Patent Description:
Exhaust aftertreatment systems fluidly couple to internal combustion engines to purify exhaust gases generated as byproducts of combustion. Byproducts of combustion may include unburned hydrocarbons, carbon monoxide, nitrides of oxide (NOx), and particulate matter. In general, Exhaust aftertreatment systems may include oxidation catalysts, reduction catalysts, selective catalytic reduction catalysts and particulate filters. When employed on heavy-duty diesel engines or other lean-burning configurations, an exhaust aftertreatment system may include a diesel oxidation catalyst (DOC) to oxidize unburned fuel and carbon monoxide, a diesel particulate filter (DPF) for control of particulate matter (PM), one or more selective catalytic reduction (SCR) systems for NOx reduction, and/or an ammonia oxidation catalyst (AMOX) to eliminate or minimize ammonia slip. Operation of the internal combustion engine and the exhaust aftertreatment system may be monitored by one or more sensing devices that are disposed in the exhaust gas feedstream. Operation may also be determined employing simulation models that dynamically execute during operation.

SCR catalysts may employ reductants for reducing NOx molecules to elemental nitrogen. One reductant is urea, which may be transformed into ammonia (NH3) in an exhaust system. The reductant may be injected into the exhaust gas feedstream upstream of one or multiple SCR catalysts and may be stored on a surface or otherwise captured for use in reducing NOx molecules to elemental nitrogen and water.

Performance of known SCR catalysts is dependent upon temperature, with increased performance being related to increased exhaust gas temperatures.

There is a need to provide a hardware architecture implementation and method to improve heavy-duty diesel NOx emissions in a manner that enables flexibility with existing exhaust aftertreatment hardware with added functionality and independent operation.

Related technologies are shown in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

An exhaust aftertreatment system for a compression-ignition internal combustion engine is described. The exhaust aftertreatment system comprises a base exhaust aftertreatment system and a modular exhaust subsystem for purifying an exhaust gas feedstream of the compression-ignition internal combustion engine upstream of the base exhaust aftertreatment system. The modular exhaust subsystem includes a selective catalytic reduction device (SCR) catalyst, and a first exhaust gas sensor and a first temperature sensor that are arranged to monitor the SCR catalyst. A reductant delivery system is arranged to inject a reductant into the exhaust gas feedstream upstream of the SCR catalyst. A controller is operatively connected to the reductant delivery system and in communication with the first exhaust gas sensor and the first temperature sensor. The controller is further in communication with a second exhaust gas sensor and a second temperature sensor that are arranged to monitor the base exhaust aftertreatment system. The controller includes an instruction set that is executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst based upon inputs from the first and second exhaust gas sensors and the first and second temperature sensors.

The disclosure includes an engine-out exhaust gas sensor arranged to monitor the exhaust gas feedstream upstream of the SCR catalyst. The controller is further in communication with an engine-out exhaust gas sensor. The controller includes instruction set is executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst based upon inputs from the engine-out exhaust gas sensor, the first and second exhaust gas sensors, and the first and second temperature sensors.

The disclosure includes the instruction set being executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst to achieve a target reductant/NOx ratio upstream of the base exhaust aftertreatment system.

Another aspect of the disclosure includes the instruction set being executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst to achieve a target ammonia storage level on the SCR catalyst.

Another aspect of the disclosure includes the first exhaust gas sensor being a NOx sensor.

Another aspect of the disclosure includes the first exhaust gas sensor being a wide range air/fuel ratio sensor.

Another aspect of the disclosure includes the reductant delivery system being arranged to inject urea into the exhaust gas feedstream upstream of the SCR catalyst.

Another aspect of the disclosure includes the reductant delivery system being arranged to inject gaseous ammonia into the exhaust gas feedstream upstream of the SCR catalyst.

Another aspect of the disclosure includes the modular exhaust subsystem being arranged in an underhood location.

Another aspect of the disclosure includes the modular exhaust subsystem being arranged in an underbody location.

Another aspect of the disclosure includes a controllable heating element being arranged in the exhaust gas feedstream upstream of the SCR catalyst.

Another aspect of the disclosure includes a heating device being arranged to transfer heat to the exhaust gas feedstream upstream of the SCR catalyst.

Another aspect of the disclosure includes an oxidation catalyst being arranged upstream of the SCR catalyst.

The disclosure also relates to an exhaust aftertreatment system for an internal combustion engine. The exhaust aftertreatment system comprises a base exhaust aftertreatment system and a modular exhaust subsystem. The modular exhaust subsystem comprises a selective catalytic reduction (SCR) catalyst, a first exhaust gas sensor and a first temperature sensor arranged to monitor the SCR catalyst, a reductant delivery system arranged to inject a reductant into an exhaust gas feedstream upstream of the SCR catalyst, and a controller. The controller is operatively connected to the reductant delivery system and in communication with the first exhaust gas sensor and the first temperature sensor. The modular exhaust subsystem has a physical modularity and a control modularity in relation to a base exhaust aftertreatment system. The base exhaust aftertreatment system includes an exhaust aftertreatment device, an engine-out exhaust gas sensor, and a second exhaust gas sensor and a second temperature sensor that are arranged to monitor the base exhaust aftertreatment system. The controller is in communication with the second exhaust gas sensor, the second temperature sensor and the engine-out exhaust gas sensor.

The physical modularity of the modular exhaust subsystem includes the modular exhaust subsystem being configured to be fluidly coupled between the internal combustion engine and the base exhaust aftertreatment system. The control modularity of the modular exhaust subsystem includes the controller of the modular exhaust subsystem having an instruction set that is executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst based upon inputs from the first and second exhaust gas sensors, the engine-out exhaust gas sensor, and the first and second temperature sensors.

The disclosure includes instruction set being executable to control the reductant delivery system to inject the reductant into the exhaust gas feedstream upstream of the SCR catalyst to achieve a target reductant/NOx ratio upstream of the base exhaust aftertreatment system.

Another aspect of the disclosure includes the exhaust subsystem being arranged in an underhood location.

Another aspect of the disclosure includes the first exhaust gas sensor being arranged to monitor the exhaust gas feedstream downstream of the SCR catalyst, and the first temperature sensor being arranged to monitor the exhaust gas feedstream upstream of the SCR catalyst.

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:.

The appended drawings are not necessarily to scale and may present a simplified representation of various preferred features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes. Details associated with such features will be determined in part by the particular intended application and use environment.

Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the terms "system" and "subsystem" may refer to one of or a combination of mechanical and electrical devices, actuators, sensors, controllers, application-specific integrated circuits (ASIC), combinatorial logic circuits, software, firmware, and/or other components that are arranged to provide the described functionality.

As employed herein, the term "upstream" and related terms refer to elements that are towards an origination of a flow stream relative to an indicated location, and the term "downstream" and related terms refer to elements that are away from an origination of a flow stream relative to an indicated location.

The term 'model' refers to a processor-based or processor-executable code and associated calibration that simulates a physical existence of a device or a physical process.

The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order but may only distinguish between multiple instances of an act or structure.

Referring to the drawings, wherein like reference numerals correspond to like or similar components throughout the several Figures, <FIG> and <FIG>, consistent with embodiments disclosed herein, schematically illustrate elements of an embodiment of an exhaust aftertreatment system <NUM> for purifying the exhaust gas feedstream <NUM> of an internal combustion engine <NUM>, wherein the internal combustion engine <NUM> is controlled to operate primarily in a lean-burn air/fuel ratio environment. One example of the internal combustion engine <NUM> is a multi-cylinder compression-ignition internal combustion engine that is classified as a heavy-duty (HD) engine. In one embodiment, the internal combustion engine <NUM> is disposed on a vehicle. The vehicle may include, but not be limited to a mobile platform in the form of a heavy-duty commercial vehicle, an industrial vehicle, an agricultural vehicle, a watercraft, or a train. Alternatively, the internal combustion engine <NUM> may be arranged as a stationary device, such as for powering an electric power generator.

The exhaust gas feedstream <NUM> generated by the internal combustion engine <NUM> contains byproducts of combustion, including unburned hydrocarbons, carbon monoxide, nitrides of oxide (NOx), particulate matter, etc. The exhaust gas feedstream <NUM> is monitored by an engine-out exhaust gas sensor <NUM>, which may be a NOx sensor, a wide-range air/fuel ratio sensor, or another sensor that monitors one or constituents of the exhaust gas feedstream <NUM> for purposes of monitoring and/or controlling operation of the engine <NUM>.

Engine control includes controlling various engine operating parameters, including controlling engine control states to minimize various exhaust gas constituents through chemical reaction processes that include, by way of non-limiting examples, oxidation, reduction, filtering, and selective reduction. Other engine control states include controlling operating parameters to warm up the engine <NUM> and control heat transfer to various elements of the base exhaust aftertreatment system <NUM> to effect efficacious operation thereof. Heat transfer to the elements of the base exhaust aftertreatment system <NUM> may be employed for warmup and catalyst light-off, regeneration of a particulate filter, etc..

Referring again to <FIG>, the exhaust aftertreatment system <NUM> includes a modular exhaust subsystem <NUM> that is arranged upstream of an embodiment of a base exhaust aftertreatment system <NUM>. The base exhaust aftertreatment system <NUM> is also referred to herein as a second exhaust aftertreatment system <NUM> and is described with reference to <FIG>. The base exhaust aftertreatment system <NUM> is configured to purify the exhaust gas feedstream <NUM> of the internal combustion engine <NUM> to achieve a first tailpipe emissions target in-use. The modular exhaust subsystem <NUM> and the base exhaust aftertreatment system <NUM> are configured to purify the exhaust gas feedstream <NUM> to achieve a second tailpipe emissions target in-use, wherein the second tailpipe emissions target is less than the first tailpipe emissions target that is achievable with the base exhaust aftertreatment system <NUM> alone. Selected results related to emissions performance are graphically illustrated with reference to <FIG>, <FIG>. The tailpipe emissions targets may in the form of regulatory emissions targets that are imposed by the US Environmental Protection Agency, the California Air Resources Board, the European Union, or other regulatory bodies. The tailpipe emissions targets may instead be in the form of in-house or user emissions targets, such as may be imposed by a private fleet owner.

The modular exhaust subsystem <NUM> is a stand-alone modular system configured to be inserted between the engine <NUM> and the base exhaust aftertreatment system <NUM> either during engine/vehicle assembly, or as a retrofit device on an existing vehicle system. The modular exhaust subsystem <NUM> may be placed in an engine compartment in an underhood location, and thus may be closely coupled to the engine <NUM>. The modular exhaust subsystem <NUM> may be fluidly coupled to an exhaust manifold of the engine <NUM>, or to a fluid outlet of a turbocharger or supercharger of the engine <NUM>. Alternatively, the modular exhaust subsystem <NUM> may be located underbody. As employed herein, the term "modular" and related terms that are employed to describe the modular exhaust subsystem <NUM> refer to exhaust aftertreatment components, actuators, sensors, control devices, etc., that are arranged to operate independently to achieve a specific result with minimal or no external dependencies or interactions from other onvehicle systems. The specific result being achieved by one embodiment of the modular exhaust subsystem <NUM> is the reduction of NOx constituents in the exhaust gas feedstream <NUM> upstream of the base exhaust aftertreatment system <NUM>. Furthermore, the presence (or absence) of the modular exhaust subsystem <NUM> is transparent to control and operation of the engine <NUM> and the base exhaust aftertreatment system <NUM>. As such, the operation of the modular exhaust subsystem <NUM> and its effect upon the exhaust gas constituents in the exhaust gas feedstream <NUM> does not affect the control, monitoring, or diagnostics of the engine <NUM> or the base exhaust aftertreatment system <NUM>.

The modular exhaust subsystem <NUM> includes, in one embodiment, a first selective catalytic reduction (SCR) catalyst <NUM>, a first reductant delivery system <NUM> that is arranged to inject, via a first reductant injector <NUM>, a reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM>, a first exhaust gas sensor <NUM> and a first temperature sensor <NUM> that are arranged to monitor the first SCR catalyst <NUM>, and a subsystem controller <NUM>. In one embodiment, a first heating device <NUM> is arranged to transfer heat to the exhaust gas feedstream upstream of the first SCR catalyst <NUM>. In one embodiment, the first heating device <NUM> is a controllable heating element that is arranged in the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM>. The first heating device <NUM> may be an electrically-powered resistive heater or heating element, a burner, or another heater, to inject heat energy into the exhaust gas flow and the injected reductant. In one embodiment, a first oxidation catalyst <NUM> is arranged upstream of the first SCR catalyst <NUM>. The physical modularity of the modular exhaust subsystem <NUM> is depicted by mechanical interfaces in the form of optional flanges <NUM> for connecting the modular exhaust subsystem <NUM> into the exhaust gas feedstream <NUM> between the engine <NUM> and the base exhaust aftertreatment system <NUM>, such as may be helpful in an upfit or a retrofit arrangement. It is appreciated that flanges <NUM> may not be necessary when the modular exhaust subsystem <NUM> is incorporated into a new build. The control modularity is achieved by use of the subsystem controller <NUM> to control the first reductant delivery system <NUM>. The subsystem controller <NUM> interfaces and communicates with other controllers e.g., a second controller <NUM> and an engine controller, via a communication link <NUM> and a communication bus <NUM>. In one embodiment, an optional communication link connector <NUM> links the communication link <NUM> to the communication bus <NUM>.

In one embodiment, the first SCR catalyst <NUM> is a catalytic device that employs a reductant to reduce NOx molecules to form elemental nitrogen (N2) and other inert gases. In one embodiment, the reductant is urea, which can be converted to ammonia (NH3) that is stored on the substrate of the first SCR catalyst <NUM>. Alternatively, the reductant may be gaseous ammonia. The first SCR catalyst <NUM> includes a ceramic or metallic substrate having flow channels that have been coated with suitable materials that include by way of non-limiting examples: metals, such as vanadium, copper, cerium, and/or other materials. The coated materials effect chemical reactions to reduce, in the presence of ammonia, NOx molecules in the exhaust gas feedstream to form elemental nitrogen (N2) and other inert gases, under certain conditions of the exhaust gas feedstream related to temperature, flowrate, air/fuel ratio and others.

The first reductant delivery system <NUM> includes the single reductant injector <NUM> having an injection nozzle that is positioned to inject reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM>. The first reductant delivery system <NUM> is configured to controllably supply a metered flow of reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM> to facilitate NOx reduction therethrough.

The subsystem controller <NUM> is operatively connected to the first reductant delivery system <NUM> and in communication with the first exhaust gas sensor <NUM> and the first temperature sensor <NUM>. The subsystem controller <NUM> is also in communication, via the communication bus <NUM>, with the engine-out exhaust gas sensor <NUM>, the tailpipe exhaust gas sensor <NUM> and the second temperature sensor <NUM> that are arranged to monitor the base exhaust aftertreatment system <NUM>.

The subsystem controller <NUM> includes an instruction set that is executable to control the first reductant delivery system <NUM> to inject reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> based upon inputs from the engine-out exhaust gas sensor <NUM>, the first exhaust gas sensor <NUM>, the tailpipe exhaust gas sensor <NUM>, the first temperature sensor <NUM>, and the second temperature sensor <NUM>.

The modular exhaust subsystem <NUM> is a modular subsystem that may be employed to enable achievement of an ultra-low NOx emissions target, either in a production vehicle build, a retrofit, or an upfit to an existing vehicle or stationary system.

The modular exhaust subsystem <NUM> may be developed independently from the base exhaust aftertreatment system <NUM>, with the subsystem controller <NUM> being separate and independent from the second controller <NUM> that monitors and controls the base exhaust aftertreatment system <NUM>. As such the subsystem controller <NUM> is not integrated into the second controller <NUM> but is able to capture signal parameters from the second controller <NUM> to monitor and leverage the base exhaust aftertreatment system <NUM> to achieve a lower emissions target. The arrangement and configuration of the elements of the base exhaust aftertreatment system <NUM> do not require modifications to apply the modular exhaust subsystem <NUM>, and the base exhaust aftertreatment system <NUM> is not aware that the modular exhaust subsystem <NUM> has been added.

Several advantages exist with maintaining the base exhaust aftertreatment system <NUM> in an unaltered configuration, including enabling a modular hardware configuration wherein all vehicles in an assembly plant use the same base exhaust aftertreatment system <NUM> including hardware, controller, and software, with the modular exhaust subsystem <NUM> being a system add-on for specific vehicles, thus facilitating a flexible vehicle manufacturing environment. Furthermore, the second controller <NUM> can be maintained as an independent system for purposes of control and diagnostics. The second controller <NUM> retains controls for the second, underbody reductant delivery system <NUM> and maintenance/regeneration of the particulate filter <NUM>. The second controller <NUM> retains existing diagnostics for the base exhaust aftertreatment system <NUM>. Furthermore, the benefit of adding the modular exhaust subsystem <NUM> in the modular configuration is that the overall system efficiency is improved with a reduction in the tailpipe NOx emissions, thus allowing the engine to spend more time in more efficient modes, thereby improving fuel efficiency. In this manner, the incorporation of an embodiment of the modular exhaust subsystem <NUM> into a system that has been designed to have an embodiment of the base exhaust aftertreatment system <NUM> provides a mechanism to achieve reduced NOx emissions for an engine system in a manner that minimizes design, development, calibration, testing, and validation efforts, when compared to development of a complete emissions and engine control system to achieve reduced NOx emissions.

Referring again to <FIG>, the base exhaust aftertreatment system <NUM> is configured to purify the exhaust gas feedstream <NUM> to achieve a first tailpipe emissions target in-use. The base exhaust aftertreatment system <NUM> may be employed as a stand-alone system for use in systems to achieve the first tailpipe emissions target.

In one implementation, the base exhaust aftertreatment system <NUM> includes an exhaust aftertreatment device <NUM> that includes a second SCR catalyst <NUM>, a second reductant delivery system <NUM>, one or multiple temperature sensors, one or multiple exhaust gas sensors, and a second controller <NUM> that includes a second instruction set <NUM> for controlling the second reductant delivery system <NUM>. The second controller <NUM> communicates with other vehicle systems, e.g., an engine controller, via a communication bus <NUM>.

One non-limiting embodiment of the exhaust aftertreatment device <NUM> is illustrated. The exhaust aftertreatment device <NUM> includes a plurality of fluidly connected exhaust purifying devices for purifying engine exhaust gas prior to expulsion out the tailpipe to ambient air. An exhaust purifying device is a device that is configured to oxidize, reduce, filter and/or otherwise treat constituents of the exhaust gas feedstream <NUM>, including but not limited to hydrocarbons, carbon monoxide, nitrides of oxygen (NOx), particulate matter, and ammonia. In the non-limiting embodiment shown, first, second, third, and fourth exhaust purifying devices <NUM>, <NUM>, <NUM>, and <NUM>, respectively, are shown.

The first exhaust purifying device <NUM> may be an oxidation catalyst for oxidizing hydrocarbons and other constituents in the exhaust gas feedstream <NUM>, in certain embodiments, and is referred to hereafter as an oxidation catalyst <NUM>.

The second exhaust purifying device <NUM> is a particulate filter for filtering particulate matter from the exhaust gas feedstream.

The third exhaust purifying device <NUM> is also an SCR catalyst, i.e., the second SCR <NUM> in one embodiment.

In one embodiment, the second SCR catalyst <NUM> is a urea-based device that employs gaseous ammonia to react with and reduce NOx molecules to form elemental nitrogen (N2) and other inert gases. The injected reductant may be urea, which can be converted to ammonia (NH3), and stored on the substrate of the second SCR catalyst <NUM> to react with and reduce NOx molecules.

In one embodiment, a second heating device <NUM> may be interposed in the exhaust gas feedstream downstream of the second exhaust purifying device <NUM> and upstream of the third exhaust purifying device <NUM>, and may be, in one embodiment, an electrically-powered resistive heater or heating element, a burner, or another heater, to inject heat energy into the exhaust gas flow and the injected reductant.

The fourth exhaust purifying device <NUM> may be an oxidation catalyst that is arranged downstream of the second SCR catalyst <NUM> and operates to oxidize unused ammonia from the second SCR catalyst <NUM>.

The second reductant delivery system <NUM> includes a second reductant injector <NUM> having an injection nozzle that is positioned to inject reductant into the exhaust gas feedstream downstream of the second exhaust purifying device <NUM>, i.e., the particulate filter, and upstream of the second SCR catalyst <NUM>. The second reductant delivery system <NUM> is configured to controllably supply a metered flow of reductant into the exhaust gas feedstream upstream of the second SCR catalyst <NUM> to facilitate NOx reduction through the second SCR catalyst <NUM>.

Each of the first, second, third, and fourth exhaust purifying devices <NUM>, <NUM>, <NUM>, and <NUM>, respectively, includes a ceramic or metallic substrate having flow channels that have been coated with suitable materials that include by way of non-limiting examples: platinum-group metals such as platinum, palladium and/or rhodium; other metals, such as vanadium, copper, cerium, and/or other materials. The coated materials effect chemical reactions to oxidize, reduce, filter, or otherwise treat constituents of the exhaust gas feedstream under certain conditions related to temperature, flowrate, air/fuel ratio and others. The embodiment shown includes the elements of the base exhaust aftertreatment system <NUM> in one arrangement, which is illustrative.

Other arrangements of the elements of the base exhaust aftertreatment system <NUM> may be employed within the scope of this disclosure, with such arrangements including the addition of other exhaust purifying devices and/or omission of one or more of the exhaust purifying devices, depending upon requirements of the specific application.

The sensors for monitoring the various exhaust purifying devices of the base exhaust aftertreatment system <NUM> include the tailpipe exhaust gas sensor <NUM> and the second temperature sensor <NUM>. Other sensors (not shown) may include, for example, a particulate matter sensor, a delta pressure sensor for monitoring pressure drop across the SCR catalyst <NUM>, additional temperature sensors, and/or other sensing devices and models for monitoring the exhaust gas feedstream. The tailpipe exhaust gas sensor <NUM> may be a NOx sensor, and in one embodiment may have wide-range air/fuel ratio sensing capability. Such sensors and models may be arranged to monitor or otherwise determine parameters relegated to the exhaust gas feedstream at specific locations. As such, the aforementioned sensors and/or models may be advantageously employed to monitor performance of individual ones of the exhaust purifying devices, monitor parameters associated with performance of a subset of the exhaust purifying devices, or monitor parameters associated with performance of the base exhaust aftertreatment system <NUM>.

The second instruction set <NUM> is executed by the second controller <NUM> to control the second reductant delivery system <NUM> to achieve the first tailpipe emissions target in-use based upon signal inputs from the engine-out exhaust gas sensor <NUM>, the tailpipe exhaust gas sensor <NUM> and the second temperature sensor <NUM>.

The subsystem controller <NUM> includes the instruction set <NUM> that is executable by the subsystem controller <NUM> to control the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> based upon inputs from the first and second exhaust gas sensors and the first and second temperature sensors.

This includes the instruction set <NUM> being executed by the subsystem controller <NUM> to control the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM> to achieve a target reductant/NOx ratio that is provided as the exhaust gas feedstream that is input to the base exhaust aftertreatment system <NUM>.

Alternatively, or in addition, the subsystem controller <NUM> controls, via the instruction set <NUM>, the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> to achieve a target ammonia storage level on the first SCR catalyst <NUM> in anticipation of a projected need for NOx reduction, and as part of controlling the exhaust gas feedstream that is input to the base exhaust aftertreatment system <NUM>.

The subsystem controller <NUM> employs data inputs from the exhaust gas sensors and the temperature sensors that are monitoring the base exhaust aftertreatment system <NUM>, without affecting or changing control parameters associated with operation of the base exhaust aftertreatment system <NUM>.

The base exhaust aftertreatment system <NUM> is configured to purify the exhaust gas feedstream <NUM> to achieve a first tailpipe emissions target in-use. The base exhaust aftertreatment system <NUM> includes an exhaust aftertreatment device <NUM> that includes the SCR catalyst <NUM>, the second reductant delivery system <NUM>, one or multiple temperature sensors, one or multiple exhaust gas sensors, and the second controller <NUM> that includes the second instruction set <NUM> for controlling the second reductant delivery system <NUM>. The concepts described herein provide a modular subsystem that may be employed to enable achievement of an ultra-low NOx emissions target, either in a production vehicle build or a retrofit.

The term "controller" and related terms such as microcontroller, control, control unit, processor, etc. refer to one or various combinations of Application Specific Integrated Circuit(s) (ASIC), Field-Programmable Gate Array(s) (FPGA), electronic circuit(s), central processing unit(s), e.g., microprocessor(s) and associated non-transitory memory component(s) in the form of memory and storage devices (read only, programmable read only, random access, hard drive, etc.). The non-transitory memory component is capable of storing machine readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, signal conditioning, buffer circuitry and other components, which can be accessed by and executed by one or more processors to provide a described functionality. Input/output circuit(s) and devices include analog/digital converters and related devices that monitor inputs from sensors, with such inputs monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms mean controllerexecutable instruction sets including calibrations and look-up tables. Each controller executes control routine(s) to provide desired functions. Routines may be executed at regular intervals, for example every <NUM> microseconds during ongoing operation. Alternatively, routines may be executed in response to occurrence of a triggering event. Communication between controllers, actuators and/or sensors may be accomplished using a direct wired point-to-point link, a networked communication bus link, e.g., communication bus <NUM>, a wireless link, or another communication link. Communication includes exchanging data signals, including, for example, electrical signals via a conductive medium; electromagnetic signals via air; optical signals via optical waveguides; etc. The data signals may include discrete, analog and/or digitized analog signals representing inputs from sensors, actuator commands, and communication between controllers.

<FIG> each show composite emissions test results associated with operation of a vehicle system employing an embodiment of the engine <NUM>, including results associated with an embodiment employing only the base exhaust aftertreatment system <NUM> (Base EAS) that is described with reference to <FIG>, and results associated with an embodiment employing the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR). The first, second and third emissions targets may be defined by a regulatory agency associated with a political entity or defined by a private entity (such as a company that employs a fleet of vehicles) or defined by a specific manufacturer. It is appreciated that the emissions performance capabilities of the base exhaust aftertreatment system <NUM>, and of the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> are determined by factors associated with: engine control to achieve engine-out emissions targets; volumetric sizes and layouts of the exhaust aftertreatment devices; types and amounts of washcoats and catalytic materials; arrangement and operation of reductant injection system(s); and other factors. Thus, the emissions results described herein indicate relative improvements in emissions performance that can be obtained by the addition of an embodiment of the modular exhaust subsystem <NUM> upstream of an embodiment of the base exhaust aftertreatment system <NUM>, as compared to emissions performance that can be obtained by the embodiment of the base exhaust aftertreatment system <NUM> alone.

<FIG> graphically shows Composite FTP (Federal Test Procedure) emissions test results for tailpipe NOx emissions (in units of g/bHP-hr). On the system having only the base exhaust aftertreatment system <NUM> (Base EAS), a first emissions target (1st Target) is achieved, but neither a second emissions target (2nd Target) nor a third emissions target (3rd Target) are achieved. On the system having the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR), the first emissions target, the second emissions target, and the third emissions target are achieved.

<FIG> graphically shows composite RMC (Ramped Modal Cycle) emissions test results for tailpipe NOx emissions (in units of g/bHP-hr). On both the system having only the base exhaust aftertreatment system <NUM> (Base EAS), and the system having the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR), the first emissions target (1st Target), the second emissions target (2nd Target), and the third emissions target (3rd Target) are achieved.

<FIG> graphically shows composite LLC (Low Load Cycle) emissions test results for tailpipe NOx emissions (in units of g/bHP-hr). On the system having only the base exhaust aftertreatment system <NUM> (Base EAS), neither the second emissions target (2nd Target) nor the third emissions target (3rd Target) are achieved. On the system having the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR), the second emissions target (2nd Target) and the third emissions target (3rd Target) are achieved.

<FIG> graphically shows cumulative FTP emissions test results for tailpipe NOx emissions (in units of g/bHP-hr) in relation to time. On the system having only the base exhaust aftertreatment system <NUM> (Base EAS), the cumulative emissions increase throughout the test cycle. In contrast, on the system having the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR), the cumulative emissions increase only during the initial operation of a cold start, and then level off.

<FIG> graphically shows cumulative LLC emissions test results for tailpipe NOx emissions (in units of g/bHP-hr) in relation to time. On the system having only the base exhaust aftertreatment system <NUM> (Base EAS), the cumulative emissions increase throughout the test cycle. In contrast, on the system having the exhaust aftertreatment system <NUM> including the modular exhaust subsystem <NUM> arranged upstream of the base exhaust aftertreatment system <NUM> (Base EAS + Modular SCR), there may be no cumulative emissions.

Claim 1:
An exhaust aftertreatment system for a compression-ignition internal combustion engine (<NUM>), the exhaust aftertreatment system comprising a base exhaust aftertreatment system (<NUM>) and a modular exhaust subsystem (<NUM>) for purifying an exhaust gas feedstream (<NUM>) of the compression-ignition internal combustion engine (<NUM>) upstream of the base exhaust aftertreatment system (<NUM>), wherein the modular exhaust subsystem (<NUM>) is a stand-alone modular system configured for being inserted between the internal combustion engine (<NUM>) and the base exhaust aftertreatment system (<NUM>), the modular exhaust subsystem (<NUM>) comprising:
a selective catalytic reduction (SCR) catalyst (<NUM>),
a first exhaust gas sensor (<NUM>) and a first temperature sensor (<NUM>) arranged to monitor the SCR catalyst (<NUM>);
a reductant delivery system (<NUM>) arranged to inject a reductant into the exhaust gas feedstream (<NUM>) upstream of the SCR catalyst (<NUM>);
a controller (<NUM>), operatively connected to the reductant delivery system (<NUM>) and in communication with the first exhaust gas sensor (<NUM>) and the first temperature sensor (<NUM>),
the controller (<NUM>) being further in communication with a second exhaust gas sensor (<NUM>) and a second temperature sensor (<NUM>) that are arranged to monitor the base exhaust aftertreatment system (<NUM>); and
the controller (<NUM>) being further in communication with an engine-out exhaust gas sensor (<NUM>) arranged to monitor the exhaust gas feedstream (<NUM>) upstream of the SCR catalyst (<NUM>),
wherein the controller (<NUM>) includes an instruction set that is executable to control the reductant delivery system (<NUM>) to inject the reductant into the exhaust gas feedstream (<NUM>) upstream of the SCR catalyst (<NUM>) based upon inputs from the engine-out exhaust gas sensor (<NUM>), the first and second exhaust gas sensors (<NUM>, <NUM>) and the first and second temperature sensors (<NUM>, <NUM>),
wherein the instruction set is executable to control the reductant delivery system (<NUM>) to inject the reductant into the exhaust gas feedstream (<NUM>) upstream of the SCR catalyst (<NUM>) to achieve a target reductant/NOx ratio upstream of the base exhaust aftertreatment system (<NUM>).