel injection timing, EGR valve position, VGT settings, and variable valve timing settings to adjust the actual CA50 value calculated by the CA50 estimator100to match the target CA50 value stored in a memory of the ECM92as will be explained in further detail below.

The interface90of the control system86allows for control of parameters used for the misfire prevention module104of the processor88. The interface90allows limits for the adjustments of the fuel injection timing, and airflow to the engine10to be corrected. The interface90additionally allows in-cylinder pressure sensor40feedback to be turned on and off, depending on expected operating conditions of the engine10.

FIG. 5shows a schematic of a control system106for a diesel engine. The control system106is adapted to control combustion phasing, that is the crank angle where CA50 occurs in cylinders within the engine. Combustion phasing may also be controlled between cylinders of a multi-cylinder engine, such that CA50 crank angle for a first cylinder is within a predefined number of degrees from the CA50 crank angle for a second cylinder. Using both a model based portion108and an empirical portion110of the control system106, combustion within the engine is controlled.

The model based portion108has a memory that contains an air flow estimate112based upon observed operating conditions of the engine10, such as torque output, and engine speed. The output of the air flow estimate112is transmitted to an air flow comparator114. As explained below, the air flow comparator114also receives an input based upon air flow estimated by the in-cylinder pressure sensor40. The output of the air flow comparator114is transmitted to a throttle controller116and an EGR controller118. The throttle controller116receives input from an engine speed and torque monitor120, while the EGR controller118further receives input from an engine speed and torque monitor120.

Output from the EGR controller118is transmitted to an EGR emission limiter124, to ensure that the EGR setting is sufficient to allow the engine to meet emission standards. Output of the throttle controller116is transmitted to an intake air comparator126where it is compared to a predetermined intake air setting128. Output of the intake air comparator126is transmitted to an intake manifold air estimator134.

Similarly, output from the EGR emission limiter124is transmitted to an EGR comparator130where it is compared to a predetermined EGR setting132. Output of the EGR comparator130is also transmitted to the intake manifold air estimator134. Output from the intake manifold air estimator134is transmitted to a fuel injector controller136, and EGR valve controller138, and a variable geometry turbocharger (VGT) controller140, to be used in helping to control fuel injection timing, the amount of EGR delivered to the engine, and the VGT setting.

The intake manifold air estimator134also communicates with an in-cylinder pressure sensor based air estimator142. The in-cylinder pressure sensor based air estimator142also receives input from an in-cylinder pressure sensor40, an intake manifold pressure sensor146, and an EGR rate estimator148. The in-cylinder pressure sensor based air estimator142generates an output that is communicated with the airflow comparator114, so that the airflow comparator114may calculate a correction to the air flow estimate112stored in the memory. The correction of the airflow estimate112allows for better control of the air/fuel ratio of the engine.

Turning now to the empirical portion110of the control system106, as well as the flow chart shown inFIGS. 7aand 7b, input from the in-cylinder pressure sensor40, a calculated CA50 value150(block702,FIG. 7a), and a calculated torque152are transmitted to a feedback controller154. The feedback controller154compares the calculated CA50 value150with a stored CA50 value based on observed engine operating conditions (block704,FIG. 7a) and may adjust the turbocharger setting output using the turbocharger setting data74(block706,FIG. 7a). If the calculated CA50 value150generally corresponds to the stored CA50 value, very few adjustments, or even no adjustments, are made to operating parameters. However, if the calculated CA50 value150does not correspond to the stored CA50 value, the feedback controller154generates a provisional start of injection crank angle (block708,FIG. 7a), and compares the provisional start of injection crank angle to a start of injection adjustment limit stored in a memory of the feedback controller154(block710,FIG. 7a). If the provisional start of injection crank angle is within the start of injection adjustment limit, the start of injection crank angle is adjusted (block712,FIG. 7a). If the provisional start of injection crank angle is not within the start of injection adjustment limit, the feedback controller154generates a provisional EGR valve adjustment (block716,FIG. 7a), and sets the start of injection crank angle at the adjustment limit (block714,FIG. 7a).

The provisional EGR valve adjustment is also compared to an EGR valve adjustment limit (block718,FIG. 7a). If the provisional EGR valve adjustment is within the EGR valve adjustment limit, the EGR valve is set to the provisional EGR valve adjustment position (block720,FIG. 7b). However, if the provisional EGR valve adjustment is outside of the EGR valve adjustment limit, the feedback controller154generates a VGT position setting (block724,FIG. 7b), and sets the EGR valve adjustment position at the adjustment limit (block722,FIG. 7b). The VGT position is set at the generated VGT position setting (block726,FIG. 7b).

The feedback controller154communicates with an instability predictor156. The instability predictor156is used by an engine having a plurality of cylinders to compare the corrections required by one cylinder to settings for the remaining cylinders. If the instability predictor156detects that the setting for the start of injection crank angle for a first cylinder is outside of a range from an average start of injection crank angle for all of the cylinders of the engine, the instability predictor156will set an adjusted start of injection crank angle, and will adjust at least one of the EGR valve adjustment and the VGT position setting to compensate for the adjusted start of injection crank angle. The instability predictor156therefore generates a final start of injection crank angle158, a final EGR valve adjustment position160, and a final VGT position setting162. The final start of injection crank angle158is transmitted to the fuel injector controller136, the final EGR valve adjustment position160is transmitted to the EGR valve controller138, and the final VGT position setting162is transmitted to the VGT controller140.

It is additionally contemplated that an intake throttle position setting and a variable valve actuation setting may also be generated as described above with respect to the EGR valve position and the VGT position setting. It is contemplated that the control system106may be executed by an ECM, or that separate controllers may be utilized that simply communicate with each other.

The present disclosure is adapted to allow an engine to operate with high levels of EGR, i.e. above 35%, and with a start of fuel injection occurring after a piston within a cylinder has passed top dead center. These aspects of this disclosure allow combustion to remain stable, even with fuel injection starting after the piston has passed top dead center. Fuel injection occurring after the piston has passed top dead center while utilizing EGR rates above 35% have been found to reduce engine emissions of NOx and particulate matter significantly. However, combustion tends to become unstable with increasing amounts of EGR as less oxygen is present within EGR for use in combustion. Additionally, initiating fuel injection after TDC may lead to unstable combustion as mixing of fuel with air within the cylinder may not sufficiently atomize the fuel for stable combustion to occur, thus, combustion under such conditions must be carefully monitored and controlled.

As described above, the present disclosure may be applied on a per-cylinder basis, such that fuel injection timing, and EGR valve position setting are adjusted to ensure proper combustion within a single cylinder, or operations of a plurality of cylinders may be controlled by an instability predictor to ensure that proper combustion phasing is maintained between the plurality of cylinders.