Systems and methods for controlling exhaust gas recirculation

Various systems and method for controlling exhaust gas recirculation (EGR) in an internal combustion engine are provided. In one embodiment, a method includes injecting fuel to a subset of cylinders that includes less than all cylinders of a first cylinder group to obtain a target EGR rate. The first cylinder group provides exhaust gas through an exhaust gas recirculation (EGR) passage structure fluidly coupled between the first cylinder group and an intake passage structure. The method further includes injecting fuel to at least one cylinder of a second cylinder group. The second cylinder group provides substantially no exhaust gas through the EGR passage structure.

FIELD

Embodiments of the subject matter disclosed herein relate to exhaust gas recirculation (EGR) systems and methods.

BACKGROUND

Some engines utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce combustion temperatures and regulated emissions. In some examples, a first group of one or more cylinders provides exhaust gas that is directed through an EGR passage coupled between the first group of cylinders and an intake manifold to provide EGR while a second group of one or more cylinders provides substantially no exhaust gas to the EGR passage. In such a configuration, EGR rate is typically controlled through operation of a valve that is located in the EGR passage. The valve position is controlled to vary a mass flow rate of EGR provided to the intake manifold.

BRIEF DESCRIPTION OF THE INVENTION

In embodiments of the invention, under some conditions, exhaust gas recirculation (EGR) composition is controlled in a manner other than by controlling EGR mass flow rate through adjustment/control of an EGR valve. This is because adjusting EGR mass flow rate can be less accurate or can have looser tolerances that result in greater NOx emissions.

Thus, in one embodiment, a method for controlling an engine includes injecting fuel to a subset of cylinders that includes less than all cylinders of a first cylinder group to obtain a target exhaust gas recirculation (EGR) rate. The first cylinder group provides exhaust gas through an EGR passage structure fluidly coupled between the first cylinder group and an intake passage structure. The method further includes injecting fuel to at least one cylinder of a second cylinder group. The second cylinder group provides substantially no exhaust gas through the EGR passage structure.

Operating with some cylinders completing a combustion cycle without combusting is referred to herein as “skip firing.” By skip firing cylinders in the cylinder group that provides EGR while injecting fuel to at least one cylinder of the other cylinder group, EGR is adjusted to meet the target EGR rate while achieving tighter tolerances on NOx and particulate matter (PM) emissions relative to controlling an EGR mass flow rate, for example. Moreover, by controlling EGR through skip firing of the cylinders that provide EGR, any valves or other control elements downstream of those cylinders for controlling the flow of EGR can be eliminated from the engine. In this way, the production cost of the engine is reduced. Further still, preferentially skip firing cylinders that provide EGR over cylinders that provide substantially no EGR facilitates the reduction of EGR to low levels that are favorable under some operating conditions.

DETAILED DESCRIPTION

The present description relates to various embodiments of systems and methods for controlling exhaust gas recirculation (EGR) in an engine having different groups of cylinders that selectively provide EGR. More particularly, the present description relates to preferentially skip firing cylinders that provide EGR over cylinders that provide substantially no exhaust gas to an EGR passage structure in order to reduce EGR under various conditions. Furthermore, in one example, a fuel injection amount of the cylinders that provide EGR is adjusted to vary the EGR rate with a higher granularity from substantially no EGR to a full capability of the cylinders that provide EGR.

In some embodiments, the engine is configured to be positioned in a vehicle, such as a rail vehicle. The above described methods and configurations are particularly advantageous in a rail vehicle due to the sustained periods of low load operation rail vehicles undergo, for example sitting at idle mode during loading and unloading of cargo, idling in the yard, or other idle operation. In one example, “low-load” operation comprises a mode of operation of the engine where a relatively low amount of work is performed by the engine, for example, low-load operation is less than 50% of maximum engine load. Conversely, a “high-load” operation of the engine comprises a mode of operation where a relatively higher amount of work is performed by the engine, for example operation at greater than 50% maximum engine load.

In some embodiments, the system and methods for controlling the EGR rate by skip firing the cylinders that provide EGR is employed to de-rate engine output during some conditions. For example, this approach is particularly applicable to tunnel operation. Specifically, during tunnel operation (referring to a vehicle traveling through a tunnel), the ambient temperature in the tunnel is increased due to the inherent trapping of exhaust gas expelled from the engine in the confines of the tunnel. Thus, the performance of a rail vehicle (e.g., rate at which the rail vehicle travels through the tunnel) can be increased by skip firing one or more cylinders that provide EGR to increase the air/fuel ratio and reduce the need to de-rate the engine. Moreover, combustion temperatures, heat rejected to the tunnel, and the heat load of the EGR cooler is reduced.

FIG. 1schematically shows an embodiment of a vehicle system100(e.g., a locomotive system), herein depicted as a rail vehicle, configured to run on a rail102using a plurality of wheels104. The rail vehicle100includes an engine system106. In other non-limiting embodiments, the engine system106is a stationary engine system, such as in a power-plant application, and in yet other applications, the engine is used in a ship, on-highway vehicle, off-highway vehicle, or other propulsion system.

In one example, the rail vehicle100is a diesel-electric vehicle. For example, the engine system106includes a diesel engine that generates a torque output that is transmitted to a generator108. The generator108produces electrical power that is stored and/or applied for subsequent propagation to a variety of downstream electrical components. For example, the generator108provides electrical power to a plurality of traction motors110. As depicted, the plurality of traction motors110are each connected to one of a plurality of wheels104to provide tractive power to propel the rail vehicle100. One example rail vehicle configuration includes one traction motor per axle (wheel pair). As depicted herein, six traction motors correspond to each of six pairs of wheels of the rail vehicle.

A combustion chamber (i.e., cylinder)112of engine106includes combustion chamber walls114with a piston116positioned therein. The piston116is coupled to a crankshaft118so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. In some embodiments, the engine106is a four-stroke engine in which each of the cylinders fires in a firing order during two revolutions of the crankshaft118. In other embodiments, the engine106is a two-stroke engine in which each of the cylinders fires in a firing order during one revolution of the crankshaft118.

The combustion chamber112receives intake air from an intake passage structure120and exhausts combustion gases to an exhaust passage structure122. The intake passage structure120and the exhaust passage structure122selectively communicate with the combustion chamber112by an intake valve124and an exhaust valve126. In some embodiments, the combustion chamber112includes two or more intake valves and/or two or more exhaust valves.

In this example, the intake valve124and exhaust valve126are controlled by cam actuation systems128and130, respectively. Cam actuation systems128and130each include one or more camshafts and utilizes one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that is operated by a controller132to vary valve operation.

A fuel injector134is shown coupled directly to cylinder112for injecting fuel directly therein. In this manner, fuel injector134provides what is known as direct injection of a fuel into combustion cylinder112. In one example, the fuel is diesel fuel that is combusted in the engine through compression ignition. In other non-limiting embodiments, the fuel is natural gas, and/or gasoline, kerosene, biodiesel, or other petroleum distillates of similar density, that are combusted in the engine through compression ignition (and/or spark ignition).

The controller132at least partially controls operation of the vehicle system100and the engine106. The controller132includes a microprocessor unit (e.g., a processor)136and an electronic storage medium (a.k.a., a computer-readable storage medium)138. For example, the computer-readable storage medium includes one or more of a read-only memory chip, random access memory, etc. The computer readable storage medium138holds instructions that when executed by the microprocessor unit136executes programs for controlling operation of the engine106as well as methods discussed in further detail below with reference toFIGS. 3-5.

The controller132, while overseeing control and management of the vehicle system100, is configured to receive signals from a variety of engine sensors140in order to determine operating parameters and operating conditions, and correspondingly adjust various engine actuators142to control operation of the vehicle system100. For example, the controller132receives sensor signals indicative of air-fuel ratio, engine speed, engine load, engine temperature, ambient temperature, intake manifold temperature, exhaust temperature, intake manifold pressure (boost pressure), exhaust pressure, ambient altitude, intake manifold oxygen concentration, combustion stability, particulate matter concentration, and NOx emissions etc. For example, the controller132adjusts actuators including fuel injectors, intake and exhaust valves, bypass valves, flow valves, etc. In some embodiments, the controller132controls a frequency and/or duration of fuel injection individually for each fuel injector134of the engine106. For example, under some conditions, an amount of fuel injected into cylinders of a first cylinder group is different than an amount of fuel injected into cylinders of a second cylinder group. Furthermore, under some conditions, a number of cylinders in which fuel is injected differs between different cylinder groups.

As another example, one of the sensing devices140includes a global positioning system (GPS) receiver. The controller132determines (e.g., through estimation or calculation) a geographic position (e.g., coordinates) of the vehicle system100using signals from GPS receiver. Geographic features in the path of the vehicle system100, such as features on or around the rail102of the rail vehicle100, is signaled by an operator or calculated. In some implementations, the sensing devices140include a route-feature database. The route-feature database includes information describing different features and regulations that are considered as environmental conditions on a route of the vehicle system100. In one example, designated geographic features and their respective GPS positions are stored in the route-feature database. A distance between the rail vehicle100and any one of the set of designated geographic features is calculated so that the nearest geographic feature and its distance are determined. Non-limiting examples of geographic features that are stored in a set of designated geographic features include a tunnel, a tunnel entrance, a tunnel exit, a geographic region having different emissions restrictions, a steep grade, a city boundary, and a restricted speed boundary. Further, the route-feature database includes stored information about the predefined geographic features, such as length of a tunnel and grade of the tunnel.

In one example, the controller132is operable to determine a tunnel condition based on information received from the GPS receiver and/or route-feature database. For example, a tunnel condition includes operation of the vehicle system within a tunnel. Further, the beginning and end of the tunnel condition are determined in order to accurately adjust operation of the vehicle system. In another example, the controller132is operable to determine a tunnel condition based on ambient temperature and intake manifold oxygen concentration.

As described above,FIG. 1shows only one cylinder of a multi-cylinder engine, however, each cylinder similarly includes its own set of intake/exhaust valves, fuel injector, etc.

FIG. 2schematically shows an embodiment of an engine system200including a plurality of cylinders202. The plurality of cylinders202is organized into a first cylinder group204and a second cylinder group206. Note that “first” and “second” are labels to denote the cylinders of the first and second cylinder groups, respectively. In one example, the engine system200is implemented in a vehicle, such as the vehicle system100shown inFIG. 1.

The first cylinder group204provides exhaust gas that is directed to an intake manifold208of the engine system200. The intake manifold refers to a passage structure or passages that link to cylinder input ports for providing intake air to the cylinders. In the illustrated embodiment, the first cylinder group204provides exhaust gas exclusively to the intake manifold208. In other words, the first cylinder group204is not coupled to an exhaust manifold210, and further is not directly fluidly coupled to an exhaust passage structure212that expels exhaust gas to the atmosphere.

The second cylinder group206is coupled to the exhaust manifold210. Under some conditions, the second cylinder group206provides exhaust gas that is directed through the exhaust passage structure212and expelled to the atmosphere. Under some conditions, the second cylinder group206provides exhaust gas that is directed through a bypass passage structure248to the intake manifold208. In other words, in the illustrated embodiment, the first cylinder group provides exhaust gas merely for EGR and the second cylinder group selectively provides exhaust gas for EGR or to be expelled to the atmosphere. In some embodiments, the first cylinder group is exclusive of the second cylinder group. “Exclusive” means that no cylinder of the first cylinder group is included in the second cylinder group. In the illustrated embodiment, the engine200is a V-12 engine having twelve cylinders. In other examples, the engine is a V-6, V-8, V-10, V-16, I-4, I-6, I-8, opposed 4, or another engine type. It will be appreciated that each of the cylinder groups includes a suitable number of cylinders. Furthermore, the engine system includes a suitable number of cylinder groups.

The intake manifold208couples to the first cylinder group204and the second cylinder group206. An intake passage structure214is coupled to the intake manifold208to supply fresh air to the intake manifold208for combustion. A staged or series turbocharger setup including a first turbocharger216and a second turbocharger224is positioned in the intake passage structure214to compress intake air. The first turbocharger216includes a first compressor218positioned in the intake passage structure214and a first turbine220positioned in the exhaust passage structure212. The first turbine220is driven at least partially by exhaust gas provided by the second cylinder group206through the exhaust manifold210. A first liquid-cooled charge air cooler222is positioned in the intake passage structure214downstream of the first compressor218. The second turbocharger224includes a second compressor226positioned in the intake passage structure214downstream of the first cooler222and a second turbine228positioned in the exhaust passage structure212upstream of the first turbine220. The second turbine228is driven at least partially by exhaust gas provided by the second cylinder group206through the exhaust manifold210. A second liquid-cooled charge air cooler230is positioned in the intake passage structure214downstream of the second compressor226.

In the illustrated implementation, the engine system200does not include a throttle valve positioned in the intake passage structure214. However, in some implementations, the intake passage structure120includes a throttle valve positioned downstream of the second compressor226.

Each of the plurality of cylinders202includes a fuel injector232operable to inject fuel into that cylinder, at least one intake port234that is operable to receive combustion air from the intake manifold208, and at least one exhaust port236that is operable to exhaust gas to an exhaust manifold. An exhaust manifold (a.k.a., an EGR manifold)238is coupled to the first cylinder group204to receive exhaust gas from the first cylinder group. In the illustrated embodiment, the EGR manifold238is not coupled to the second cylinder group206. An EGR passage structure240is coupled between the EGR manifold238and the intake passage structure214. Under some conditions, exhaust gas provided by the first cylinder group204flows through the EGR passage structure240into the intake passage structure214, where it mixes with fresh intake air and the mixture is provided to the plurality of cylinders202through the intake manifold208for combustion. In the illustrated embodiment, the EGR passage structure240is not coupled to the exhaust manifold210. A liquid-cooled EGR cooler252is positioned in the EGR passage structure240to cool exhaust gas before the exhaust gas is circulated to the intake manifold208.

In the illustrated embodiment, the EGR passage structure240does not include a control device operable to control flow of exhaust gas to the intake passage structure. In other words, there are no valves or other control elements positioned downstream of the first cylinder group for controlling the flow of EGR. However, it will be appreciated that in some embodiments, the EGR passage structure includes one or more valves for controlling the flow of exhaust gas provided by the first cylinder group.

The exhaust manifold210is coupled to the second cylinder group206to receive exhaust gas from the second cylinder group. In the illustrated embodiment, the exhaust manifold210is not coupled to the first cylinder group204. Under some conditions, exhaust gas provided by the second cylinder group206travels from the exhaust manifold210, through the second turbine228of the second turbocharger224, through the first turbine220of the first turbocharger216to be expelled from the exhaust passage structure212into the atmosphere. Under some conditions, the exhaust gas bypasses the second turbine228through an exhaust bypass passage structure242. An exhaust bypass valve244is positioned in the exhaust bypass passage structure242. The exhaust bypass valve244is operable to control flow of exhaust gas through the exhaust bypass passage structure242. For example, the bypass valve244is adjusted to bypass the second turbine228to lower boost pressure under some conditions.

An exhaust gas treatment system246is provided in the exhaust passage structure212, downstream of the first turbine220. The exhaust gas treatment system246treats exhaust gas before it is released to the atmosphere. For example, the exhaust gas treatment system includes a selective catalytic reduction (SCR) system, a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), various other emission control devices, or combinations thereof.

A bypass passage structure248is coupled between the exhaust passage structure212and the intake passage structure214. More particularly, the bypass passage structure248is positioned between a point in the exhaust passage structure212upstream of the second turbine228and downstream of the exhaust manifold210and a point in the intake passage structure214downstream of the second compressor226and upstream of the second cooler230. Under some conditions, exhaust gas provided by the second cylinder group flows from the exhaust passage structure212, through the bypass passage structure248, to the intake passage structure214to provide EGR to the plurality of cylinders202. Furthermore, under some conditions, intake air flows from the intake passage structure214, through the bypass passage structure248, and to the exhaust passage structure212to accelerate the turbines of the turbochargers. A bypass valve250is positioned in the bypass passage structure to control flow of exhaust gas or intake air through the bypass passage structure248.

A controller254includes a processor256and computer-readable medium258having non-transient instructions that when executed by the processor256execute control routines to control the engine200and more particularly control EGR during various operating conditions. The controller254receives signals from a variety of engine sensors260in order to determine operating parameters and operating conditions, and correspondingly adjusts various engine actuators262.

In one embodiment, the controller254is operable to determine a target EGR rate. In one example, the target EGR rate is determined based on one or more of engine load, engine speed, combustion stability, particulate matter concentration, intake manifold oxygen concentration, or NOx emissions. Further, the controller254is operable to control injection of fuel to a subset of cylinders that includes less than all cylinders of the first cylinder group to obtain the target EGR rate, and to control injection of fuel to each cylinder of the second cylinder group. In other words, the controller is configured to control skip firing of the cylinder group that provides exhaust gas to the EGR passage structure and to control fueling of each cylinder of the other cylinder group that does not provide exhaust gas to the EGR passage structure. In some embodiments, the controller controls fuel injection such that fuel is injected to only the subset of cylinders, and substantially no fuel is injected into members of the first cylinder group that are not in the subset. By skip firing or shutting off the fuel to one or more cylinders that comprise the subset of the first cylinder group, the amount of exhaust produced by the non-firing cylinders is reduced to zero, thus reducing the total amount of exhaust gas recirculated to the intake manifold.

For example, during skip-fire operation, in one combustion cycle, at least one but fewer than all the cylinders of the first cylinder group are fired while every cylinder from the second cylinder group is fired. In this manner, across multiple engine cycles, the cylinders of the second cylinder group fires more often than the cylinders of first cylinder group. In some embodiments, the subset is varied so that each cylinder of the first cylinder group fires at some point over multiple combustion cycles. Under some conditions, all cylinders of the first cylinder group are skip-fired in order to reduce the EGR provided by the first cylinder group to substantially zero. In some embodiments, different cylinders are skip fired or partially fuelled during different combustion cycles. For example, a cylinder designated for skip firing may be rotated around after each combustion cycle, or some number of combustion cycles.

Furthermore, the amount of EGR could be further reduced if the fueling were shut off every other cycle. Even finer adjustment of the EGR rate may be attained by skip firing the donor cylinders every 3rd or 4th cycles, etc. In one example, the controller254is operable to control injection of fuel to the subset of cylinders of the first cylinder group during a first combustion cycle and to control injection of fuel to each cylinder of the first cylinder group during a second combustion cycle to obtain the target EGR rate. In one example, at least one combustion cycle separates the first combustion cycle and the second engine cycle. In other words, the controller varies the number of combustion cycles between skip fire events in order to obtain the target EGR rate. Such an approach provides more granular adjustment than controlling EGR flow rate through an EGR valve.

In one embodiment, the controller254is operable to adjust a fuel injection amount to at least one cylinder of the subset of cylinders of the first cylinder group to obtain the target EGR rate. For example, if less fuel is burned in the active cylinders that are not skip fired in the first cylinder group, the amount of exhaust gasses produced by the first cylinder group are reduced, providing an overall reduction in EGR rate. The combination of skip firing and adjusting fuel injection to the active cylinders of the first cylinder group facilitate variable EGR rate control with very high granularity relative to controlling EGR through EGR flow control.

Moreover, aside from the challenging controls and the adverse environment in which an EGR valve operates, a further complication of the EGR flow control approach is that it shifts an operating point of the turbochargers towards a choke condition. In other words, if all of the exhaust of the donating cylinders is combined with the exhaust of the non donating cylinders, the turbocharger would need to be approximately 50% larger in order to handle the combined flow. As such, the turbocharger would be sub-optimized under various operating conditions in order to accommodate the large range of exhaust flow. By varying the EGR rate with skip fire and/or reduced fueling of the donor cylinders, the exhaust flow to the turbocharger could be held relatively constant, thus enabling optimized (or at least improved) performance of the turbochargers over a very broad operating range.

In one embodiment, the controller254is operable to adjust a fuel injection amount to at least one cylinder of the second cylinder group dependent upon the first cylinder fuel injection adjustment to attain or maintain a target torque output provided by the first cylinder group and the second cylinder group. In some embodiments, the fuel injection amount of the second cylinder group is adjusted to attain or maintain an operating parameter other than torque output.

Furthermore, in another embodiment, the controller254is additionally or alternatively operable responsive to a tunnel condition. More specifically, the controller is configured, during a tunnel condition, to determine a second EGR rate that has a higher oxygen concentration than the target EGR rate, and to control injection of fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the second EGR rate. Furthermore, in another embodiment, the controller254is additionally or alternatively operable, in response to the tunnel condition, to determine a target power level, and to control injection of fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the target power level. By skip firing one or more cylinders that provide EGR, overall power output of the engine can be reduced, with the added benefit of increasing the combustion air/fuel ratio and reducing the heat rejected to the EGR cooler.

Furthermore, in another embodiment, the controller254is additionally or alternatively operable responsive to an ambient temperature being greater than a temperature threshold value or an ambient air pressure being less than a pressure threshold value. More specifically, during such a condition, the controller is configured to determine a second EGR rate that has a higher oxygen concentration than the target EGR rate, and to control injection of fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the second EGR rate. By skip firing more cylinders that provide EGR during adverse ambient conditions (e.g., high temperature or low density air), the heat load on the EGR cooler is reduced.

FIG. 3schematically shows another embodiment of an engine system300. Components of the engine system300that are substantially the same as those of the engine system200are identified in the same way and are described no further. However, it will be noted that components identified in the same way in different embodiments of the present disclosure can be at least partly different.

The engine system300includes additional valves in the EGR passage structure that allow the first cylinder group and/or the second cylinder group to selectively provide exhaust gas to the intake manifold and/or the exhaust manifold. In other words, in the illustrated embodiment, the first cylinder group can provide exhaust gas for EGR and/or to the exhaust passage structure. In particular, the EGR passage structure340is selectively fluidly coupled to the exhaust manifold310. An EGR bypass valve364is positioned in the EGR passage structure340. The EGR bypass valve364is operable to control the flow of exhaust gas from the first cylinder group304through the EGR passage structure340to the exhaust manifold310and/or the exhaust passage structure312.

An EGR flow valve366is positioned in the EGR passage structure340between EGR manifold338and the EGR cooler352. The EGR flow valve366is operable to control EGR flow through the EGR passage structure to the EGR cooler352. The EGR bypass valve364and the EGR flow valve366are cooperatively controlled by the controller354to direct exhaust gas flow from the first cylinder group304based on operating conditions.

In the illustrated embodiment, the bypass passage structure348is positioned downstream of the second cooler330. As such, hot exhaust gas is passed through the bypass passage to the intake passage without being cooled by the second cooler. By not cooling the exhaust gas with the second cooler, the exhaust gas heats the cylinder more quickly relative to EGR that is cooled by the second cooler. Although it will be appreciated that in some embodiments the bypass passage structure is positioned upstream of the second cooler.

In one embodiment, the controller354is operable to close the EGR bypass valve364, open the EGR flow valve366, control fuel injection to a subset of cylinders that includes less than all cylinder of the first cylinder group to obtain a target EGR rate, and control fuel injection to each cylinder of the second cylinder group. In other words, the controller controls skip firing of the cylinder group that provides exhaust gas to the EGR passage structure and control fueling of cylinders of the other cylinder group that does not provide exhaust gas to the EGR passage structure. By skip firing or shutting off the fuel to one or more cylinders that comprise the subset of the first cylinder group, the amount of exhaust produced by the non firing cylinders is reduced to zero, thus reducing the total amount of exhaust gas recirculated to the intake manifold.

Furthermore, in another embodiment, the controller354is operable to adjust an opening position of the EGR bypass valve and an opening position of the EGR flow valve to control a flow of exhaust gas provided to the EGR passage to obtain the target EGR rate.

FIG. 4shows a flow chart of an embodiment of a method400for controlling EGR in an engine. In one embodiment, the method400is executed by the controller142inFIG. 1or the controller254inFIG. 2. At402, the method400includes determining operating conditions. For example, operating conditions may be determined based on operating parameters indicative of sensor signals received from sensors coupled to the engine, such as intake pressure, exhaust pressure, engine temperature, ambient temperature, air-fuel ratio, engine speed, engine load, exhaust temperature, exhaust pressure, ambient pressure, ambient altitude, etc.

At404, the method400includes determining a target EGR rate. In one embodiment, the target EGR rate is determined based on one or more of engine load, engine speed, combustion stability, particulate matter concentration, intake manifold oxygen concentration, or NOx emissions.

At406, the method400includes injecting fuel to a subset of cylinders that includes less than all cylinders of a first cylinder group to obtain the target EGR rate. In one embodiment, the method includes injection fuel to only cylinders in the subset of the first cylinder group and no fuel is injected to members of the first cylinder group that are not in the subset. In one embodiment, the first cylinder group provides exhaust gas through an EGR passage fluidly coupled between the first cylinder group and an intake passage. For example, the subset of cylinders receiving fuel is increased as the target EGR rate increases and the subset of cylinders receiving fuel is decreased as the target EGR decreases. For example, injecting fuel to the subset of cylinders of the first cylinder group can be performed every combustion cycle, every other combustion cycle, every 3rdor 4thcombustion cycle, etc. over a designated number of combustion cycles to obtain the target EGR rate.

At408, the method400includes injecting fuel to at least one cylinder of a second cylinder group. The second cylinder group provides substantially no exhaust gas through the EGR passage. For example, the second cylinder group provides exhaust to an exhaust passage that fluidly couples to the atmosphere instead of providing exhaust gas to the EGR passage. It will be appreciated that a number of cylinders of the first cylinder group are fueled/fired less often than a number of cylinders of the second cylinder group over a designated number of combustion cycles. In one embodiment, the method400includes injection fuel to each cylinder of the second cylinder group.

At410, the method400includes adjusting a fuel injection amount to at least one cylinder of the subset of cylinders of the first cylinder group to obtain the target EGR rate.

At412, the method400includes adjusting a fuel injection amount to at least one cylinder of the second cylinder group dependent upon the first cylinder group fuel injection adjustment to attain or maintain a target torque output provided by the first cylinder group and the second cylinder group. For example, if the fuel injection amount of one or more cylinders of the subset of the first cylinder group is decreased to obtain the target EGR rate, then a fuel injection amount of one or more cylinder of the second cylinder group is increased by a corresponding amount.

By skip firing cylinders that provide EGR while fueling cylinders that provide substantially no EGR, more accurate and less complicated EGR control is achieved relative to an approach that employs EGR valves in the EGR passage. Accordingly, such valve that would otherwise be necessary to direct some of the EGR gasses into the non-EGR gas stream can be potentially eliminated from the engine. Moreover, by eliminating valves from the EGR passage, the turbocharger can be suitably matched to an exhaust flow of a fixed number of cylinders, thus minimizing a map width of the turbocharger and correspondingly more efficient operation over a broader range of operating conditions. In other words, by varying the EGR rate with skip fire or reduced fueling of the cylinders that provide EGR, the exhaust flow to the turbocharger could be held relatively constant, thus enabling optimized performance of the turbochargers over a very broad operating range.

FIG. 5shows a flow chart of an embodiment of a method500for controlling EGR in an engine during a tunnel condition. In one embodiment, the method500is executed by the controller132inFIG. 1or the controller254inFIG. 2. At502, the method500includes determining operating conditions. The method500is executed alone or in combination with the method300shown inFIG. 3.

At504, the method500includes determining whether there is a tunnel condition. For example, the tunnel condition includes a locomotive or other vehicle entering or operating in a tunnel. In one embodiment, a tunnel condition is determined based on GPS information and/or route-feature information. In another embodiment, the tunnel condition is determined based on ambient temperature and intake manifold oxygen concentration. If it is determined that there is a tunnel condition, then the method500moves to506. Otherwise, the method500returns to other operations.

At506, the method500includes determining a second EGR rate that has a higher oxygen concentration than the target EGR rate. For example, the target EGR rate is determined based on operation outside of the tunnel. The second EGR rate has a higher oxygen concentration than the target EGR rate due to the reduced fresh air inducted during operation in the tunnel due to expelled exhaust gas being trapped in the tunnel. Moreover, the second EGR rate is increased relative to the target EGR rate due to the reduced heat rejection capability of the locomotive and resultant increased fluid temperatures (e.g., oil, water, air) that occurred during tunnel operation.

At508, the method500includes injecting fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the second EGR rate. In one embodiment, the method includes injection fuel to only cylinders in the subset of the first cylinder group and no fuel is injected to members of the first cylinder group that are not in the subset. In other words, the number of cylinders in the subset are decreased that are fueled is decreased in order to further reduce the EGR and increase the amount of intake air that is provided to the cylinder to achieve the second EGR rate. In one embodiment, all cylinders of the first cylinder group are skip fired to reduce the EGR rate to the second EGR rate.

At510, the method500includes determining a target power level output by the engine. For example, the engine is de-rated to obtain the target power level. In one example, the target power level is determined based on one or more of engine coolant temperature, oil temperature, combustion stability, air/fuel ratio, etc.

At512, the method500includes injecting fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the target power level.

At514, the method500includes injecting fuel to at least one cylinder of the second cylinder group. In one embodiment, the method includes injecting fuel to each cylinder of the second cylinder group.

By skip firing the cylinders that provide EGR to control the EGR rate and de-rate the engine, the performance of the vehicle (e.g., a rate at which the vehicle travels thru the tunnel) can be increased. Moreover, heat rejected to the tunnel is reduced by reducing the heat load of the EGR cooling system, as well as lowering the exhaust temperature due to decreased EGR and/or increased air/fuel ratio.

FIG. 6shows a flow chart of an embodiment of a method600for controlling EGR in an engine during various temperature or pressure conditions. In one embodiment, the method600is executed by the controller132inFIG. 1or the controller254inFIG. 2. At602, the method600includes determining operating conditions. The method600is executed alone or in combination with the method300shown inFIG. 3.

At604, the method600includes determining whether a temperature is greater than a temperature threshold value. For example, the temperature may be an ambient temperature and the temperature threshold value ranges from 25-50° C. In another example, the temperature is an engine coolant temperature and the temperature threshold value ranges from 100-120° C. If it is determined that the temperature is greater than the temperature threshold value, then the method600moves to608. Otherwise the method600moves to606.

At606, the method600includes determining whether a pressure is less than a pressure threshold value. For example, the pressure may be an ambient pressure. If it is determined that the pressure is less than the pressure threshold value, then the method600moves to608. Otherwise the method600returns to other operations.

At608, the method600includes determining a second EGR rate that has a higher oxygen concentration than the target EGR rate. For example, the target EGR rate is determined based on operation at lower temperatures or higher pressures.

At610, the method600includes injecting fuel to less than all cylinders of the subset of cylinders of the first cylinder group to obtain the second EGR rate.

At612, the method600includes injecting fuel to at least one cylinder of the second cylinder group. In one embodiment, the method includes injecting fuel to each cylinder of the second cylinder group.

By skip firing more cylinders that provide EGR during adverse ambient environmental conditions (e.g., high temperature or low density air), heat load on the EGR cooler is reduced. In this way, performance of the engine is increased.

In another embodiment, a method includes during a first condition, injecting fuel to each cylinder of a first cylinder group. The first cylinder group provides exhaust gas through an EGR passage structure fluidly coupled between the first cylinder group and an intake passage structure. The method further includes injecting fuel to each cylinder of a second cylinder group. The second cylinder group provides substantially no exhaust gas through the EGR passage structure. For example, the second cylinder group provides exhaust gas to the atmosphere through an exhaust passage structure. As another example, the second cylinder group may provide exhaust gas to the intake passage structure through a turbocharger bypass instead of through the EGR passage, under some conditions. The method further includes adjusting a fuel injection amount to at least one cylinder of the first cylinder group to obtain a first EGR rate. The method further includes during a second condition, injecting fuel to a subset of cylinders that includes less than all cylinders of the first cylinder group, injecting fuel to each cylinder of the second cylinder group, and adjusting a fuel injection amount to at least one cylinder of the subset of cylinders of the first cylinder group to obtain a second EGR rate that has a higher oxygen concentration than the first EGR rate.

In one example, the first condition includes an engine speed being greater than a speed threshold value and the second condition includes at least one of a tunnel condition, an ambient temperature being greater than a temperature threshold value, or an ambient air pressure being less than a pressure threshold value. Furthermore, the method includes during the second condition, adjusting a fuel injection amount to at least one cylinder of the second cylinder group dependent upon the first cylinder fuel injection adjustment to attain or maintain a target torque output provided by the first cylinder group and the second cylinder group.

Another embodiment relates to a method, e.g., a method for controlling an engine. The method comprises skip firing a first cylinder group, and combusting fuel in at least one cylinder of a second cylinder group. The first cylinder group provides exhaust gas through an EGR passage structure fluidly coupled between the first cylinder group and an intake passage structure. The second cylinder group provides substantially no exhaust gas through the EGR passage structure. The first cylinder group is exclusive of the second cylinder group, that is, none of the cylinders of the first group are also cylinders of the second group. The step of skip firing comprises, in a first combustion cycle, exclusively combusting fuel in a first subset of the first cylinder group that includes less than all cylinders of the first cylinder group. “Exclusively” combusting means that in a given combustion cycle, fuel is combusted in a given subset of the first cylinder group but not combusted in the cylinders of the first cylinder group that are not within the given subset. The step of skip firing further comprises, in a successive, second combustion cycle, exclusively combusting fuel in a second subset of the first cylinder group that includes less than all the cylinders of the first cylinder group. The second subset is at least partially different than the first subset, that is, at least one cylinder of the second subset is not also part of the first subset; in embodiments, the first subset is exclusive of the second subset, meaning no cylinders of the first subset are also part of the second subset. In further successive combustion cycles, the first and second subsets are alternately exclusively combusted, possibly sequentially with other, additional subsets of the first cylinder group (that are at least partially different then the first and second subsets), and possibly alternating with combustion cycles where fuel is combusted in all the cylinders of the first cylinder group. In other embodiments, the method further comprises, for a given subset of the first cylinder group that is being exclusively combusted in a given combustion cycle, adjusting a fuel injection amount to at least one cylinder of the given subset to obtain a target EGR rate.