METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE EMPLOYING A DEDICATED-CYLINDER EGR SYSTEM

Abstract

A multi-cylinder spark-ignition internal combustion engine includes a plurality of first and second intake valves disposed between the air intake system and a corresponding plurality of engine cylinders. The engine also includes a dedicated-cylinder exhaust gas recirculation (EGR) system including an exhaust runner fluidly connected between exhaust valve(s) of one of the cylinders and the air intake system of the engine. A controllable intake valve activation system is configured to control openings of the plurality of first and second intake valves. A controller is operatively connected to the engine and the controllable intake valve activation system, and includes an instruction set to monitor operation of the engine, and control openings of the plurality of first intake valves and control openings of the plurality of second intake valves to generate in-cylinder mixing of a cylinder charge that achieves combustion stability for an engine speed/load operating point.

Description

INTRODUCTION

Internal combustion engines (engines) produce mechanical power in the form of torque and rotational speed by combusting a mixture of air and fuel within one or more combustion chambers. During combustion, various exhaust gases are produced. A portion of the exhaust gas can be recirculated back into the engine cylinders, e.g., via an exhaust gas recirculation system. The recirculated exhaust gas can displace an amount of combustible mixture in the cylinder resulting in increased engine efficiency and lower combustion temperatures, which may serve to reduce formation of certain gaseous byproducts.

SUMMARY

A multi-cylinder spark-ignition internal combustion engine system (engine) is described, and includes an engine subassembly including an engine block defining a plurality of cylinders and a plurality of first and second intake valves disposed in a cylinder head between an air intake system and the cylinders. The engine also includes a dedicated-cylinder exhaust gas recirculation (EGR) system including an exhaust runner fluidly connected between exhaust valve(s) of one of the cylinders and the air intake system of the engine. A controllable intake valve activation system is configured to control openings of the plurality of first and second intake valves. A controller is operatively connected to the engine and the controllable intake valve activation system, and includes an instruction set that is executable to monitor operation of the engine, and control openings of the plurality of first intake valves and control openings of the plurality of second intake valves to generate in-cylinder mixing of a cylinder charge that achieves combustion stability for an engine speed/load operating point.

One aspect includes monitoring operation of the engine to determine an engine speed/load operating point and operate the intake valve activation system to control openings of the first intake valves and the second intake valves based upon the engine speed/load operating point.

One aspect includes operating the intake valve activation system to open both the first intake valve and the second intake valve during each intake stroke of each combustion cycle.

One aspect includes operating the intake valve activation system to open only the first intake valve or only the second intake valve during each intake stroke of each combustion cycle.

One aspect includes operating the intake valve activation system to open only the first intake valve or only the second intake valve during each intake stroke of each combustion cycle, wherein open time of the first intake valve or the second intake valve is either increased or reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an internal combustion engine including an engine subassembly, an air intake system, an exhaust system, a dedicated-cylinder exhaust gas recirculation (EGR) system and a turbocharger, in accordance with the disclosure; and

FIGS. 2-1 through 2-6 graphically show first through sixth profiles, respectively, that may be employed to control an embodiment of the internal combustion engine described with reference to FIG. 1, wherein each of the profiles is in the form of a valve opening timing chart including timing and lift for first and second intake valves and exhaust valves in relation to crankshaft position for a single cylinder over a single four-stroke engine cycle, in accordance with the disclosure.

DETAILED DESCRIPTION

The components of the disclosed embodiments, as described and illustrated herein, may be arranged and designed in a variety of different configurations. Thus, the following detailed description is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible embodiments thereof. In addition, while numerous specific details are set forth in the following description in order to provide a thorough understanding of the embodiments disclosed herein, some embodiments can be practiced without some or all of these details. Moreover, for the purpose of clarity, certain technical material that is known in the related art has not been described in detail in order to avoid unnecessarily obscuring the disclosure. Furthermore, the drawings are in simplified form and are not to precise scale. Any use of directional terms may not be construed to limit the scope of the disclosure in any manner. Furthermore, the disclosure, as illustrated and described herein, may be practiced in the absence of any element which is not specifically disclosed herein. Furthermore, the teachings may be described herein in terms of functional and/or logical block components and/or various processing steps. It should be realized that such block components may be composed of any number of hardware, software, and/or firmware components configured to perform the specified functions. As employed herein, the term “upstream” and related terms refer to elements that are towards an origination of a flow stream relative to an indicated location, and the term “downstream” and related terms refer to elements that are away from an origination of a flow stream relative to an indicated location.

Referring now to the drawings, wherein the depictions are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIG. 1 schematically illustrates a four-cycle internal combustion engine assembly (engine) 10 including an engine subassembly 12, an air intake system 14, an exhaust system 16 and a dedicated-cylinder exhaust gas recirculation (EGR) system 60. In one embodiment and as shown, a turbocharger 18 may be employed. In one embodiment, an engine-driven or electric motor-driven supercharger may be employed. The engine 10 may be deployed on a vehicle to provide propulsion power, wherein the vehicle may include, but not be limited to a mobile platform in the form of a commercial vehicle, industrial vehicle, agricultural vehicle, passenger vehicle, aircraft, watercraft, train, all-terrain vehicle, personal movement apparatus, robot and the like to accomplish the purposes of this disclosure.

The engine 10 is preferably configured as a high-compression-ratio spark-ignited internal combustion engine, and may also include another suitable internal combustion engine that combusts hydrocarbon fuels to generate torque. The engine subassembly 12 preferably includes an engine block defining a plurality of cylinders 20 (referenced as cylinders 1-4), a corresponding plurality of pistons that reciprocate within the cylinders 20, a rotatable crankshaft that couples to the pistons, a cylinder head 21, and other engine components such as piston connecting rods, pins, bearings and the like. Each of the cylinders 20 with corresponding piston and portion of the cylinder head 21 defines a variable-volume combustion chamber 15. Each of the plurality of cylinders 20 selectively fluidly communicates with the air intake system 14 via first and second intake valves 23, 24, respectively, to receive fresh/oxygenated air, and each of the plurality of cylinders 20 selectively fluidly communicates with the exhaust system 16 via exhaust valves 25 to expel the byproducts of combustion. While the illustrated engine 10 depicts an inline 4-cylinder (I4) engine, the present technology is equally applicable to other engine configurations, including, by way of non-limiting examples, I2, I3, I5 and I6 engines, or V-2, V-4, V-6, V-8, V-10, and V-12 engines, among others.

The cylinder head 21 includes a plurality of intake ports and associated first and second intake valves 23, 24, respectively, for each of the cylinders 20, a plurality of exhaust ports and associated exhaust valves 25 for each of the cylinders 20, and other ports and associated components including fuel injectors, spark igniters and combustion sensors. The plurality of first and second intake valves 23, 24 are disposed between the air intake system 14 and a corresponding one of the cylinders 20. The plurality of exhaust valves 25 are disposed between a corresponding one of the cylinders 20 and the exhaust system 16. The exhaust system 16 preferably includes a first exhaust manifold 36 and a second exhaust manifold 62 that are disposed to entrain and direct exhaust gases that are expelled from the engine 10 via openings of the exhaust valves 25.

The first and second intake valves 23, 24 operatively connect to a variable intake valve activation system 22 that preferably includes a rotatable camshaft whose rotation is indexed to rotation of the crankshaft. The exhaust valves 25 operatively connect to an exhaust valve activation system 26 that preferably includes a rotatable camshaft whose rotation is indexed to rotation of the crankshaft. In one embodiment, the exhaust valve activation system 26 may be variably controlled, as described herein.

The air intake system 14 can generally include one or more of, a fresh-air inlet, an exhaust gas recirculation (EGR) mixer 27, a charge air cooler 28, a throttle 30 and an intake manifold 32. During operation of the engine 10, fresh air or intake air 34 can be ingested by the air intake system 14 from the atmosphere through an associated air-cleaner assembly via the fresh-air inlet. The throttle 30 can include a controllable baffle that is configured to regulate the total flow of air through the air intake system 14, and ultimately into the cylinders 20 via the intake manifold 32. Airflow from the intake manifold 32 into each of the cylinders 20 is controlled by the first and second intake valves 23, 24, the activation of which is controlled by the variable intake valve activation system 22. Exhaust flow out of each of the cylinders 20 to the first and second exhaust manifolds 36, 62 is controlled by the exhaust valve(s) 25, the activation of which may be controlled by the exhaust valve activation system 26.

The term “dedicated-cylinder EGR system” as employed herein refers to a system in which all exhaust gases generated in one or a plurality of the cylinders 20 are separated and routed to the air intake system 14. In one embodiment, the dedicated-cylinder EGR system 60 includes the second exhaust manifold 62, a controllable diverter valve 64, and an in-stream EGR heat exchanger 65 that fluidly connects to the air intake system 14 at an EGR mixer 27 that is located upstream of the charge air cooler 28 and the throttle 30. The second exhaust manifold 62 entrains exhaust gas flow from cylinder 4 in this embodiment, and channels such flow to the air intake system 14 when the diverter valve 64 is controlled to a first position. The second exhaust manifold 62 entrains and channels exhaust gas flow from cylinder 4 to the exhaust system 16 via a second conduit 70 when the diverter valve 64 is controlled to a second position. Other elements preferably include the in-stream EGR heat exchanger 65 that is configured to reduce or otherwise manage temperature of the recirculated exhaust gas 41, a first temperature sensor 61 that is disposed to monitor temperature of the recirculated exhaust gas 41 upstream of the in-stream EGR heat exchanger 65 and a second temperature sensor 63 that is disposed to monitor temperature of the recirculated exhaust gas 41 downstream of the in-stream EGR heat exchanger 65. Thus, the dedicated-cylinder EGR system 60 fluidly communicates with the air intake system 14 to route the recirculated exhaust gas 41 to the air intake system 14. This recirculated exhaust gas 41 can mix with the fresh air 34 within the EGR mixer 27 to dilute the oxygen content of the intake air charge. In one embodiment of the engine 10 employing the dedicated-cylinder EGR system 60, the magnitude of EGR dilution of the intake air charge is approximately a ratio of the number of dedicated EGR cylinders to the total number of cylinders. In FIG. 1, one cylinder, i.e., cylinder 4 supplies dedicated EGR for engine 12 that has a total of 4 cylinders so EGR dilution is approximately 25%. The use of the dedicated-cylinder EGR system 60 can increase fuel efficiency in spark ignition engines. Furthermore, the dedicated-cylinder EGR system 60 can reduce the combustion temperature and emission production from the engine 10. The first exhaust gas 40 is produced by the remaining three cylinders 20 (i.e., cylinders 1-3) and is expelled from the engine 10 via the exhaust system 16 through the aftertreatment device 42.

The variable intake valve activation system 22 includes mechanisms and control routines that interact with the intake camshaft(s) to control the openings and closings of the first and second intake valves 23, 24, including selectively deactivating one or both of the first and second intake valves 23, 24. One mechanization that may be configured to individually selectively deactivate one or both the first and second intake valves 23, 24 includes stationary hydraulic lash adjusters (SHLA) and roller finger followers (RFF). Another mechanization that may be configured to individually selectively deactivate one or both the first and second intake valves 23, 24 includes an intake camshaft and related componentry that includes a sliding cam having multiple cam lobes that may be selectively disposed to interact with and control openings and closings of one or both of the first and second intake valves 23, 24. SHLAs, RFFs and sliding cam mechanizations are known to those skilled in the art.

Controlling the variable intake valve activation system 22 to control openings and closings of the first and second intake valves 23, 24 includes opening both the first intake valve 23 and the second intake valve 24 during the intake stroke of the combustion cycle for each of the cylinders 20 under certain operating conditions. This further includes controlling the variable intake valve activation system 22 to selectively deactivate one of the first and second intake valves 23, 24 such that the deactivated valve does not open during the intake stroke of the combustion cycle for each of the cylinders 20. This may include controlling the variable intake valve activation system 22 to activate only the first intake valve 23 while deactivating the second intake valve 24 for each of the cylinders 20 such that the deactivated second intake valve 24 does not open during the intake stroke of the combustion cycle for each of the cylinders 20 under certain operating conditions. This may include controlling the variable intake valve activation system 22 to deactivate only the first intake valve 23 while activating the second intake valve 24 for each of the cylinders 20 under certain operating conditions such that the deactivated first intake valve 23 does not open during the intake stroke of the combustion cycle for each of the cylinders 20 under certain operating conditions. Such operations are described with reference to FIGS. 2-1 through 2-6.

In one embodiment, the exhaust valve activation system 26 may include a variable camshaft phaser (VCP)/variable lift control (VLC) device that interacts with the exhaust camshaft(s) to control the openings and closings of the exhaust valves 25. Controlling the openings and closings of the first and second intake valves 23, 24 and the exhaust valves 25 can include controlling magnitude of valve lift and/or controlling phasing, duration or timing of valve openings and closings. The exhaust valve activation system 26 including the VCP/VLC device is disposed to control interactions between the exhaust valves 25 and an exhaust camshaft in one embodiment. Alternatively, the exhaust valves 25 interact directly or via followers with an exhaust camshaft. The rotations of the intake and exhaust camshafts are linked to and indexed, variably in the case of VCP application, to rotation of the engine crankshaft, thus linking openings and closings of the intake and exhaust valves 23 and 25 to positions of the crankshaft and the pistons housed in the cylinders 20.

Reciprocating movement of each of the pistons in its corresponding cylinder is between a piston bottom-dead-center (BDC) location and a piston top-dead-center (TDC) location in concert with rotation of the crankshaft. Engines operating with a four-stroke engine cycle sequentially execute a repeated pattern of intake, compression, power and exhaust strokes. During the compression stroke, a fuel/air charge in the combustion chamber 15 is compressed by rotation of the crankshaft and movement of the piston in preparation for ignition. The intake valve 23 and the exhaust valve 25 are closed during at least a portion of the compression stroke. Closing of the intake valve 23 can be controlled by controlling the variable intake valve activation system 22, resulting in controlling an effective compression ratio. The effective compression ratio is defined as a ratio of a volumetric displacement of the combustion chamber 15 at closing of the intake valve 23 and a minimum volumetric displacement of the combustion chamber 15, e.g., when the piston is at TDC. The effective compression ratio may differ from a geometric compression ratio, which is defined as a ratio of a maximum volumetric displacement of the combustion chamber 15 occurring at BDC and the minimum volumetric displacement of the combustion chamber 15 occurring at TDC without regard to closing time of the intake valve 23. An early or delayed closing of the intake valve 23 may trap less air in the combustion chamber 15, thus decreasing pressure and therefore decreasing temperature in the combustion chamber 15 during combustion. In one embodiment, fuel is metered and injected into the combustion chamber 15 during the intake stroke. One fuel injection event may be executed to inject fuel; however, multiple fuel injection events may be executed. In one embodiment, fuel is injected early enough in the intake stroke to allow adequate premixing of the fuel/air charge in the combustion chamber 15.

Referring again to FIG. 1, the charge air cooler 28 can be disposed between the EGR mixer 27 and the throttle 30. In general, the charge air cooler 28 can be a radiator-style heat exchanger that uses a flow of atmospheric air or liquid coolant to cool an intake air charge that is a mixture of fresh air and recirculated exhaust gas. As may be appreciated, the intake air charge can be warmer than atmospheric temperature due to the pressurization via the compressor 52, in conjunction with the mixing of the higher temperature recirculated exhaust gas 41. The charge air cooler 28 can cool the gas mixture to increase its density/volumetric efficiency, while also reducing the potential for abnormal combustion such as pre-ignition or knock.

The exhaust gas passes through an aftertreatment device 42 to catalyze, reduce and/or remove exhaust gas constituents prior to exiting the exhaust system 16 via a tailpipe 44. The aftertreatment device 42 can include one or combinations of catalytic devices, including, e.g., a three-way catalytic device, an oxidation catalyst, a hydrocarbon trap, a NOx adsorber, or any other suitable components and accompanying pipes and valves that function to oxidize, reduce, and otherwise catalyze and/or remove various exhaust gas constituents prior to exiting the exhaust system 16.

The air intake system 14 and the exhaust system 16 can be in mechanical communication through the turbocharger 18. The turbocharger 18 is in fluid communication with the exhaust system 16 and the turbocharger 18 expels the first exhaust product 40. The turbocharger 18 can include a turbine 50 in fluid communication with the exhaust system 16 and a compressor 52 in fluid communication with the air intake system 14. The turbine 50 and the compressor 52 can be mechanically coupled via a rotatable shaft 54. The turbocharger 18 can utilize the energy of the first exhaust product 40 flowing from the engine 10 to spin the turbine 50 and the compressor 52. The rotation of the compressor 52 draws fresh air 34 in from the fresh air inlet and compresses the air 34 into the remainder of the air intake system 14. The first exhaust product 40 is expelled through the turbocharger 18. Once the first exhaust product 40 is expelled from the turbocharger 18, the first exhaust product 40 flows toward the aftertreatment device 42.

Operation of the engine 10 can be monitored by a plurality of sensing devices. By way of non-limiting examples, the sensing devices may include a combustion sensor 17 that is disposed to monitor an engine parameter that is associated with combustion in each cylinder, a first exhaust gas sensor 37 that is disposed in the first exhaust manifold 36, a second exhaust gas sensor 43 that is disposed in the exhaust gas feedstream downstream of the aftertreatment device 42, a temperature sensor 78 that is disposed to monitor temperature of the aftertreatment device 42, the first temperature sensor 61 that is disposed to monitor temperature of recirculated exhaust gas upstream of the in-stream EGR heat exchanger 65 and the second temperature sensor 63 that is disposed to monitor temperature of recirculated exhaust gas downstream of the in-stream EGR heat exchanger 65.

The combustion sensor 17 may be disposed to monitor an engine parameter associated with combustion in each cylinder, and may be in the form of an in-cylinder pressure sensor in one embodiment. Alternatively, the combustion sensor 17 may be in the form of a rotational speed sensor that is disposed to monitor rotational speed and position of the crankshaft, with accompanying algorithms to evaluate crankshaft speed variations, or another suitable combustion monitoring sensor. The aforementioned sensors are provided for purposes of illustration. Any one of or all of the aforementioned sensors may be replaced by other sensing devices that monitor a parameter associated with operation of the engine 10, or may instead be replaced by an executable model to derive a state of an engine operating parameter.

A controller 72 can be part of an electronic control module that is in communication with various components of the vehicle. The controller 72 includes a processor 74 and a memory 76 on which is recorded instructions for communicating with the diverter valve 64, the variable intake valve activation system 22, the turbocharger 18, the aftertreatment device 42, etc. The controller 72 is configured to execute the instructions from the memory 76, via the processor 74. For example, the controller 72 can be a host machine or distributed system, e.g., a computer such as a digital computer or microcomputer, acting as a vehicle control module, and/or as a proportional-integral-derivative (PID) controller device having a processor, and, as the memory 76, tangible, non-transitory computer-readable memory such as read-only memory (ROM) or flash memory. The controller 72 can also have random access memory (RAM), electrically erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and any required input/output circuitry and associated devices, as well as any required signal conditioning and/or signal buffering circuitry. Therefore, the controller 72 can include all software, hardware, memory 76, algorithms, calibrations, connections, sensors, etc., necessary to monitor and control the diverter valve 64, the variable intake valve activation system 22, the turbocharger 18, the aftertreatment device 42, etc. As such, a control method can be embodied as software or firmware associated with the controller 72. It is to be appreciated that the controller 72 can also include any device capable of analyzing data from various sensors, comparing data, making the necessary decisions required to control and monitor the diverter valve 64, the variable intake valve activation system 22, the turbocharger 18, the aftertreatment device 42, etc.

Communication between controllers, and communication between controllers, actuators and/or sensors may be accomplished using a direct wired link, a networked communications bus link, a wireless link or any another suitable communications link. Communication includes exchanging data signals in any suitable form, including, for example, electrical signals via a conductive medium, electromagnetic signals via air, optical signals via optical waveguides, and the like. The term ‘model’ refers to a processor-based or processor-executable code and associated calibration that simulates a physical existence of a device or a physical process.

The controller 72 includes the processor 74 and tangible, non-transitory memory 76 on which is recorded executable instructions. The controller 72 is configured to control the variable intake valve activation system 22 and the diverter valve 64 to route the recirculated exhaust gas 41. This includes the controller 72 configured to actuate the diverter valve 64 in the first position to route the recirculated exhaust gas 41 toward the aftertreatment device 42 and bypass the dedicated-cylinder EGR system 60, and also configured to actuate the diverter valve 64 in the second position to route the recirculated exhaust gas 41 through the dedicated-cylinder EGR system 60 back to the air intake system 14.

The engine subassembly 12, variable intake valve activation system 22 and dedicated-cylinder EGR system 60 that is described with reference to FIG. 1 can be advantageously controlled to achieve combustion stability across the engine speed/load operating range. The control of the variable intake valve activation system 22 is executed to generate a suitable level of turbulence within each cylinder during the intake stroke to achieve in-cylinder mixing and turbulence that results in a flame propagation speed sufficiently fast to maintain combustion stability at an acceptable level. The in-cylinder mixing and required turbulence level can be accomplished and varied by selectively controlling openings and closings of the first and second intake valves 23, 24, employing the variable intake valve activation system 22.

One combustion parameter associated with combustion stability is a coefficient of variation of indicated mean effective pressure (CoV-IMEP), which can be determined and monitored employing a suitable cylinder monitoring scheme, such as by use of information derived from the combustion sensor 17, an in-cylinder pressure sensor, or another suitable monitoring device. Devices, control routines, calibrations and other elements associated with determining the CoV-IMEP are known to one of ordinary skill in the art, and thus not described in additional detail. This operation is intended to improve overall repeatability and robustness of the entire combustion process, resulting in smooth, consistent engine operation as measured by such parameters as coefficient of variation of indicated mean effective pressure (CoV-IMEP). In one embodiment, the combustion stability may be determined during on-going engine operation by monitoring inputs from the combustion sensor 17 and other engine parameters. Alternatively or in combination, the combustion stability at different speed/load engine operating points may be predetermined during engine development.

The engine controller 72 preferably employs a calibration to command operation of the variable intake valve activation system 22 to achieve preferred opening and closing times or deactivations for the first and second intake valves 23, 24 based upon monitored parameters associated with the engine speed and load. This may be in the form of a feed-forward control routine. The calibration that may be employed herein determines the preferred opening and closing times and/or deactivations for the first and second intake valves 23, 24 that achieve high efficiency with an acceptable level of combustion stability during operation of the engine 10 described with reference to FIG. 1, for each speed/load operating point over a range of engine operation. This may include developing an engine calibration routine that provides preferred opening and closing times and/or deactivations for the first and second intake valves 23, 24 for each speed/load operating point over a range of engine speed/load operating points from idle to a maximum power condition. Alone, or in combination with the feed-forward control routine, the engine controller 72 may execute a feedback control routine to command operation of the variable intake valve activation system 22 to achieve preferred opening and closing times or deactivations for the first and second intake valves 23, 24 based upon monitored parameters associated with the engine speed and load and combustion stability that may be determined during on-going engine operation by monitoring inputs from the combustion sensor 17 and/or other engine parameters. The terms “calibration”, “calibrate”, and related terms refer to a result or a process that compares an actual or standard measurement associated with a device with a perceived or observed measurement or a commanded position. A calibration as described herein can be reduced to a storable parametric table, a plurality of executable equations or another suitable form.

FIG. 2-1 graphically shows a first profile 210 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1, wherein the engine 10 is operating in a four-stroke cycle that includes repetitively occurring exhaust-intake-compression-power strokes that are associated with the reciprocating movement of the pistons and rotation of the crankshaft. The graph includes a magnitude of valve lift on the vertical axis 204 in relation to engine crankshaft rotation (degrees) on the horizontal axis 205. Relevant timings of cylinder positions are indicated, including a first cylinder bottom-dead-center (BDC) point 201 at start of an exhaust stroke, a cylinder top-dead-center (TDC) point 202 at the end of the exhaust stroke, and a second BDC point 203 at the end of the intake stroke. The first profile 210 indicates an exhaust valve opening 215, which is following by simultaneous and equivalent openings of the first intake valve 213 and the second intake valve 214. Control of the variable intake valve activation system 22 of the engine 10 in response to the first profile 210 results in a nominal magnitude of air flow coupled with a nominal level of in-cylinder mixing.

FIG. 2-2 graphically shows a second profile 220 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1. The second profile 220 indicates the exhaust valve opening 215, which is following by simultaneous and equivalent openings of the first intake valve 223 and the second intake valve 224. As shown the open times of the first intake valve 223 and the second intake valve 224 are extended such that they extend into the beginning of a subsequent compression stroke, which may be described as a Miller cycle operation, or an Atkinson cycle operation. An alternate profile could employ valve open times that terminate prior to the end of the intake stroke achieving a similar effect. The Miller cycle may be associated with operation of an internal combustion engine that employs a turbocharger or a supercharger to boost flow of the intake air, and includes either a late intake valve closing event (after BDC) or an early intake valve closing event (before BDC). The Atkinson cycle may be associated with operation of an internal combustion engine that is naturally aspirated. The effect of such operation is to reduce the effective compression ratio. By way of example, during operation with the second profile 220, the piston compresses the fuel-air mixture during the compression stroke only after the intake valves close. During the initial portion of the compression stroke, the piston pushes part of the fuel-air mixture through the still-open intake valve, and back into the intake manifold. When the intake air is cooled by an intercooler, e.g., the charge air cooler 28, there is a resulting lower intake charge temperature. The lower intake charge temperature in combination with the lower compression of the intake stroke may yield a lower final charge temperature than would be obtained by simply increasing the compression of the piston. This allows the ignition timing to be advanced before the onset of detonation, thus increasing overall efficiency. A lower final charge temperature may reduce formation of engine emissions.

FIG. 2-3 graphically shows a third profile 230 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1. The third profile 230 indicates the exhaust valve opening 215, which is following by opening of the first intake valve 233, with the second intake valve 234 deactivated. The effect of such operation is to increase velocity of the intake air flowing through the one open valve and increase the in-cylinder mixing and turbulence by an amount that is greater than the nominal level of in-cylinder mixing described with reference to FIG. 2-1. Furthermore, the in-cylinder turbulence is asymmetric, due to the asymmetric locations of the first and second intake valves 23, 24, which are not arranged in a manner that is co-axial a longitudinal axis of the respective combustion chamber 15.

FIG. 2-4 graphically shows a fourth profile 240 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1. The fourth profile 240 indicates the exhaust valve opening 215, which is following by opening of the first intake valve 243, with the second intake valve 244 deactivated. As shown the open time of the first intake valve 243 is extended such that its opening extends into the beginning of a subsequent compression stroke, i.e., a Miller cycle operation or an Atkinson cycle operation. The effect of such operation is to increase velocity of the intake air flowing through the one open valve and increase the in-cylinder mixing and turbulence by an amount that is greater than the nominal level of in-cylinder mixing described with reference to FIG. 2-1. Furthermore, the in-cylinder turbulence is asymmetric, due to the asymmetric locations of the first and second intake valves 23, 24. As a result of the operation, the ignition timing may be advanced before the onset of detonation, thus increasing overall efficiency. A lower final charge temperature may reduce formation of engine emissions.

FIG. 2-5 graphically shows a fifth profile 250 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1. The fifth profile 250 indicates the exhaust valve opening 215, which is following by opening of the second intake valve 254, with the first intake valve 253 deactivated. This operation is analogous to the third profile 230, and may be selected based upon testing that indicates the resulting in-cylinder mixing and turbulence maintains combustion stability at a suitable level for one or more engine speed/load operating points.

FIG. 2-6 graphically shows a sixth profile 260 in the form of a valve opening timing chart that may be employed to control an embodiment of the engine 10 described with reference to FIG. 1. The sixth profile 260 indicates the exhaust valve opening 215, which is following by opening of the second intake valve 264, with the first intake valve 263 deactivated. The opening of the second intake valve 264 is extended such that its opening extends into the beginning of a subsequent compression stroke, i.e., a Miller cycle operation or an Atkinson cycle operation. The effect of such operation is to increase velocity of the intake air flowing through the one open valve and increase the in-cylinder mixing and turbulence by an amount that is greater than the nominal level of in-cylinder mixing described with reference to FIG. 2-1. This operation is analogous to the fourth profile 240, and may be selected based upon testing that indicates the resulting in-cylinder mixing and turbulence maintains combustion stability at a suitable level for one or more engine speed/load operating points.

The concepts described herein promote optimum efficiency of an embodiment of the engine 10 described with regard to FIG. 1 through the use of two intake valve events that are characterized by valve opening, including a four-cycle event and, by way of a non-limiting example, a Miller cycle event. Additional efficiency gains may be achieved at low load conditions by deactivating one of the intake valves 23, 24 to increase combustion system charge motion.

The detailed description and the drawings or figures are supportive and descriptive of the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments for carrying out the present teachings have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims.

Claims

1. A multi-cylinder internal combustion engine system, comprising:

an engine subassembly including an engine block defining a plurality of cylinders and a plurality of first and second intake valves disposed in a cylinder head between an air intake system and the cylinders;

a dedicated-cylinder exhaust gas recirculation (EGR) system including an exhaust runner fluidly connected between an exhaust valve of one of the cylinders and the air intake system of the engine;

a controllable intake valve activation system configured to control openings of the plurality of first and second intake valves;

a controller operatively connected to the internal combustion engine and the controllable intake valve activation system, the controller including an instruction set, the instruction set executable to: monitor of a parameter associated with combustion stability in the engine, and operate the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves, wherein the openings of the first and second intake valves are selected to achieve combustion stability in the engine.

2. The engine system of claim 1, wherein the instruction set is further executable to:

monitor operation of the engine to determine an engine speed/load operating point, and control the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves to achieve combustion stability at the engine speed/load operating point.

3. The engine system of claim 2, wherein the instruction set executable to control the controllable intake valve activation system to control openings of the first and second intake valves and control openings of the second intake valves to achieve combustion stability at the engine speed/load operating point comprises a calibration that includes preferred openings of the first and second intake valves based upon the engine speed/load operating point.

4. The engine system of claim 1, wherein the instruction set executable to control the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves comprises the instruction set being executable to control the controllable intake valve activation system to open both the first intake valve and the second intake valve during each intake stroke of each combustion cycle.

5. The engine system of claim 1, wherein the instruction set executable to control the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves comprises the instruction set being executable to control the controllable intake valve activation system to open only the first intake valve.

6. The engine system of claim 5, further comprising the instruction set being executable to control the controllable intake valve activation system to open only the first intake valve during each intake stroke of each combustion cycle, wherein open time of the first intake valve is extended to effect valve closing during a subsequent compression stroke.

7. The engine system of claim 5, further comprising the instruction set being executable to control the controllable intake valve activation system to open only the first intake valve during each intake stroke of each combustion cycle, wherein open time of the first intake valve is reduced to effect valve closing prior to the end of the intake stroke.

8. The engine system of claim 1, wherein the instruction set executable to control the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves comprises the instruction set being executable to control the controllable intake valve activation system to open only the second intake valve during each intake stroke of each combustion cycle.

9. The engine system of claim 8, wherein the instruction set is further executable to control the controllable intake valve activation system to open only the second intake valve during each intake stroke of each combustion cycle, wherein open time of the second intake valve is extended to effect valve closing during a subsequent compression stroke.

10. The engine system of claim 8, wherein the instruction set is further executable to control the controllable intake valve activation system to open only the second intake valve during each intake stroke of each combustion cycle, wherein open time of the second intake valve is reduced to effect valve closing prior to the end of the intake stroke.

11. A method for operating a multi-cylinder internal combustion engine that includes a variable intake valve activation system and a dedicated-cylinder exhaust gas recirculation (EGR) system, the method comprising:

monitoring an engine parameter associated with combustion stability during operation of the dedicated-cylinder EGR system; and

controlling, by a controller, the variable intake valve activation system to control opening of a first intake valve and control opening of a second intake valve to achieve combustion stability.

12. The method of claim 11, further comprising:

monitoring operation of the engine to determine an engine speed/load operating point, and

controlling the controllable intake valve activation system to control openings of the first intake valves and control openings of the second intake valves to achieve combustion stability at the engine speed/load operating point.

13. The method of claim 12, wherein controlling the controllable intake valve activation system comprises a calibration that includes preferred openings of the first and second intake valves based upon the engine speed/load operating point.

14. The method of claim 11, wherein controlling the controllable intake valve activation system comprises opening both the first intake valve and the second intake valve during each intake stroke of each combustion cycle.

15. The method of claim 11, wherein controlling the controllable intake valve activation system comprises opening only the first intake valve during each intake stroke of each combustion cycle.

16. The method of claim 15, further comprising controlling the controllable intake valve activation system to open only the first intake valve during each intake stroke of each combustion cycle, wherein the opening of the first intake valve is extended to end during a subsequent compression stroke.

17. The method of claim 15, further comprising controlling the controllable intake valve activation system to open only the first intake valve during each intake stroke of each combustion cycle, wherein the opening of the first intake valve is reduced to end during the intake stroke.

18. The method of claim 11, wherein controlling the controllable intake valve activation system comprises opening only the second intake valve during each intake stroke of each combustion cycle.

19. The method of claim 18, further comprising opening only the second intake valve during each intake stroke of each combustion cycle, wherein opening of the second intake valve is extended to end during a subsequent compression stroke.

20. The method of claim 18, further comprising opening only the second intake valve during each intake stroke of each combustion cycle, wherein the opening of the second intake valve is reduced to end during the intake stroke.