Patent Description:
Although auto-ignited diesel engines are known to be more economical to run than spark-ignited engines, diesel engines inherently face challenges in the area of emissions. For example, diesel engine exhaust contains incompletely burned fuel known as particulate matter, or "soot". In addition to particulate matter, internal combustion engines including diesel engines produce a number of combustion products including hydrocarbons ("HC"), carbon monoxide ("CO"), nitrogen oxides ("NOx"), and sulfur oxides ("SOx"). Engine exhaust aftertreatment systems (EAS) can be utilized to reduce or eliminate emissions of these and other combustion products.

EAS include close coupled and downstream SCR units that include catalysts which, in combination with a diesel emission fluid (DEF) promote the conversion of NOx, in exhaust gas from an internal combustion engine, to water and nitrogen gas. A typical EAS also includes a diesel particulate filter (DPF) to remove diesel particulates or soot from the exhaust gas. Over time, soot collects in the DPF. A portion of the collected soot undergoes passive oxidation at temperatures of the exhaust gas flowing through the DPF; however, periodically the DPF must undergo an active regeneration in order to remove soot that is not removed by the passive oxidation. Active regeneration involves elevating the temperature of the exhaust gas within the DFP to about <NUM>° C. Such elevated temperatures can be achieved by oxidizing reductants, such as hydrocarbons, e.g., from the diesel fuel in the exhaust.

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

In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not necessarily intended to convey any information regarding the actual shape of the particular elements, and may have been solely selected for ease of recognition in the drawings.

The invention provides a method according to independent claim <NUM>.

<FIG> shows a block diagram providing a brief overview of a vehicle powertrain. The components include an internal combustion engine <NUM> in flow communication with one or more selected components of an emission aftertreatment system <NUM> (EAS). The illustrated emission aftertreatment system <NUM> includes an oxidation system <NUM> upstream of a particulate filter <NUM>. In the embodiment shown, the oxidation system <NUM> is a diesel oxidation catalyst (DOC) unit <NUM> coupled in flow communication to receive and treat exhaust from the engine <NUM>. The DOC <NUM> is preferably a flow-through device that includes either a honeycomb-like or plate-like substrate. The DOC substrate has a surface area that includes (e.g., is coated with) a catalyst. The catalyst can be an oxidation catalyst, which can include a precious metal catalyst, such as platinum or palladium, for rapid exothermic conversion of hydrocarbons, carbon monoxide, and nitric oxides in the engine exhaust gas into carbon dioxide, nitrogen, water, or NO<NUM>.

Once the exhaust flows through DOC <NUM> it flows into the particulate filter <NUM>, which in the illustrated embodiment is a diesel particulate filter (DPF) <NUM>. The DPF <NUM> is utilized to capture unwanted diesel particulate matter (e.g., soot) from the flow of exhaust gas exiting engine <NUM>, by flowing exhaust across the walls of channels within DFP <NUM>. The diesel particulate matter includes sub-micron sized solid and liquid particles found in exhaust of a diesel fueled internal combustion engine. The DPF <NUM> can be manufactured from a variety of materials including but not limited to cordierite, silicon carbide, and/or other high temperature oxide ceramics. In order to elevate the temperature of the exhaust gas to a level that will promote oxidation of soot built up in DPF <NUM> (e.g., an active regeneration of the DPF), a reductant, such as a hydrocarbon, e.g., from the diesel fuel is introduced into the exhaust gas upstream of the DOC. Such reductant will be oxidized in the DOC. Oxidation of the reductant will have the effect of increasing the temperature of the exhaust gas within the DOC. The exhaust gas which has been heated in the DOC flows to the DPF. During an active regeneration of the DPF, the temperature of the exhaust gas entering the DPF is greater than about <NUM>° C, which is sufficient to oxidize soot within DPF that is not removed by passive regeneration.

From DPF <NUM>, exhaust gases proceed through a compartment in fluid communication with a diesel exhaust fluid (DEF) doser <NUM>. Operation of DEF doser introduces a reductant, such as ammonia or a urea solution, into the exhaust gases. The exhaust gases and reductant then flow to a selective catalytic reduction (SCR) system or unit <NUM> which includes a catalytic core having a selective catalytic reduction catalyst (SCR catalyst) loaded thereon. System <NUM> can include one or more sensors (not illustrated in <FIG> associated with components of the system <NUM>, such as one or more temperature sensors, NOx sensors, NH<NUM> sensors, oxygen sensors, mass flow sensors, volumetric flow sensors, particulate sensors, and a pressure sensors.

As discussed above, the emission aftertreatment system <NUM> includes a Selective Catalytic Reduction (SCR) system <NUM>. The SCR system <NUM> includes a selective catalytic reduction catalyst which interacts with NOx gases to convert the NOx gases into N<NUM> and water, in the presence of an ammonia reductant. The overall reactions of NOx reductions in SCR are shown below.

4NO + 4NH<NUM> + O<NUM> → 4N<NUM> + <NUM><NUM>O     (<NUM>).

6NO<NUM> + 8NH<NUM> → 7N<NUM> + <NUM><NUM>O     (<NUM>).

2NH<NUM> + NO + NO<NUM> → 2N<NUM> + <NUM><NUM>O     (<NUM>).

Where Equation (<NUM>) represents a standard SCR reaction and Equation (<NUM>) represents a fast SCR reaction.

As a consequence of the typical configuration of an EAS with a primary SCR unit <NUM> downstream of the DOC <NUM> and DPF <NUM>, the SCR unit <NUM> downstream of the DOC <NUM> and DPF <NUM> cannot avoid exposure to the high temperature exhaust gas which passes through the DPF <NUM> during an active regeneration of DPF <NUM>. Referring to <FIG>, when the temperature of exhaust gas entering SCR unit <NUM> is above about <NUM>° C, e.g., such as experienced during active regeneration of DPF <NUM>, the NOx conversion efficiency of SCR unit <NUM> downstream of the DPF <NUM> declines. When the SCR unit <NUM> is exposed to exhaust gases that have been heated to about <NUM>° C in DOC <NUM>, <FIG> shows that the NOx conversion efficiency of SCR unit <NUM> is well below the NOx conversion efficiency of the SCR unit when the temperature of the exhaust gas entering SCR unit <NUM> is between about <NUM>° and <NUM>° C. , e.g., less than <NUM>%. Such reduced NOx conversion efficiency in SCR unit <NUM> can result in NOx emissions from the EAS that are outside prescribed limits or cause the EAS system to fall out of compliance with prescribed regulations.

Referring to <FIG>, an EAS according to the present invention includes a "close-coupled SCR" or "upstream SCR" <NUM> associated with a DEF doser <NUM> that is located upstream of the close-coupled SCR <NUM>. The close-coupled SCR <NUM> is located closer to the engine <NUM> than the downstream SCR <NUM> (sometimes referred to as an under-body SCR or downstream SCR unit) and in some embodiments as close to the engine as possible. An example of a close-coupled SCR configuration is illustrated in <FIG>. Such close-coupled SCR configuration employs DEF doser <NUM> and DEF doser <NUM> (one upstream of the close-coupled SCR <NUM> and one upstream of the downstream SCR <NUM> and downstream of the close-coupled SCR <NUM>.

<FIG> illustrates an example of the EAS described above with reference to <FIG> with the addition of additional features. In <FIG>, features that are identical to features illustrated in <FIG> are identified by the same reference numbers as used in <FIG>. For example, EAS illustrated in <FIG> includes first DEF doser <NUM>, upstream SCR unit <NUM>, a reductant source <NUM> downstream of the upstream SCR unit <NUM>, diesel oxidation catalyst unit <NUM>, diesel particulate filter <NUM>, second DEF doser <NUM> and downstream SCR unit <NUM>. In the embodiment illustrated in <FIG>, downstream SCR <NUM> is illustrated as included two bricks of substrates supporting SCR catalyst(s). Reductant source <NUM> introduces a reductant, such as a hydrocarbon, into the exhaust gas between the close coupled SCR unit <NUM> and the DOC <NUM>. Such reductant is available to be oxidized by the catalyst in the DOC <NUM>. Oxidation of the reductant will have the effect of increasing the temperature of the exhaust gas within the DOC <NUM>. The exhaust gas which has had its temperature elevated in the DOC <NUM> flows to the DPF <NUM>. When the temperature of the exhaust gas entering the DPF <NUM> is greater than about <NUM>° C, soot within DPF <NUM> is oxidized and active regeneration of the DPF is accomplished.

EAS illustrated in <FIG> further includes a plurality of NOx sensors <NUM>. A NOx sensor 116a is located upstream of DEF doser <NUM>. NOx sensor 116b is located downstream of upstream SCR <NUM> and upstream of DOC <NUM>. NOx sensor 116c is positioned downstream of downstream SCR <NUM>. Such NOx sensors are designed to detect concentrations of NOx in the exhaust gas; however, such NOx sensors used in EAS are often unable to differentiate between NOx in the exhaust gas and ammonia in the exhaust gas. Accordingly, signals generated by the NOx sensors are an indication of the concentration or amount of the combination of NOx and ammonia in the exhaust gas the sensor is interrogating. In the embodiment illustrated in <FIG>, the EAS includes a thermal input device <NUM>, e.g., an electric heater downstream of DEF doser <NUM> and upstream of SCR unit <NUM>. This thermal input device <NUM> is used to introduce thermal energy into the exhaust gas, thereby increasing the temperature of the exhaust gas flowing into the close coupled SCR unit <NUM>. The temperature of the exhaust gas flowing into the close coupled SCR unit <NUM> can also be adjusted through the implementation of an exhaust gas recirculation system which recirculates a portion of the exhaust gas to the internal combustion engine. Adjusting the temperature of the exhaust gas flow into the close coupled SCR unit <NUM> is one way to adjust the temperature of the catalyst in the SCR unit <NUM>. While the embodiment of an EAS illustrated in <FIG> includes two SCR units <NUM> and <NUM>, embodiments of the present invention include an EAS that includes more than two SCR units and methods in accordance with embodiments of the present invention can be practiced in an EAS that includes two or more SCR units.

In accordance to the present invention a DPF of an EAS, including a close coupled SCR unit and a downstream SCR unit, is actively regenerated while maintaining the NOx emissions from the EAS within prescribed limits. In accordance with some embodiments described herein, reductant, which will be oxidized in the DOC, is introduced into the exhaust gas downstream of the close coupled SCR unit as part of an active regeneration of the DPF. This reductant is oxidized in the DOC thereby raising the temperature of the exhaust gas to levels that promote oxidation of soot in the DPF, but also to levels where the NOx conversion efficiency of the downstream SCR unit decreases significantly. According to the invention during the active regeneration of the DPF, DEF is dosed to the exhaust gas upstream of the close coupled SCR unit and the close coupled SCR unit operates as a primary device to reduce the NOx content of the exhaust gas. During the active regeneration of the DPF <NUM>% or more, <NUM>% or more, or <NUM>% or more of the overall NOx reduction provided by the EAS is provided by the close coupled SCR unit. Overall NOx reduction by the EAS refers to the difference between NOx content of the exhaust gas entering the close coupled SCR unit and the NOx content of the exhaust gas exiting the downstream SCR unit.

Referring to <FIG>, in accordance with an embodiment of the present invention a method <NUM> of operating in EAS to regenerate a DPF starts at step <NUM>. In accordance with method <NUM>, at step <NUM> a reductant is introduced by reductant doser <NUM> into the exhaust gas downstream of close coupled SCR unit <NUM>. The mixture of reductant and exhaust gas flows to DOC <NUM> at step <NUM>. At step <NUM>, within DOC <NUM>, the reductant is oxidized which results in the temperature of the exhaust gas increasing at step <NUM>. The exhaust gas at the elevated temperature within DOC <NUM> flows to DPF <NUM> at step <NUM>. Due to the elevated temperature of the exhaust gas, soot within DPF <NUM> is oxidized and DPF <NUM> is actively regenerated in step <NUM>. In accordance with embodiments of the present invention, at step <NUM>, while such active regeneration and oxidation of soot within DPF <NUM> is occurring, DEF is dosed from DEF doser <NUM> into the exhaust gas and the NOx content of the exhaust gas entering close coupled SCR unit <NUM> is reduced.

In accordance with an embodiment of the present invention, an amount of reductant introduced by reductant doser <NUM>, at step <NUM>, is sufficient to elevate the temperature of the exhaust gas to <NUM>° C via an exothermic oxidation of the reductant in the DOC <NUM>. In other embodiments, an amount of reductant introduced by reductant doser <NUM>, at step <NUM>, is sufficient to elevate the temperature of the exhaust gas to <NUM>° C or more via an exothermic oxidation of the reductant in DOC <NUM>.

In accordance with an embodiment of the present invention, during the active regeneration of DPF <NUM>, close coupled SCR unit <NUM> reduces the NOx content of the exhaust gas by an amount that is <NUM>% or more, <NUM>% or more, or <NUM>% or more of the overall NOx reduction provided by the EAS. As discussed above, overall NOx reduction by the EAS refers to the difference between NOx content of the exhaust gas entering the close coupled SCR unit and the NOx content of the exhaust gas exiting the downstream SCR unit.

<FIG> illustrates a schematic diagram of a vehicle <NUM>, which may be a heavy-duty vehicle, with an internal combustion engine <NUM>, which may be a diesel engine, an exhaust after-treatment system <NUM>, a set of at least four wheels <NUM> configured to be powered and driven by the engine <NUM>, and a control system <NUM>, which can perform the methods described herein. When the vehicle <NUM> is in operation, the control system <NUM> can be used to control operation of portions of the vehicle <NUM>, including its internal combustion engine <NUM> and its emission after-treatment system <NUM>. For example, the control system <NUM> may be configured to control the engine <NUM> to idle with any number of its cylinders firing and any number of its cylinders deactivated, to control the engine <NUM> to increase the load on the engine <NUM>, for example by driving an electric generator (not shown), to direct electrical energy generated by the electrical generator into an exhaust gas stream at a location between the engine <NUM> and the emission after-treatment system <NUM>, to increase or decrease the temperature of the gases exhausted from the engine and/or to increase or decrease the volumetric flow of air through the engine. These examples of functions the control system <NUM> is able to control or initiate are not exhaustive. The control system <NUM> in accordance with embodiments of the present invention may be able to control or initiate other functions of the engine or vehicle. As another example, the control system <NUM> may be configured to control the exhaust after-treatment system <NUM> and components thereof, including a diesel oxidation catalyst (DOC) unit to oxidize unburned fuel and carbon monoxide, a diesel particulate filter (DPF) to control particulate matter (PM), a selective catalytic reduction (SCR) system or unit to reduce oxides of nitrogen (NOX), and an ammonia oxidation catalyst (AMOX) system. For example, in some embodiments, the control system <NUM> is configured to control an amount of reductant to be oxidized in the DOC during an active regeneration of a DPF and to dose DEF into exhaust gas upstream of a close coupled SCR unit during the active regeneration of the DPF.

In some embodiments, the vehicle <NUM> includes a plurality of sensors that collect and transmit data regarding operating parameters of the vehicle <NUM> and/or operating parameters of the EAS to the control system <NUM>, such as continuously. For example, such sensors may collect and transmit data regarding an exhaust gas temperature, volumetric flow rate of exhaust gases, volumetric air flow rate to engine, fuel/air ratio to engine, temperature of air flow to engine, NOx content of the exhaust gas, NOx content of exhaust gas exiting the SCR units, volumetric flow of DEF dosing, temperature of the engine, an operating speed of the internal combustion engine <NUM> (e.g., in RPM) to the control system <NUM>, load on the engine, temperature of SCR unit and level of exhaust gas recirculation (EGR). Other sensors may collect and transmit data regarding the EAS. For example, such sensors can collect and transmit data regarding an amount of NOx entering an upstream SCR or entering a downstream SCR, amount of NOx out of an upstream SCR or out of a downstream SCR, quantity of DEF dosing and temperature of upstream and/or downstream SCR units.

<FIG> shows one non-limiting example of an emissions aftertreatment system controller <NUM> formed in accordance with aspects of the present invention and can be part of the control system <NUM>. The control system may be an emissions management system associated with an EAS system of a vehicle powered by an internal combustion engine or an EAS of an internal combustion engine implemented in a stationary application. The controller <NUM> is connected in electrical communication with a plurality of data sources 200a-200n (generally, data sources <NUM>). As will be described in more detail below, the data sources <NUM> may include but are not limited to on-board sensors, e.g., engine sensors and EAS sensors, on-board state estimators, etc. It will be appreciated that the controller <NUM> can be connected directly (wired or wirelessly) to the plurality of data sources <NUM> or indirectly via any suitable interface, such as a CAN interface <NUM>. Those skilled in the art and others will recognize that the CAN <NUM> may be implemented using any number of different communication protocols such as, but not limited to, Society of Automotive Engineers ("SAE") J1587, SAE J1922, SAE J1939, SAE J1708, and combinations thereof. The controller <NUM> may also communicate with other electronic components of the vehicle <NUM> via the CAN <NUM> for collecting data from other electronic components to be utilized by the controller <NUM>, and as such, can also be considered in at least some embodiments as data sources <NUM>. For example, the controller <NUM> may receive data from one or more other controllers <NUM>, such as an engine controller, a transmission controller, a brake system controller, etc. In operation, as will be described in more detail below, the controller <NUM> receives signals from the data sources <NUM>, processes such signals and others, and depending on the processed signals, transmits suitable control signals for operating the EAS <NUM>, the engine <NUM> or other systems or components of the vehicle <NUM>. The controller <NUM> initiates operation by means of a hard wired input (e.g. ignition key <NUM>) or by receiving a signal from a communication network (e.g. wake-up on CAN). This wake-up message allows to bring the controller <NUM> in operation, whereas the operator does not need to use the ignition keys or be physically in or near the vehicle <NUM>. The controller <NUM> may be a standalone controller or may be part of one or more other controllers (e.g., vehicle electronic control unit (VECU)) of the vehicle <NUM>. Generally, the emission aftertreatment system may be implemented in any local or remote controller(s) operative to provide the functionality described herein.

In at least some embodiments, the controller <NUM> may contain logic rules implemented in a variety of combinations of hardware circuitry components and programmed processors to effect control of the EAS <NUM> and other systems of the vehicle <NUM>. To that end, as further illustrated in <FIG>, one suitable embodiment of the controller <NUM> includes a nontransitory memory <NUM>, a processor <NUM>, and emissions management control module <NUM> for providing functionality of the controller <NUM>. The memory <NUM> may include computer readable storage media in read-only memory (ROM) <NUM> and random-access memory (RAM) <NUM>, for example. The computer-readable storage media may be implemented using any of a number of memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory devices capable of storing data, including data <NUM> (e.g., programmable parameters). The controller <NUM> also includes one or more input/output devices or components <NUM> that enable the controller to communicate with one or more local or remote devices via wired or wireless communication. In at least some embodiments, the controller <NUM> may include additional components including but not limited to a high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, other input/output circuitry and devices (I/O), and appropriate signal conditioning and buffer circuitry.

As used herein, the term processor is not limited to integrated circuits referred to in the art as a computer, but broadly refers to one or more of a microcontroller, a microcomputer, a microprocessor, a central processing unit (CPU), a graphics processing unit (GPU), a programmable logic controller, an application specific integrated circuit, other programmable circuits, combinations of the above, among others. In at least one embodiment, the processor <NUM> executes instructions stored in memory <NUM>, such as engine restart control module <NUM>, to implement the functionality described in the present invention.

The emissions management control module <NUM> may include a set of control algorithms, including program instructions, selectable parameters, and calibrations stored in one of the storage media and executed to provide functions described herein. Information transfer to and from the module <NUM> may be accomplished by way of a direct connection, a local area network bus, a serial peripheral interface bus, wired or wireless interfaces, etc. The algorithms may be executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices may be executed by the processor <NUM> to monitor inputs from the sensing devices and other data transmitting devices or polls such devices for data to be used therein. Loop cycles may be executed at regular intervals during ongoing operation of the vehicle <NUM>. Alternatively or additionally, algorithms may be executed in response to the occurrence of one or more events.

The processor <NUM> communicates with various data sources <NUM> directly or indirectly via the input/output (I/O) interface <NUM> and suitable communication links. The interface <NUM> may be implemented as a one or more integrated interfaces that provide various raw data or signal conditioning, processing, and/or conversion, short-circuit protection, and/or the like. Additionally or alternatively, one or more dedicated hardware or firmware chips may be used to condition and process particular signals before being supplied to the processor <NUM>. In at least some embodiments, the signals transmitted from the interface <NUM> may be suitable digital or analog signals.

The controller <NUM> may be a separate controller that implements the EAS management functionality described herein. However, it should be appreciated that the controller <NUM> may be a controller module, which could be software embedded within an existing on-board controller, such as the engine controller, a general purpose controller, other vehicle system controllers, etc..

As briefly described above, the data sources <NUM> can include but are not limited to on-board sensors for detecting operation parameters of an EAS, navigation/GPS devices, communications devices, data stores, remote servers, etc. These data sources and others in at least some embodiments may be part of the electrical systems <NUM>, control console <NUM>, etc., described above. The data supplied from these data sources <NUM> and others may generally or specifically relate to vehicle operating parameters, e.g., engine or EAS operating parameters, operator driving trends and accessories (e.g., loads <NUM>) usage patterns and characteristics, and external parameters, including present vehicle navigation, traffic patterns, weather data, sunrise and sunset data, temperature data, among others.

Claim 1:
A method (<NUM>) of operating an emissions aftertreatment system, EAS, including a close coupled SCR unit (<NUM>) and a downstream SCR unit (<NUM>), the method comprising:
introducing a diesel exhaust fluid (<NUM>) into an exhaust gas from an internal combustion engine (<NUM>) upstream of the close coupled SCR unit;
introducing (<NUM>) a reductant (<NUM>) into the exhaust gas downstream of the close-coupled SCR unit and upstream of the downstream SCR unit;
flowing (<NUM>) the reductant and the exhaust gas into a diesel oxidation catalyst, DOC, unit (<NUM>);
oxidizing (<NUM>) the reductant in the DOC unit;
increasing (<NUM>) the temperature of the exhaust gas in the DOC unit;
flowing (<NUM>) the exhaust gas from the DOC unit to a diesel particulate filter, DPF, unit;
oxidizing (<NUM>) soot in the DPF unit; and
during the oxidizing soot, reducing (<NUM>) the NOx content of the exhaust gas in the close coupled SCR unit, CHARACTERIZED IN THAT during the oxidizing soot in the DPF unit further comprises:
- introducing thermal energy to the exhaust gas downstream of where the diesel exhaust fluid flows into the exhaust gas stream and upstream of the close coupled SCR unit,
- adjusting the temperature of the exhaust gas flowing into the close coupled SCR unit, and
- reducing an overall NOx content of the exhaust gas in the close coupled SCR unit, over <NUM> percent of the reduction in the overall NOx content of the exhaust gas provided by the close coupled SCR unit,
wherein the introducing thermal energy to the exhaust gas downstream of where the diesel exhaust fluid flows into the exhaust gas stream and upstream of the close coupled SCR unit includes introducing thermal energy to the exhaust stream utilizing an electric heater.