Patent Description:
The quantity of nitrogen oxides (NOx) generated during operation of internal combustion engines, including, for example, lean burn spark engines, can be attributed, at least in part, to in-cylinder temperatures. Accordingly, certain attempts to control NOx generation have included controlling the temperature of the associated combustion event and/or the in-cylinder temperature. Other systems may attempt to control in-cylinder temperatures by controlling in-cylinder pressure and/or flame speeds.

In-cylinder temperatures and the properties of the fuel that is utilized during combustion events can also generally be correlated to the presence, and potential increases, of engine knock. Moreover, as in-cylinder temperatures increase, both the instances of engine knock and the quantity of generated NOx can also increase. While engine knock can be attributed to a variety of factors, for at least certain types of fuel used with lean burn spark engines, such as, for example, engines that utilize natural gas as a fuel, engine knock can be attributed to changes in fuel properties. Such changes in fuel properties can include, but is not limited to, a methane number (MN) of a natural gas fuel and the presence and/or quantity of diluents in fuel, such as CO<NUM>, among other diluents.

Current control strategies that attempt to reduce NOx generation in lean burn spark ignition engines often target a fixed NOx level. Such strategies can include sensing a NOx level, such as, for example, by NOx sensors, and, if necessary and based on the sensed NOx levels, adjusting the air-to-fuel mixture delivered to the cylinders in at least an attempt to adjust the NOx levels. Other approaches may also be employed that estimate the NOx level, such as, for example, a Torque Over Boost (TOB) method. Yet, such controls may not accommodate, or adjust to, changes in certain conditions, such as, for example, a change in one or more properties of the fuel being supplied for combustion in the engine. Moreover, such changes in the property(ies) of the fuel can adversely impact efforts to adjust operations of the engine system that seek to adjust NOx levels.

Further, current controls often change or adjust certain engine operations based at least in part on engine knock margin. However, the different manners in which NOx and engine knock levels have been controlled often results in conflict between the control strategies for NOx levels and the control strategies for engine knock. Moreover, the control strategies for controlling NO x levels and for controlling engine knock levels can fight each other as the strategies attempt to attain target NOx and/or engine knock levels. Such conflicts can adversely impact not only the ability to attain such target levels, but can also adversely impact operation of the internal combustion engine.

<CIT> discloses an internal combustion engine control apparatus having a digital arithmetic unit to which signals are inputted from a plurality of detectors such as detectors for detecting an operational state of the engine and air fuel ratio detector and controls a fuel air ratio and ignition timing according to output signals from the arithmetic unit. The apparatus comprises by a misfire detector for detecting a misfiring state of the engine, NOx concentration detector and a controller for controlling the fuel air ratio and the ignition timing so as to fall within a tolerable stable combustion range defined by a detected misfire boundary and a detected NOx limit. The misfiring state and/or NOx concentration can be detected through detection of temperature change in the combustion chamber by a detector. The detector comprises a black body disposed in the combustion chamber and a fused silica cable mounting the black body. <CIT> discloses a sensor that detects the rotational speed and load of the engine, a means for calculating an injection amount to obtain an air-fuel ratio leaner than the stoichiometric air-fuel ratio from these detected values, and a means for calculating the basic air-fuel ratio from both detected values. A means for calculating the target ignition timing from both detected values, a sensor for detecting the cylinder pressure, and a crank angle position at which the cylinder pressure detection value is maximum is a certain crank angle position after compression top dead center. Means for correcting the target ignition timing to determine the actual ignition timing to be output to the ignition device.

An aspect of an embodiment of the present application is a system according to claim <NUM>.

Another aspect of an embodiment of the present application is a method according to claim <NUM>.

The description herein makes reference to the accompanying figures wherein like reference numerals refer to like parts throughout the several views.

The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentalities shown in the attached drawings. Further, like numbers in the respective figures indicate like or comparable parts.

Certain terminology is used in the foregoing description for convenience and is not intended to be limiting. Words such as "upper," "lower," "top," "bottom," "first," and "second" designate directions in the drawings to which reference is made. This terminology includes the words specifically noted above, derivatives thereof, and words of similar import. Additionally, the words "a" and "one" are defined as including one or more of the referenced item unless specifically noted. The phrase "at least one of" followed by a list of two or more items, such as "A, B or C," means any individual one of A, B or C, as well as any combination thereof.

Embodiments of the present application include a control strategy that can at least assist in maintaining engine knock and NOx emissions below corresponding threshold limits, while also being capable of automatically adjusting to changes in fuel properties, such as, for example, changes in the methane number or diluent(s) of/in a natural gas fuel that is utilized at least in the in-cylinder combustion event. Embodiments of the present application can also be configured to prevent or minimize conflicts between adjustments in the operation of an engine associated with engine knock and NOx emissions, and may also be configured to seek to generally maintain a relatively constant spark timing level or value and/or maximize the brake thermal energy (BTE) of the engine with the associated fuel.

<FIG> illustrates a schematic block diagram of an exemplary internal combustion engine system <NUM> that includes a lean burn spark ignition engine <NUM> that is connected to an intake system <NUM> and an exhaust system <NUM>. It shall be appreciated that the illustrated configuration and components of the engine system <NUM> are but one example, and that the disclosure contemplates that a variety of different engine systems and the associated components may be utilized. Further, the engine system <NUM> may be used in a variety of different applications or platforms, and moreover with a variety of different types of machines, vehicles, and/or devices, including, but not limited to, stationary devices as well as on-road vehicles, including automotive applications. The engine <NUM> can receive fuel from one or more fuel sources <NUM>. Further, while the illustrated embodiment may generally depict an engine system <NUM> used with lean burn spark ignition engine applications, the engine system <NUM> can be structured to operate with a variety of types of fuels that are delivered from the fuel source <NUM>, including, for example, natural gas, bio-gas, methane, propane, gasoline, ethanol, producer gas, field gas, liquefied natural gas, compressed natural gas, landfill gas, gaseous fuel, and/or any combination thereof, among other fuels.

According to the exemplary embodiment, the engine <NUM> includes an engine block that may define at least a portion of one or more cylinders. For example, according to certain embodiments, the engine <NUM> can include six or eight cylinders in an in-line arrangement. However, the engine <NUM> may have any different number of cylinders, as well as cylinders in a variety of different arrangements. Additionally, each cylinder is sized to accommodate the slideable displacement of a piston along at least a portion of the cylinder such that the pistons may reciprocate between a top-dead-center position and a bottom-dead-center position. Each of the cylinders, its respective piston and cylinder head, form a combustion chamber. Further, at least a portion of the forces generated by the slideable displacement of the piston along at least a portion of the cylinder during combustion events in the combustion chamber are transmitted to a mechanical drive system <NUM>. For example, the pistons are typically operably coupled to a crank shaft of a mechanical drive system <NUM> of the engine system <NUM> that converts the reciprocal movement of the pistons of the engine <NUM> into rotational movement.

The cylinders are in selective fluid communication with the intake system <NUM> such that a charged air flow can be delivered to the combustion chamber. The cylinders are also in selective fluid communication with the exhaust system <NUM> such that exhaust gases produced by combustion of fuel(s) in the combustion chambers can be delivered through an exhaust manifold <NUM> of the exhaust system <NUM>. The exhaust system <NUM> can include and/or be coupled to a variety of different components, such as, for example, one or more turbochargers 114a, 114b, as well as an after-treatment system <NUM>.

Operation of fuel injection events can include the delivery of charge flow and fuel to the combustion chambers of the engine <NUM>. According to certain embodiments, fuel, such as, for example, a natural gas, can be fumigated into the charge flow upstream of the cylinders of the engine <NUM>, such as, for example, upstream or downstream of the compressor 114a, at the intake manifold <NUM>, and/or cylinder ports, or can be fumigated into the charge mixture in-cylinder. The delivery of the charge mixture and/or the fuel into the combustion chambers may be, at least in part, electrically controlled by a control system <NUM> of the engine system <NUM>.

The control system <NUM> can include a controller <NUM> that can be configured to control various operational aspects of engine system <NUM>, including fuel injection events, among other operations. The controller <NUM> can be implemented in a number of ways. Further, the controller <NUM> can execute operating logic that defines various control, management, and/or regulation functions. The operating logic may be in the form of one or more microcontroller or microprocessor routines stored in a non-transitory memory, dedicated hardware, such as a hardwired state machine, analog calculating machine, various types of programming instructions, and/or other forms as would occur to those skilled in the art.

The controller <NUM> may be provided as a single component, or a collection of operatively coupled components, and may comprise digital circuitry, analog circuitry, or a hybrid combination of both of these types. When of a multi-component form, the controller <NUM> may have one or more components remotely located relative to the others in a distributed arrangement. The controller <NUM> can include multiple processing units arranged to operate independently, in a pipeline processing arrangement, in a parallel processing arrangement, or the like. In one embodiment, the controller <NUM> includes several programmable microprocessing units of a solid-state, integrated circuit type that are distributed throughout the engine system <NUM> that each includes one or more processing units and non-transitory memory. For the depicted embodiment, the controller <NUM> includes a computer network interface to facilitate communications using standard Controller Area Network (CAN) communications or the like among various system control units. It should be appreciated that the depicted modules or other organizational units of the controller <NUM> refer to certain operating logic performing indicated operations that may each be implemented in a physically separate controller of the controller <NUM> and/or may be virtually implemented in the same controller.

The description herein including modules and/or organizational units emphasizes the structural independence of the aspects of the controller <NUM>, and illustrates one grouping of operations and responsibilities of the controller <NUM>. Other groupings that execute similar overall operations are understood within the scope of the present application. Modules and/or organizational units may be implemented in hardware and/or as computer instructions on a non-transient computer readable storage medium, and may be distributed across various hardware or computer based components.

Example and non-limiting implementation elements of modules and/or organizational units of the controller <NUM> include sensors of a sensor system <NUM> providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements.

The controller <NUM> and/or any of its constituent processors/controllers may include one or more signal conditioners, modulators, demodulators, Arithmetic Logic Units (ALUs), Central Processing Units (CPUs), limiters, oscillators, control clocks, amplifiers, signal conditioners, filters, format converters, communication ports, clamps, delay devices, memory devices, Analog to Digital (A/D) converters, Digital to Analog (D/A) converters, and/or different circuitry or functional components as would occur to those skilled in the art to perform the desired communications.

Referencing <FIG>, according to the certain embodiments, the controller <NUM> can include a spark timing module <NUM> and an air-to-fuel module <NUM>. According to such an embodiment, the spark timing module <NUM> can be configured to adjust spark timing to attain an engine knock and/or NOx target level, while the air-to-fuel module <NUM> can be adapted to modify an air-to-fuel ratio to bring spark timing back to a target level or value. Further, according to certain embodiments, adjustments to spark timing, as determined using the spark timing module <NUM>, can be implemented prior to implementation of adjustments to the air-to-fuel ratio, as determined by the air-to-fuel module <NUM>. While <FIG> illustrates the spark timing module <NUM> and the air-to-fuel module <NUM>, as well as the associated components, as separated components, according to other embodiments at least some of these components may each be part of the same component or part of other components of the controller <NUM>. Further, the controller <NUM> can, according to other embodiments, include other modules and/or controllers in addition to those illustrated in <FIG>.

According to the illustrated embodiment, the spark timing module <NUM> can include a NOx feedback controller <NUM>, a knock index controller <NUM>, and a moderator module <NUM>. The NOx feedback controller <NUM> can be configured to determine adjustments to spark timing, among other adjustments, that can at least assist the engine <NUM> in attaining, or being closer to, a target NOx level. According to the illustrated embodiment, the NOx feedback controller <NUM> can be electrically coupled to a first comparator <NUM>, also referred to as an NOx comparator, that is configured to evaluate a first NOx level (referred to in <FIG> as "Measured NOx") with a NOx target value (referred to in <FIG> as "NOx Target"). According to certain embodiments, the first NOx level can correspond to an actual, predicted, or estimated NOx level associated with the operation of the engine <NUM>. For example, the first comparator <NUM> may be operably coupled to one or more NOx sensors <NUM> that can be positioned at a variety of locations about the engine system <NUM>. For example, according to certain embodiments, the NOx feedback controller <NUM> can be in electrical communication with a NOx sensor <NUM> that is positioned to detect NOx in an exhaust gas that has been released from the engine <NUM> and/or cylinders, including one or more NOx sensors that may be positioned upstream, at, and/or downstream of an exhaust manifold <NUM>, turbine 114b, and/or exhaust after treatment system <NUM>, among other locations. Additionally, or alternatively, the first NOx level can be a NOx level that is predicted or estimated based on other measured or predicted operating conditions or parameters, including, for example, exhaust gas temperature, and in-cylinder pressure, among other conditions or parameters. Further, for example, according to certain embodiments, the first NOx level can be a model NOx level that is based, at least in part, on information provided by one or more sensors, measurements, and/or models in addition to, or, alternatively in lieu of, an actual NOx value(s). For example, according to certain embodiments, determination of NOx levels can be attained through the use of a Torque over Boost (TOB) approach, thereby providing a virtual NOx sensor that can replace a NOx sensor <NUM> and/or be used as a backup in the event that the NOx sensor(s) <NUM> fails. According to certain embodiments, the target NOx level or range can be a pre-determined threshold NOx level(s) or range(s). Further, according to certain embodiments, the target NOx level(s) or range(s) can be adjusted based on certain factors, including, for example, engine load and/or engine speed, among other variables.

The first comparator <NUM> can provide an indication to the NOx feedback controller <NUM> of the difference(s), if any, between the first NOx level and the target NOx level. The NOx feedback controller <NUM> can be structured to determine, based at least in part on the information from the first comparator <NUM> regarding differences in the first and target NOx levels, adjustments to spark timing that can bring the level of NOx being generated by operation of the engine <NUM> generally closer to, within, and/or below, the target NOx level. Such adjustments can include, but are not limited to, adjusting spark timing, including, for example, retarding or advancing spark timing, so as to either reduce or increase the level of NOx being generated by operation of the engine <NUM>.

The knock index controller <NUM> can be adapted to determine adjustments to spark timing, among other adjustments, that can at least assist the engine system <NUM> with being generally closer to, within, and/or below an engine knock threshold limit(s) or range(s). According to the illustrated embodiment, the knock index controller <NUM> can be electrically coupled to a second comparator <NUM>, also referred to as a knock level comparator, that is configured to evaluate a first engine knock level (referred to in <FIG> as a measured knock voltage) with an engine knock target value (referred to in <FIG> as knock voltage target). Further, according to certain embodiments, the first engine knock level can correspond to an actual, predicted, or estimated engine knock level associated with the operation of the engine <NUM>. For example, the second comparator <NUM> can be operably coupled to one or more knock sensors, knock vibration sensors, temperature sensors, and/or in-cylinder pressure sensors, among other sensors. Moreover, according to certain embodiments, the second comparator <NUM> may be part of, or in communication with, a knock control system that may, with the use of a knock and/or vibration sensor <NUM>, detect and analyze vibrations and/or noises in the engine system <NUM> associated with the operation of one or more components of the engine system <NUM>. The second comparator <NUM> and/or controller <NUM>, among other components, may further be adapted to track or maintain one or more records pertaining to the detected, determined, and/or predicted occurrences of engine knock during the course of one or more time periods. Thus, according to certain embodiments, the second comparator <NUM> may be in electrical communication with a timer <NUM> of the controller <NUM> that can indicate the timing of an actual and/or predicted engine knock, a period of time between one or more actual and/or predicted engine knocks, and/or the number of predicted and/or actual engine knocks over the course of a time period(s). Accordingly, the second comparator <NUM> and/or another component of the controller <NUM> can be adapted to determine whether one or more characteristics of a detected and/or predicted engine knock, or plurality of engine knocks, does or does not meet or exceed a threshold knock limit. For example, the second comparator <NUM> may determine whether the number of detected and/or predicted engine knocks in a given time period does or does not exceed a knock margin or other knock threshold value and/or is or is not close to a threshold engine knock value. According to certain embodiments, the target engine knock level can be a pre-determined threshold engine knock level(s) or range(s). Further, according to certain embodiments, the target engine knock level(s) or range(s) can be adjust based on certain factors, including, for example, engine load and/or engine speed, among other variables.

The second comparator <NUM> can provide an indication to the knock index controller <NUM> of the difference(s), if any, between the first engine knock level and the target engine knock level. The knock index controller <NUM> can be structured to determine, based at least in part on the information from the second comparator <NUM> regarding differences in the first and target engine knock levels, adjustments to spark timing that can bring the level of engine knocks being generated by operation of the engine <NUM> to a level that is generally closer, within, and/or below, the target engine knock level(s) or range(s). Such adjustments can include, but are not limited to, adjusting spark timing, including, for example, advancing or retarding spark timing. For example, similar to the NOx feedback controller <NUM>, in at least certain situations, the knock index controller <NUM> can determine an adjustment in the spark timing event that can bring engine knock levels closer to a threshold engine knock limit, and which involves the retarding or advancing of the spark timing so as to either reduce or increase the level of knock being generated by operation of the engine <NUM>.

According to the certain embodiments, the moderator module <NUM> can be adapted to evaluate at least certain aspects of the instructions or information provided by the NOx feedback controller <NUM> and the knock index controller <NUM>. Moreover, the moderator module <NUM> can be adapted to resolve potential conflicts that may be presented by, or created by, the instructions or information provided by the NOx feedback controller <NUM> and the knock index controller <NUM> in connection with their its attempts to adjust engine operations to adjust NOx levels and engine knock levels, respectively. According to the illustrated embodiment, the moderator module <NUM> may be adapted to evaluate at least certain aspects of the instructions or information provided by the NOx feedback controller <NUM> and the knock index controller <NUM>, and based on that evaluation, select the information or instructions from one, and only one, of the NOx feedback controller <NUM> and the knock index controller <NUM> for implementation by the controller <NUM>, engine <NUM>, and/or engine system <NUM>. Additionally, according to certain embodiments, the one or more characteristics evaluated by the moderator module <NUM> may be based on which instructions or information from the NOx feedback controller <NUM> and the knock index controller <NUM> the moderator module <NUM> determines can facilitate the largest retardation of combustion events. Moreover, according to certain embodiments, selection of the instructions or information from the one of the NOx feedback controller <NUM> and the knock index controller <NUM> that can result in the largest retardation of the combustion event can be selected. Such an approach can, in at least certain situations, be viewed as having a greater likelihood attaining both NOx levels and engine knock levels that are within and/or below associated threshold levels. Further, in at least certain situations, as NOx and engine knock levels may rise and fall together, albeit at different slopes, such an approach of adjusting spark timing based on the instructions or information from one of the NOx feedback controller <NUM> and the knock index controller <NUM> may allow one of the NOx level and engine knock level to be around, or relatively close to, the corresponding threshold level, while the other of the NOx and engine knock levels can below the associated threshold level. Additionally, upon selection and implementation of the selected information and/or instructions, according to certain embodiments, the moderator module <NUM> may, or may not, be configured to control subsequent attempts by the NOx feedback controller <NUM> and/or the knock index controller <NUM> to further adjust spark timing.

According to the illustrated embodiment, information or instructions communicated from the mediator module <NUM> can be communicated to a third, adjusted spark timing comparator <NUM>. According to the illustrated embodiment, the third, adjusted spark timing comparator <NUM> can compare the adjustment spark timing associated with the information or instructions selected by the moderator module <NUM>, with a base spark timing value (shown in <FIG> as "Base ST"). For example, according to certain embodiments, the base spark timing value can be a standard angular position of a piston in a cylinder when a spark event is to occur, while the adjustment selected by the moderator module <NUM> is a different or adjusted angular position of the piston in the cylinder when the spark event is to occur. According to such an embodiment, the differences, if any, in the adjusted spark timing associated with the information or instructions selected by the moderator module <NUM> and the base spark timing can be communicated to a charge flow controller <NUM>.

The charge flow controller <NUM> can, at least in part, be adapted to provide instructions to adjust the operation of certain components of the engine <NUM> and/or engine system <NUM> so as to adjust the air-to-fuel mixture and/or spark timing. For example, according to certain embodiments, in response to instructions or information from the spark timing module <NUM> and/or the third comparator <NUM>, the charge flow controller <NUM> can communicate instructions to adjust when a spark plug(s) in one or more cylinders is to provide a spark and/or the timing at which power is provided to the spark plug(s) to initiate a spark event. Thus, with respect to at least the operation of the spark timing module <NUM>, the charge flow controller <NUM> can adjust when the operation of certain components associated with providing a spark in the cylinder so as to advance or retard spark timing in accordance with instructions or information from the spark timing module <NUM>, and thereby bring one or both of the NOx level(s) and engine knock level(s) to, around, or below associated target threshold levels.

<FIG> provides a flow diagram of an exemplary process <NUM> of operation of a spark timing module <NUM> in the selection of proposed instructions or information from the NOx feedback controller <NUM> and the knock index controller <NUM> for implementation in adjusting one or more operations and/or characteristics of the engine system <NUM>, including, for example, adjusting spark timing. The operations illustrated for all of the processes in the present application are understood to be examples only, and operations may be combined or divided, and added or removed, as well as re-ordered in whole or in part, unless explicitly stated to the contrary.

At step <NUM>, the engine system <NUM> can determine or detect that one or more characteristics relating to the operation of the engine system <NUM> does, or is predicted to, not satisfy a particular value(s) or range of values, including, for example, not being below a certain threshold value(s) or range of values. For example, referencing <FIG>, such a determination can be the first comparator <NUM> determining the first NOx level is outside or away from the threshold for a target NOx level(s) or range(s) and/or by the second comparator <NUM> determining that the first engine knock level is outside or away from a threshold for a target engine knock level(s) or range(s). At step <NUM>, information indicating differences between the NOx and/or engine knock level(s) or range(s) and associated threshold level(s) or range(s) can be utilized by the associated NOx feedback controller <NUM> and the knock index controller <NUM> to determine an adjustment(s) in spark timing that could at least assist in the bringing the corresponding NOx and/or engine knock levels to closer to and/or within threshold levels. For example, the NOx feedback controller <NUM> can provide instructions that seek to advance or retard spark timing as to either increase or reduce the level of NOx being generated by operation of the engine <NUM>.

At step <NUM>, the proposed instructions or information from one or both of the NOx feedback controller <NUM> and the knock index controller <NUM> can be communicated to the moderator module <NUM>. The moderator module <NUM> can be configured to, at step <NUM>, evaluate the impact the proposed instructions or information from one or more of the NOx feedback controller <NUM> and the knock index controller <NUM> can have on certain aspects of operation of the engine system <NUM>. For example, according to certain embodiments, the moderator module <NUM> can be adapted to evaluate proposed instructions from the knock index controller <NUM> relating to adjusting spark timing, and the effects such adjustments, if implemented, could have on NOx levels and/or engine knock levels. As previously mentioned, according to certain embodiments, such evaluation by the moderator module <NUM> can involve the moderator module <NUM> determining which instructions or information from the NOx feedback controller <NUM> and the knock index controller <NUM>, if implemented, would result in adjustments that facilitate the largest retardation of the combustion event.

At step <NUM>, the moderator module <NUM> can select which instruction or information is to be implemented to adjust certain operations of the engine <NUM> and/or engine system <NUM>. For example, in the illustrated embodiment, the moderator module <NUM> can select at step <NUM> the adjustment that is to be made to spark timing. Again, according to certain embodiments, such selection can involve selecting the instructions or information from one, but not both, of the NOx feedback controller <NUM> and the knock index controller <NUM>. Accordingly, at step <NUM>, the selected information or instructions may be implemented, such as, for example, via instructions provided by the charge flow controller <NUM>. For example, according to certain embodiments, the selected information or instructions can provide an indication to the charge flow controller <NUM> of the degree spark timing is to be either advanced or retarded, which can then be implemented using instructions communicated by the charge flow controller <NUM> for adjustments in the operation of certain components of the engine <NUM> and/or engine system <NUM>.

Referencing <FIG>, according to the claimed invention, the air-to-fuel module <NUM> includes a fourth, spark timing comparator <NUM> and a spark timing controller <NUM>. The fourth comparator <NUM> can evaluate a measured or predicted spark timing (identified as "Measured ST" in <FIG>) and a target spark timing (identified as "Target ST" in <FIG>). According to the claimed invention, the "Measured ST" corresponds to the adjusted spark timing selected by the moderator module <NUM>, as discussed above, for example, at least in connection with steps <NUM> and <NUM> of the process <NUM> depicted in <FIG>. Thus, according to the claimed invention, implementation of changes or adjustments in the operation of the engine <NUM> and/or engine system <NUM> can occur after adjustments to spark timing have been implemented via use of the spark timing module <NUM>. Further, according to certain embodiments, the "Measured ST" and the "Target ST" can correspond to the angular position of a piston within a cylinder at the time of the spark event.

The spark timing controller <NUM> of the air-to-fuel module <NUM> is configured to determine, based on information provided by the fourth comparator <NUM>, changes in an air-to-fuel ratio that can bring the spark timing back to, or around, the target spark timing level. Moreover, in response to at least changes to spark timing that may have occurred in at least an attempt(s) by the spark timing module <NUM> to bring engine knock and/or NOx levels closer to and/or below threshold target levels, the spark timing controller <NUM> can be adapted to use subsequent adjustments in air-to-fuel ratios to at least attempt to retain the adjusted engine knock and/or NOx levels at, around, and/or below, threshold target levels while regaining, or being closer to, target spark timing values. Thus, according to the claimed invention, the spark timing controller <NUM> is adapted to determine an adjustment to the air-to-fuel (lambda) value based on differences between the target spark timing value and the measured or predicted spark timing value, as provided by the fourth comparator, so as to maintain NOx and/or engine knock levels are maintained at, around, or below target threshold values when spark timing is returned to, or around, a target spark timing value(s).

For example, in certain instances in which the spark timing had been retarded, the spark timing controller <NUM> can determine the extent the air-to-fuel ratio is to be leaned, and/or an associated leaner air-to-fuel ratio that can be utilized if and when the spark timing is returned to, or around, the target spark timing value. Similarly, in certain instances in which the spark timing had been advanced, the spark timing controller <NUM> may determine the extent the air-to-fuel ratio is to be richer, and/or an associated richer air-to-fuel ratio, that can be utilized if and when the spark timing is returned to, or around, the target spark timing value. Such changes in air-to-fuel ratio can generally be derived in a manner that can allow spark timing to be maintained at, or brought back to, a relatively constant target spark timing value while engine knock levels and/or NOx levels are at, around, and/or below associated threshold target limits.

According to the illustrated embodiment, the adjusted air-to-fuel ratio (lambda) that is determined by the spark timing controller <NUM> can be provided to a fifth, lambda comparator <NUM>. The fifth comparator <NUM> can be configured to evaluate the adjusted air-to-fuel ratio in relation to a base air-to-fuel ratio (lambda). A variety of different values can be used as the base air-to-fuel ratio (lambda). For example, the base air-to-fuel ratio (lambda) can be a target air-to-fuel ratio or range of values. Further, the base air-to-fuel ratio can be adjustable based on a variety of factors, including, for example, engine load, engine speed, air density, air temperature, and/or fuel properties, among other criteria. Further, according to certain embodiments, the base air-to-fuel ratio can be provided by one or more models, and can be associated with an ideal air-to-fuel ratio. Further, the evaluation of the base air-to-fuel ratio and the adjusted air-to-fuel ratio, as provided by the spark timing controller <NUM>, can derive differences, if any, between those lambda values or other associated values. As depicted by <FIG>, according to certain embodiments, the results, or information pertaining to, the evaluation by the fifth comparator <NUM> can be provided to the charge flow controller <NUM>.

In addition to at least assisting in implementing adjustments selected by the moderator module <NUM>, as previously discussed, the charge flow controller <NUM> can also be adapted, at least in part, to at least assist in the implementation of adjustments based on information derived or provided by the air-to-fuel module <NUM>, including information that is evaluated by the fifth comparator <NUM>. For example, the charge flow controller <NUM> can receive information from the air-to-fuel module <NUM> via the fifth comparator <NUM> relating to adjustments to the air-to-fuel ratio (lambda) and, based on that information or instructions, provide commands that are used to alter or adjust the operation of certain components of the engine <NUM> and/or engine system <NUM> to effectuate such adjustments. For example, according to certain embodiments, the charge flow controller <NUM> can, based at least in-part on information or instructions from the air-to-fuel module <NUM>, issue commands that adjust the amount of fuel that is fumigated into the charge flow and/or the amount of fuel that is delivered into the combustion chamber by a fuel injector or other fuel delivery component, and thereby adjust the air-to-fuel ratio to be richer or leaner. Further, as previously discussed, the charge flow controller <NUM> can also provide instructions that can alter the spark timing, which can include bring or maintaining the spark timing at or around a target spark timing value. For example, information received from the air-to-fuel module <NUM> can include instructions relating to retaining the target spark timing value, including, for example, the degree to which the spark timing is to be adjusted to return to, or be around, the target spark timing value. Alternatively, according to certain embodiments, the charge flow controller <NUM> can be structured to adjust the spark timing to, or around, a target spark timing value(s) in connection with receipt of instructions relating to the air-to-fuel module <NUM> determination of adjustments to the air-to-fuel ratio.

<FIG> illustrates a flow diagram of an exemplary process <NUM> of operation of an air-to-fuel module <NUM> in the adjustment of spark timing to a target value and the associated adjustment of the air-to-fuel ratio so as to maintain one or both of an NOx level and an engine knock level at, around, and/or below a corresponding threshold value. At step <NUM>, an evaluated or measured or predicted spark timing ("ST") can be evaluated relative to a target spark timing. For example, referencing <FIG>, according to the claimed invention, such evaluation involves the fourth, spark timing comparator <NUM> determining differences, such as, but not limited to, a measured or predicted and a target angular position of a piston within a cylinder at the time of the spark event. Further, as previously discussed, according to the claimed invention the measured or predicted spark timing is the adjusted spark timing selected by the moderator module <NUM>, as discussed, for example, with respect to at least steps <NUM> and <NUM> of the process <NUM> depicted in <FIG>.

At step <NUM>, based at least in part on the results of the evaluation at step <NUM>, a determination can be made as to what changes or adjustments to the spark timing will bring the spark timing back to, or around, the target spark timing value. For example, according to certain embodiments, a determination at step <NUM> can be that the measured or predicted angular position of a piston within a cylinder at the time of the spark event spark timing is a certain number of degrees less or greater than the target angular position of the piston at the time of the spark event. According to such a situation, the results of the determination at step <NUM> can be used at step <NUM> to determine the extent the spark timing value is to be adjusted to attain or maintain the target spark timing. In connection with the determined adjustment of the spark timing value, at step <NUM> a determination can be made as to an adjustment(s) in the air-to-fuel ratio (lambda) that can at least assist in retaining NOx and/or engine knock levels at or below associated threshold target values in view of adjustments, as determined at step <NUM>, that can bring the sparking timing value back to, or around, the target spark timing value. For example, as previously mentioned, such adjustments at step <NUM> can involve determining the extent the air-to-fuel ratio is to be leaned, and/or an associated leaner air-to-fuel ratio, if the spark timing value is being returned to the target spark timing value from a retarded spark timing value. Similarly, such a determination at step <NUM> can involve determining the extent the air-to-fuel ratio is to be richer, and/or an associated richer air-to-fuel ratio, if the spark timing value is returning to the target spark timing value from an advanced spark timing value.

At step <NUM>, according to certain embodiments, the adjusted air-to-fuel ratio can be compared to a base air-to-fuel ratio. According to certain embodiments, the base air-to-fuel ratio can vary based on a number of factors, including, for example, current operating demands and/or conditions of the engine <NUM> and/or engine system <NUM>, as well as ambient conditions, among other factors. According to certain embodiments, such a comparison can indicate the degree or amount, if any, that the air-to-fuel ratio being used in the operation of the engine <NUM> is to be adjusted. At step <NUM>, the results of the evaluation, such as, for example, the results of the comparison between the base air-to-fuel ratio and the adjusted air-to-fuel ratio, can be provided for implementation. For example, according to the embodiment of a controller <NUM> discussed above with respect to <FIG>, implementation of such an adjustment, if any, can be communicated via commands from the charge flow controller <NUM> and implemented by various components of the engine system <NUM> and/or engine <NUM> that can adjust the charge flow and/or the delivery or injection of fuel that is used for the combustion event.

<FIG> illustrates an exemplary graphical representation of certain control strategies of an embodiment of the present application that initially controls spark timing to control certain levels, and subsequently adjusts an air-to-fuel ratio to continue to control those levels while bringing spark timing back to a target value. In the illustrated graph, the dashed horizontal line extending through the middle of the graph indicates knock level, with an intersecting dashed line that also extends through the middle of the graph indicating a knock limit threshold. Additionally, the horizontal axis provides an indication of the effect of fast spark timing control on engine knock, with the intersecting vertical axis providing an indication of average spark timing.

As shown by the example depicted in <FIG>, a current operating point P1 is at a level in which the average spark timing is generally at or around a target spark timing value, but the engine knock level exceeds the threshold "knock limit". Accordingly, in such a situation, as discussed above, the spark timing module <NUM>, including, for example, the NOx feedback controller <NUM>, can provide instructions or information to the moderator module <NUM> regarding adjustments to the spark timing value that can bring the engine knock level to, or around, the threshold engine knock level. Additionally, although <FIG> does not depict NOx levels, in at least certain situations, the knock index controller <NUM> can also provide instructions to moderator module <NUM> that can bring the NOx levels to, or around, the threshold target NOx level. As previously discussed, in such a situation, the moderator module <NUM> can evaluate, and select one of, the instructions provided by the NOx feedback controller <NUM> and the knock index controller <NUM>. Further, as also previously discussed, according to certain embodiments, such selection can be based on which of the instructions provide the largest retardation of the combustion event, which can at least assist in facilitating at least one of the NOx and engine knock levels being at or around the associated threshold target value and the other of the NOx and engine knock levels being at, around, or below the associated threshold target value. In the example depicted in <FIG>, the moderator module <NUM> may have selected the information or instructions of the knock index controller <NUM>, which, when implemented, retards the spark timing in a manner that results in the engine knock levels (indicated by operating point P2) being around, or relatively slightly below, the threshold target engine knock level.

Additionally, according to the illustrated example shown in <FIG>, the control strategy can also include attempts to bring the spark timing level or value back to, or around, the target spark timing level or value while maintaining the engine knock level at or around the target knock limit. According to the illustrated embodiment, the increase in spark timing can be associated with an increase in the air-to-fuel ratio (lambda). Thus, with such modifications, as shown by operating point P3 in <FIG>, such adjustments can result in the spark timing returning to the target spark timing value while the engine knock level remains around, or slightly below, the target or threshold knock limit.

While, for at least purposes of illustration, <FIG> and the associated discussion are directed to instances involving adjustments that are at least initially based on engine knock levels, such discussion would apply in a similar manner for controlling NOx levels. For example, such an example could involve replacing the horizontal dashed line depicted in <FIG> that provides an indication relating to engine knock with a similar line that provides an indication of NOx levels. Further, such an example could also involve retarding spark timing to bring the NOx levels around or below the threshold or target NOx level, and subsequently adjusting the air-to-fuel ratio, such as, for example, leaning the air-to-fuel ratio, accordingly to compensate for subsequent changes in spark timing that bring the spark timing level back to, around the target spark timing value while still maintaining the adjusted NOx levels around or below the corresponding threshold or target NOx level.

Referencing <FIG>, generally, combustion advance can be a relatively major factor in attaining higher brake thermal energy (BTE). Additionally, in at least certain situations, higher brake thermal energy (BTE) can be attained at relatively lower NOx levels. Thus, according to certain embodiments, the controller <NUM> can be configured to control the engine system <NUM> in a manner that attains relatively lean air-to-fuel ratios (lambda), such as, for example, NOx levels that allow further combustion advance up to an engine knock limit. Moreover, the controller <NUM> can be adapted to operate the engine system <NUM> to lean out the air-to-fuel ratio to levels that can further combustion advance up to an engine knock limit, as indicated, for example, by at least operating point P3 in <FIG>.

<FIG> includes a graphical representation of changes in NOx levels for two situations, one in which the NOx level was limited ("NOx Limited"), such as, for example, limited up to a certain value (as measured by parts per million (NOx ppm)), and the other in which the engine knock level was limited ("Knock Limited"). <FIG> also includes a depiction of brake thermal energy (BTE) associated with both situations, and more specifically, for the situations in which the depicted NOx levels were limited and situations in which engine knock levels were limited. As shown in <FIG>, for the NOx limited situation, and then the engine knock limited situation, the average spark timing was stepped up, such as, for example, being changed from an average spark timing that was retarded from a base spark timing value (as indicated by <NUM> degrees) by six degrees to an average spark timing value that was advanced by six degrees. Accordingly, in connection with stepping up such increases in the average spark timing value, the air-to-fuel ratio (lambda) was also adjusted in a manner that at least attempted to maintain the limited NOx level and/or the limited engine knock level.

As demonstrated by the data in <FIG>, an increase in average spark timing can be associated with an increase in brake thermal energy (BTE). Moreover, as shown in <FIG>, according to the illustrated example, a change in average spark timing from negative six degrees to positive six degrees relative to a base spark timing is shown as being associated with an approximately <NUM>% increase in the change in the brake thermal energy. Further, as shown, the maximum BTE was attained that at the maximum advanced spark timing and when the engine knock level was limited, rather than when the NOx level was limited.

Accordingly, as derived from the information provided by <FIG>, maximizing combustion advances can maximize BTE. Further, such combustion advance can be maximized by either limiting NOx or engine knock levels. Thus, according to certain embodiments, the controller <NUM> can be structured to drive the combustion event to either the NOx level limit, or to the engine knock limit. Further, in at least certain instances, the controller <NUM> can be configured to drive further advance at the engine knock limit, which can lead to enhanced BTE levels with lower than target NOx levels.

Additionally, a control strategy that employs average spark timing adjustments can also be adapted to address other changes in the engine system <NUM>, such as, for example, changes relating to loss of throttle margin, including, for example, loss of throttle margin at relatively low methane margins. Additionally, the controller <NUM>, including, for example, the spark timing module <NUM> and/or the air-to-fuel module <NUM>, can also be configured to adjust to other operating conditions. For example, according to certain situations, increases in intake manifold temperature (IMT) can result in increases in flame speeds that can increase engine knock and NOx levels. Thus, according to certain embodiments, the controller <NUM> can be electrically coupled to a temperature sensor <NUM> or other sensor that can indicate the temperature of the intake manifold <NUM> (<FIG>) of the engine <NUM>. According to such an embodiment, in response to information indicating an increase in the IMT, such as, for example, the IMT exceeding a threshold value(s) or range(s), the controller <NUM> can be configured to automatically lean out the air-to-fuel ratio.

Additionally, in at least certain situations, decreases in the humidity of the intake gas, such as, for example, decreases in the humidity level of charged air delivered from the turbine 114a to the intake manifold <NUM> and/or engine <NUM>, among other intake gases, can result in increases in flame speeds that can increase engine knock and NOx levels. Thus, according to certain embodiments, the engine system <NUM> can include a sensor that can provide an indication of, or information used to determine, a humidity level(s) of the intake gas. According to such an embodiment, the controller <NUM> can be configured to determine, for example, if the humidity level of the intake gas or charge flow exceeds a threshold value(s) or range(s). If the controller <NUM> determines that the intake gas or charge flow exceeds the threshold value(s) or range(s), the controller <NUM>, such as, for example, the air-to-fuel module <NUM>, can adjust the operation of the fuel injection system <NUM> so as to lean out the air-to-fuel ratio provided in the cylinder of the engine <NUM>.

Similarly, the controller <NUM>, including, for example, the NOx feedback controller <NUM>, can be configured to adjust to detected changes in the BTU characteristics of the fuel. For example, in addition to adapting to changes in the methane number (MN) of the fuel, the controller <NUM> may be structured to adjust to changes detected in BTU in the fuel delivered to the cylinders of the engine <NUM>. Such changes in the BTU of the fuel may be determined in a number of manners, including, for example, via analysis of the combustion event(s) in the cylinder(s) by the controller <NUM>. Further, such changes can relate to, but is not limited to, the addition of diluents, including changes relating to the addition of, or adjustments in the quantity of, carbon dioxide (CO<NUM>) in the fuel, among other diluents. According to certain embodiments, such adjustments in response to changes in the BTU characteristics can include further adjustments in spark timing and/or the air-to-fuel ratio, as previously discussed.

Claim 1:
A system comprising:
a lean-bum spark ignition engine (<NUM>);
an electronic controller (<NUM>) comprising:
a first condition level determining means (<NUM>, <NUM>) for determining a first condition level;
a second condition level determining means (<NUM>, <NUM>) for determining a second condition level;
a first feedback controller (<NUM>, <NUM>) configured to determine a first difference between a first target condition level and the first condition level and to determine, based at least in part on the first difference, a first adjusted spark timing value;
a second feedback controller (<NUM>,<NUM>) configured to determine a second difference between a second target condition level and the second condition level and to determine, based at least in part on the second difference, a second adjusted spark timing value;
a moderator module (<NUM>) configured to adjust a spark timing event in one or more cylinders of an engine based on the first adjusted spark timing value and the second adjusted spark timing value;
the system being characterised in that it further comprises:
a spark-timing controller configured to determine a third difference between a target spark timing value and the moderator adjusted spark timing value after adjustment of the spark timing value to the moderator adjusted spark timing value, and to determine an adjusted air-to-fuel ratio based on the third difference; and
a charge flow controller (<NUM>) adapted to adjust the air-to-fuel mixture and the spark timing based on the moderator adjusted spark timing value and the adjusted air-to-fuel ratio.