Patent Grant
10145284
The subject disclosure relates to automotive vehicle exhaust systems, and more particularly, to automotive vehicle exhaust treatment systems.
Automotive internal combustion engines emit exhaust gas that includes carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOx). Therefore, automotive vehicles typically include exhaust treatment systems for removing particulate matter and reducing regulated constituents from exhaust gas produced by the engine before expelling the exhaust gas from the vehicle. Exhaust treatment systems typically include a selective catalytic reduction (SCR) device that converts NOx into diatomic nitrogen (N2) and water (H2O) in the presence of a reductant catalyst such as ammonia (NH3), for example, thereby reducing the level of NOx emissions expelled from the vehicle.
In a non-limiting embodiment, an automotive vehicle includes an internal combustion engine and a dosing system. The internal combustion engine is configured to combust an air/fuel mixture to generate an exhaust gas stream containing oxides of nitrogen (NOx). The dosing system injects NH3 into the exhaust gas stream to generate a mixture of NH3 and exhaust gas. A selective catalyst reduction (SCR) device is configured to store an amount of the NH3, and to convert the NOx into diatomic nitrogen (N2) and water (H2O) based on the stored amount of the NH3. The vehicle further includes an SCR status estimator device in signal communication with an electronic hardware controller. The SCR status estimator device is configured to determine an NH3 coverage ratio (R), which is indicative of a stored amount of NH3 with respect to a maximum NH3 storage capacity of the SCR device. The controller is configured to determine a target NOx reduction efficiency (ηNOx) of the SCR device, and to determine an NH3 coverage ratio set point (Rsp) based on the ηNOx. The controller also generates an NH3 control signal (u) that controls the dosing system based on a comparison between the R and the Rsp. The dosing system injects an amount of the NH3 in response to the NH3 control signal (u).
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the controller is configured to determine a deviation between the R and the Rsp, and to adjust the amount of NH3 injected into the exhaust gas stream in response to the deviation.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a NOx sensor configured to output a NOx signal indicating a mass concentration of the NOx.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the SCR status estimator device is an Extended Kalman Filter (EKF) including an input that receives the SCR outlet NOx sensor signal and an output in signal communication with the controller. The EKF estimates a concentration of slipped NH3 (ĈNH3) released by the SCR device, and a concentration of NOx exiting the SCR device.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the EKF is configured to estimate the R and the ĈNH3 based on a physical linear dynamical model of the SCR device.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the controller wherein the controller determines a temperature of the SCR device, updates ηNOx_sp in response to the temperature exceeding a temperature threshold, and computes an updated Rsp based on the updated ηNOx_sp.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the controller determines the amount of NH3 to be injected into the exhaust gas stream based further on the ĈNH3.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the controller adjusts the amount of NH3 injected into the exhaust gas stream to reduce the ĈNH3.
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the controller adjusts the amount of NH3 injected into the exhaust gas stream in response to the deviation such that the ηNOx is maintained within a ηNOx threshold range.
In another non-limiting embodiment, a sliding mode selective catalyst reduction (SCR) control system included with an exhaust treatment system of an automotive vehicle comprises an NH3 coverage ratio controller configured to determine an NH3 coverage ratio set point (Rsp) that operates an SCR device at a selected NOx reduction efficiency set point (ηNOx_SP). The sliding mode SCR control system further includes an SCR status estimator device and a NH3 sliding-mode-control (SMC) module. The SCR status estimator device is configured to estimate an NH3 coverage ratio (R) of the SCR device, a concentration of slipped NH3 (ĈNH3) released by the SCR device, and a concentration of NOx exiting the SCR device. The R is indicative of an amount of NH3 stored by the SCR device with respect to a maximum NH3 storage capacity of the SCR device. The NH3 SMC module is configured to monitor the R and to determine a deviation between R with respect to the Rsp. The sliding mode SCR control system further includes a NH3 calculator module configured to generate an NH3 control signal (u) indicating the amount of NH3 to be injected based on the deviation. A dosing system is configured to inject the corrected amount of NH3 based on the NH3 control signal (u).
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the amount of NH3 injected according to the u reduces the deviation between R and Rsp such that the ηNOx_SP is maintained.
In addition to one or more of the features described herein, or as an alternative, further embodiments include an NH3 slip detection controller in signal communication with the SCR status estimator device. The NH3 slip detection controller is configured to determine an NH3 slip event in response to the ĈNH3 exceeding an NH3 slip threshold value (CNH3_TH).
In addition to one or more of the features described herein, or as an alternative, further embodiments include a feature, wherein the NH3 slip detection controller generates a NH3 slip correction value (uNH3SLIP) that modifies the u in response to determining the NH3 slip event.
In yet another non-limiting embodiment, a method controls a NOx reduction efficiency of a vehicle exhaust treatment system. The method comprises combusting an air/fuel mixture to generate exhaust gas stream containing oxides of nitrogen (NOx), and injecting NH3 into the exhaust gas stream, via a dosing system, to generate a mixture of NH3 and exhaust gas. The method further comprises storing the injected NH3, via a selective catalyst reduction (SCR) device included in the exhaust treatment system, and converting the NOx into diatomic nitrogen (N2) and water (H2O) based on the stored amount of the NH3. The method further includes determining a NOx reduction efficiency set point (ηNOx_SP) indicative of a selected NOx reduction efficiency of the SCR device, and determining an NH3 coverage ratio set point (Rsp) indicative of a stored amount of NH3 with respect to a maximum NH3 storage capacity of the SCR device for reaching the ηNOx_SP. The method further includes estimating an NH3 coverage ratio (R) indicative of an actual amount of the stored NH3 with respect to the maximum NH3 storage capacity of the SCR device, and generating an NH3 control signal (u) based on a comparison between the R and the Rsp, the u controlling the amount of NH3 injected by the dosing system.
In addition to one or more of the features described herein, or as an alternative, further embodiments include determining a deviation between the R and the Rsp, and adjusting the amount of NH3 injected into the exhaust gas stream in response to the deviation.
In addition to one or more of the features described herein, or as an alternative, further embodiments include estimating R based on each of a mass concentration of the NOx exiting the SCR device, and an estimated concentration of slipped NH3 (ĈNH3) released by the SCR device.
In addition to one or more of the features described herein, or as an alternative, further embodiments include estimating the R and the ĈNH3, via an Extended Kalman Filter (EKF), based on a physical linear dynamical model of the SCR device.
In addition to one or more of the features described herein, or as an alternative, further embodiments include monitoring a temperature of the SCR device, updating ηNOx_sp in response to the temperature exceeding a temperature threshold, and computing an updated Rsp based on the updated ηNOx_sp.
In addition to one or more of the features described herein, or as an alternative, further embodiments include determining the amount of NH3 to be injected into the exhaust gas stream based further on the ĈNH3.
In addition to one or more of the features described herein, or as an alternative, further embodiments include adjusting the amount of NH3 injected into the exhaust gas stream to reduce the ĈNH3.
In addition to one or more of the features described herein, or as an alternative, further embodiments include adjusting the amount of NH3 injected into the exhaust gas stream in response to the deviation such that the ηNOx is maintained within a ηNOx threshold range.
The above features and advantages, and other features and advantages of the disclosure are readily apparent from the following detailed description when taken in connection with the accompanying drawings.
Other features, advantages and details appear, by way of example only, in the following detailed description, the detailed description referring to the drawings in which:
The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
SCR devices store a limited amount of NH3 due to the limited volume of the SCR catalyst. The ratio of stored NH3 with respect to the maximum storage capacity of the SCR catalyst is referred to herein as the actual NH3 coverage ratio (i.e., “R”). The value of R has a mutual correlation with respect to the efficiency of the SCR device to reduce the amount of NOx from the exhaust gas stream.
The efficiency of the SCR device is referred to herein as NOx reduction efficiency (ηNOx). For instance, ηNOx is improved as the calculated value representing R is brought closer to “1”. The ηNOx value can be computed as a percentage defined in the range [0%-100%]. As the SCR device operates at a higher efficiency, i.e. ηNOx brought closer to 100%, the amount of NOx removed from the exhaust gas stream is increased. Based on the correlation between R and ηNOx, the ηNOx of the SCR device can be increased as R is brought closer to “1”.
Variations in NOx levels generated by the engine due to vehicle speed transient conditions, altitude variations, and/or combustion modes, for example, can create NH3 slip conditions which impact the ability of the SCR catalyst to store NH3. In addition, temperature increases of the SCR catalyst can lower its capability to store NH3. Therefore, as the SCR catalyst temperature increases, NH3 delivery into the exhaust gas stream is typically adjusted to ensure acceptable SCR performance is maintained while also aiming to prevent NH3 slip.
Exhaust treatment systems utilize NH3 injection set points to control the delivery of NH3 into the exhaust gas stream. The NH3 injection set points are stored in the memory of a hardware controller installed on the vehicle, and adjusted according to a temperature of the SCR catalyst to determine the amount of NH3 to inject at a given vehicle operating condition. However, non-linear engine operating conditions such as high-speed transient conditions (e.g., vehicle accelerations), for example, can cause sudden increments in both the SCR catalyst temperature and NOx concentration, which in turn can increase the NOx emissions and NH3 slip if the amount of NH3 injected into the exhaust gas stream is not adjusted properly. Consequently, determining the NH3 injection set points based solely on SCR catalyst temperatures can cause an imprecise amount of NH3 to be injected into the exhaust gas stream, resulting in an inefficient NH3 consumption and poor NOx reduction efficiency.
In one or more embodiments described herein, the controller computes a novel set point referred to as an NH3 coverage ratio set point (Rsp). The Rsp value is computed as a function of ηNOx. For example, Rsp can be calculated as a selected R for achieving a target ηNOx, or maintaining ηNOx within a target ηNOx threshold range. Thus, a target ηNOx at a given vehicle operating condition can be selected using a ηNOx set point (ηNOx_sp), and the controller can compute the Rsp necessary to achieve the ηNOx_sp. A dosing system is then controlled to inject the correct amount of NH3 into the exhaust gas stream to maintain R at Rsp, or near, Rsp, thereby improving the overall operating efficiency of the SCR device. In another embodiment, the controller can actively compute Rsp as vehicle operating conditions change. Therefore, the SCR device can be operated at a selected ηNOx while taking into account the changing vehicle conditions.
Referring now to
The engine 12 includes one or more cylinders 18, an intake manifold 21, a mass air flow (MAF) sensor 22, and an engine speed sensor 24. Air 20 flows into the engine 12 via the intake manifold 21 and is monitored by the MAF sensor 22. The air 20 is directed into the cylinder 18 and is combusted with fuel to drive pistons (not shown). Although a single cylinder 18 is illustrated, it can be appreciated that the engine 12 may include additional cylinders 18. For example, the engine system 10 can implement an engine 12 having 2, 3, 4, 5, 6, 8, 10, 12 and 16 cylinders. Exhaust gas is produced inside the cylinder 18 resulting from a combustion of air and fuel.
The exhaust system 13 further includes an exhaust treatment system 14 and a dosing system 16. The exhaust treatment system 14 treats an exhaust gas stream 11 delivered, via an exhaust manifold 26, before it is released to the atmosphere. The exhaust treatment system 14 may include an oxidation catalyst (OC) device 28, a selective catalyst reduction (SCR) device 30, and a particulate filter (PF) device 36 such as, for example, a diesel PF (DPF). As can be appreciated, the exhaust treatment system 14 of the present disclosure may include other combinations of exhaust treatment devices (not shown).
The OC device 28 can be one of various flow-through, oxidation catalyst devices known in the art. The OC device 28 may include an OC substrate having an oxidation catalyst compound disposed thereon. The oxidation catalyst compound may be applied as a washcoat and may contain platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh) or other suitable oxidizing catalysts, or combination thereof. The OC device 28 is useful in treating unburned gaseous and non-volatile HC and CO, which are oxidized to form carbon dioxide (Co2) and water (H2O).
The SCR device 30 may be disposed downstream of the OC device 28, and is configured to reduce NOx constituents that are present in the exhaust gas stream 11. In various embodiments, the SCR device 30 can be constructed using a flow-through monolith SCR substrate (not shown), including an SCR catalyst composition (e.g., an SCR washcoat) applied thereon. The SCR device 30 utilizes a reductant such as NH3, for example, to assist in reducing a level of NOx from the exhaust gas stream 11. More specifically, the SCR catalyst composition can contain a zeolite and one or more base metal components such as iron (Fe), cobalt (Co), copper (Cu) or vanadium (V) which operates to decompose NOx constituents in the presence of NH3. The NH3 utilized by the SCR device 30 may be in the form of a gas, a liquid, or an aqueous solution and can be delivered into the exhaust gas stream 11 by the dosing system 16, as discussed herein.
The PF device 36 is disposed downstream from the SCR device 30, and filters the exhaust gas stream 11 of carbon and other particulate matter (e.g. soot). According to at least one exemplary embodiment, the PF device 36 may be constructed using a ceramic wall flow monolith substrate (not shown) that traps particulate matter as the exhaust gas stream 11 travels therethrough. It is appreciated that the ceramic wall flow monolith substrate is merely exemplary in nature and that the PF device 36 may include other filter devices such as wound or packed fiber filters, open cell foams, sintered metal fibers, etc. To enhance the performance of the PF device 36, a catalytic material can be applied to the PF substrate. The PF catalyst promotes oxidation of hydrocarbons, carbon monoxide (CO), soot, and particulate matter trapped in the PF substrate under conditions that cause exothermic reactions in the PF substrate.
The exhaust treatment system 13 can also include a PF regeneration system 15. The PF regeneration system 15 performs a regeneration process that cleans the PF device 36 by burning off the particulate matter trapped in the PF substrate. Such a system is known and, therefore, will not be discussed further.
Additional sensors may also be employed to monitor various operating conditions. For example, a pressure sensor 27 determines an exhaust pressure at a given vehicle operating condition. An exhaust gas flow rate sensor 29 can be positioned between the engine 12 and the OC device 28, and measures the flow rate of the exhaust gas stream 11. An exhaust temperature sensor 31 can be positioned between the engine 12 and the OC device 28 to measure the temperature of the exhaust gas stream 11. An inlet temperature sensor 32 can be located upstream from the SCR device 30 to monitor the temperature at the inlet of the SCR device 30. An outlet temperature sensor 34 can be located downstream from the SCR device 30 to monitor the temperature at the outlet of the SCR device 30.
The dosing system 16 includes an NH3 tank 38 and a dosing injector 40. The NH3 tank 38 stores a supply of NH3 39. The dosing injector 40 injects the NH3 39 from the NH3 tank 38 into the exhaust gas stream 11. The NH3 mixes with the exhaust gas and serves as a catalyst in concert with the SCR washcoat deposited on the SCR catalyst to decompose the NOx contained in the exhaust gas stream 11. For instance, the mixture of exhaust gas and NH3 chemically reacts with the SCR catalyst to convert NOx into diatomic nitrogen (N2) and water (H2O), thereby reducing the level of NOx emissions.
A PF temperature sensor 46 generates a particulate filter temperature signal that indicates a measured temperature of the PF substrate. Other sensors in the exhaust system 13 may include, for example, an upstream NOx sensor 50 and a downstream NOx sensor 52. The upstream NOx sensor 50 can indicate a level of NOx entering the SCR device 30, while the downstream NOx sensor 52 can be positioned downstream from the PF device 36 to measure a concentration of NOx (e.g., a mass concentration of NOx measured in mass per volume) exiting the PF device 36.
An electronic hardware controller 42 can regulate and control various operations including, but not limited to, the mass flow rate of air delivered to the intake manifold 21 and fuel injection timings of the engine 12. The controller 42 also includes a reductant module 100 that stores various algorithms, models, lookup tables (LUTs), and/or set point values that assist in controlling NH3 injection time and/or NH3 dosing amounts. The controller 42, including the reductant module 100, can be constructed as an electronic hardware controller that includes memory and a processor configured to execute algorithms and computer-readable program instructions stored in the memory.
In at least one embodiment, a sliding mode SCR control system 200 is implemented and is configured to optimize the operating performance of the SCR device 30. The sliding mode control system 200 utilizes various estimates of the actual operating status of the SCR device 30 to reduce, or even prevent, NH3 slippage. The various estimates include, but are not limited to, an estimated amount of NH3 (rRED_ST) actually stored on the SCR catalyst, an estimated NH3 coverage ratio ({circumflex over (R)}) of the SCR catalyst, and an estimated concentration of NH3 slip (ĈNH3) that is present downstream from the PF device 36.
Sensors are not readily available to measure the previously mentioned SCR operating status values. Therefore, the sliding mode SCR control system 200 employs an SCR operating status observer, referred to herein as an SCR status estimator device 102. The SCR status estimator device 102 is in signal communication with the downstream NOx sensor 52 and the controller 42. In at least one embodiment, the SCR status estimator device 102 is constructed as an extended Kalman filter (EKF), for example. Although an EKF is described herein, any type of estimation device may be implemented.
The EKF is an extension of a Kalman filter typically applied to model the behavior of nonlinear systems. For instance, the EKF utilizes a linearized model of an SCR dynamical model to estimate the non-linear behavior of the SCR device 30. The SCR status estimator device 102 may also utilize additional measurement signals to estimate the operating status of the SCR device 30 including, but not limited to, an SCR inlet temperature measured by the inlet temperature sensor 32, an SCR outlet temperature measured by the outlet temperature sensor 34, the mass flowrate of air measured by the MAF sensor 22, the exhaust pressure measured by the pressure sensor 27, the temperature of the exhaust gas measured by the exhaust temperature sensor 31, and the exhaust gas flow rate measured by the exhaust gas flow rate sensor 29.
The reductant module 100 determines a novel NH3 coverage ratio set point (Rsp) associated with the SCR device 30. In at least one embodiment, Rsp is determined by the reductant module 100 using a set point transformation function given by the formula:
where:
F is the exhaust gas mass flow;
ηNOx_sp is a selected target NOx reduction efficiency set point;
Θ is the maximum NH3 storage capacity of the SCR catalyst;
rRED_ST is an estimated amount of NH3 stored on SCR catalyst.
As described herein, “R” is defined as a ratio of stored NH3 with respect to the maximum storage capacity of the SCR catalyst. In other words, “R” indicates the actual NH3 load of the SCR catalyst at a given point in time, with respect to the maximum NH3 storage capacity (Θ) of the SCR catalyst. In at least one embodiment, “R” can be defined as:
Commercial sensors capable of directly measuring R are not readily available. Therefore, the SCR status estimator device 102 can utilize the output of the downstream NOx sensor 52, which indicates a measured concentration of NOx, to output one or more SCR status signals indicating {circumflex over (R)}, and an estimated concentration of NH3 (ĈNH3) present downstream from the SCR device 20. The ĈNH3 can be as a mass concentration of NH3 measured in mass per volume. If the NOx sensor 52 is omitted from the exhaust treatment system 14, the SCR status estimator device 102 can also estimate a concentration of NOx (ĈNOx) that is present downstream from the SCR device 30. The reductant module 100 utilizes the estimated SCR status signals to determine {circumflex over (R)}, and then outputs a control signal that controls the amount of NH3 39 to inject into the exhaust gas stream 11 via the injector 40.
In a non-limiting embodiment, the reductant module 100 controls the dosing system 16 based on {circumflex over (R)} (i.e., the estimate value indicating R) at a given vehicle operating condition. As described herein, R has a mutual correlation with respect to ηNOx. Therefore, Rsp can be selected to achieve a targeted ηNOx as set by ηNOx_SP. maximizing R can improve ηNOx. The reductant module 100 actively computes a control signal (uSMC) that influences the dosing system 16 to inject the correct amount of NH3 into the exhaust gas stream to reach or maintain Rsp. In this manner, the SCR device 30 can be controlled to operate at a targeted ηNOx, which is set by ηNOx_SP, and the amount of NH3 can be actively adjusted so that R is maintained at, or near, Rsp to ensure the SCR device 30 operates at the selected ηNOx_SP. In this manner, the sliding mode SCR control system 200 performs a closed-loop control or feedback control that optimizes the operation of the SCR device 30 and improves overall NOx conversion efficiency.
The reductant module 100 also can determine an appropriate amount of NH3 39 to inject into the exhaust gas stream 11 when a NH3 slip event occurs, without oversaturating the SCR device 30 during NH3 slip conditions. Accordingly, NH3 slip from the SCR device 30 may be reduced, or prevent during a given operating condition of the engine system 10. In at least one non-limiting embodiment, the reductant module 100 utilizes ĈNH3 output by SCR status estimator device 102 to determine or detect a NH3 slip event. When a NH3 slip event is detected, a suitable correction value (uNH3SLIP) is computed and applied to uSMC. Accordingly, uSMC is modified and a control signal (u) is generated that takes into account the slipped NH3 event detected by the reductant module 100. The control signal u is also delivered to the SCR status estimator device 102. Accordingly, the SCR status estimator device 102 can continue determining {circumflex over (R)}, taking into account the slipped NH3 event detected by the reductant module 100.
In another feature, the reductant module 100 may selectively disable the sliding mode SCR control system 200 based on the operating conditions of the engine system 10. For example, the reductant control module can determine when the engine system 10 operates during certain temperatures conditions or ranges that discourage NH3 delivery to the exhaust gas stream due to adverse physical interactions between the NH3 and the SCR catalyst. When these conditions are present, the reductant control module disables the sliding mode SCR control system 200 so that NH3 is not injected into the exhaust gas stream 11.
Turning now to
The memory storage unit 201 stores various algorithms, models, LUTs, and/or set point values utilized to control one or more components of the exhaust treatment system. For example, the memory storage unit 201 stores an NH3 slip threshold value (CNH3_TH) 250, which can be compared against ĈNH3 to detect an NH3 slip event.
The Rsp module 202 is configured to determine Rsp. As described herein, Rsp is selected to reach or maintain a ηNOx_SP corresponding to a target ηNOx of the SCR device. In at least one embodiment, Rsp is computed based on the physical model equation (see Eq. 1) which indicates the R for achieving a target ηNOx with respect to one or more given vehicle operating conditions. The vehicle operating conditions include, but are not limited, engine speed 210, engine load 212, exhaust temperature 214, and SCR temperature 216.
The NH3 SMC module 204 is in signal communication with the Rsp module 202 and the SCR status estimator device 102, and is configured to determine whether R deviates from Rsp. For instance, the NH3 SMC module 204 receives a Rsp signal 256 from the Rsp module 202 indicative of the selected Rsp necessary to reach or maintain ηNOx_SP. The NH3 SMC module 204 also obtains {circumflex over (R)}, ĈNH3, and ĈNOx from an SCR status signal 254 output by the SCR status estimator device 102. Accordingly, the NH3 SMC module 204 computes the correct amount of NH3 to be injected into the exhaust gas stream based on the difference between R (e.g., as indicated by {circumflex over (R)}) and Rsp, and generates uSMC 258 which indicates an amount of NH3 needed reach Rsp or maintain R near Rsp, i.e., within a threshold range of Rsp.
A difference between {circumflex over (R)} and Rsp indicates that R has deviated from the Rsp. In another embodiment, the NH3 SMC module 204 may determine a deviation has occurred when the difference between {circumflex over (R)} and Rsp exceeds a threshold value (RTH). The deviation ultimately affects the amount of injected NH3 that is necessary to maintain the SCR device at the selected ηNOx_SP. When there is a deviation or error between {circumflex over (R)} and Rsp, the NH3 SMC module 204 modifies the uSMC 258 so that the amount of NH3 injected into the exhaust gas stream is adjusted, thereby adjusting R. In at least one embodiment, the NH3 SMC module 204 continuously monitors {circumflex over (R)}, and actively modifies the uSMC 258 to adjust the amount of NH3 injected by the dosing system 16. The active modification of uSMC 258 causes the dosing system 16 to continuously inject more or less NH3 into the exhaust gas stream, which in turn adjusts R. Therefore, R can be returned to Rsp if a deviation occurs.
In another embodiment, the NH3 SMC module 204 determines a change in vehicle operating conditions based on ĈNH3, indicated by the SCR status signal 254, and a concentration of NOx. The concentration of NOx can be a measured value output from the downstream NOx sensor 52 or an estimated value (ĈNOx) indicated by the SCR status signal 254. In response to the changing operating conditions (e.g., when the SCR temperature exceeds a temperature threshold), an updated ηNOx_SP may be determined, and the NH3 SMC module 204 can request a second Rsp (e.g., an updated Rsp) from the Rsp module 202. In this manner, R can be constantly monitored (i.e., as indicated by {circumflex over (R)}) and Rsp can be actively adjusted to achieve a targeted ηNOx at different vehicle operating conditions.
The NH3 slip detection module 206 is configured to detect an NH3 slip event, and to determine a correction value (uNH3SLIP) 252 that modifies uSMC to compensate for the NH3 slip event. In at least one embodiment, the NH3 slip detection module 206 obtains CNH3_TH 250 and determines a concentration of slipped NH3 released from the SCR device. The slipped amount of NH3 can be a measured concentration of slipped NH3 (CNH3) obtained from a NH3 slip sensor (not shown) or can be an estimated concentration of slipped NH3 (ĈNH3) obtained from the SCR status signal 254. In one or more embodiments, the value ĈNH3 is estimated based on the concentration of NOx output from the downstream NOx sensor 52, along with additional measured values including, but not limited to, the SCR inlet temperature measured by the inlet temperature sensor 32, and the SCR outlet temperature measured by the outlet temperature sensor 34.
A NH3 slip event can be detected when CNH3 or ĈNH3 exceeds CNH3_TH. In at least one embodiment, the NH3 slip module 206 determines uNH3SLIP based on the following equation:
uNH3SLIP=kp·eNH3+kiSNH3, [Eq. 3]
The NH3 calculator module 208 combines uSMC 258 and uNH3SLIP 252, and scales the combined value to obtain u, which indicates the amount of NH3 injected into the exhaust gas stream. In at least one embodiment, the NH3 calculator module 208 generates an NH3 control signal 260 indicative of u, which controls the amount of NH3 to be injected by the dosing system 16 to maintain Rsp. In at least one embodiment, u, as indicated by the NH3 control signal 260, is represented by the expression:
u=G(uSMC+uNH3SLIP), where G is a scaling factor [Eq. 4]
The scaling factor (G) is utilized to transform u having measured units of grams per second (g/s) into an equivalent NH3 control signal having measured units of milligrams per second (mg/s).
Accordingly, the reductant module 100 can compute Rsp as a function of ηNOx. Thus, a target ηNOx at a given vehicle operating condition can be set according to ηNOx_sp. The reductant module 100 can actively monitor R, and (recognizing the mutual correlation between R and ηNOx) compute the necessary Rsp to achieve the ηNOx_sp while taking into account changes in vehicle operating conditions.
Turning now to
When, however, the sliding mode SCR control system 200 is enabled at operation 302, the method proceeds to operation 306 such that a ηNOx_SP corresponding to a target a target ηNOx is determined, and estimated measurements (e.g., {circumflex over (R)}, ĈNH3, ĈNOx, etc.) output from the SCR status estimator device 102. At operation 308, Rsp for achieving ηNOx_SP is determined. In at least one embodiment, Rsp is determined based on ηNOx_SP. At operation 310, uSMC is computed and a control signal for controlling the dosing system 16 is generated based on uSMC. The value uSMC can be computed based on ĈNH3, ĈNOx, {circumflex over (R)}, and Rsp, and which can be estimated using the SCR status estimator device 102. Additional measured values such as, for example, exhaust gas flow rate through the SCR device 30, SCR catalyst temperatures, etc., can also be utilized to assist in determining uSMC. As vehicle operating conditions change, R is monitored based on {circumflex over (R)}. Accordingly, the amount of NH3 is actively adjusted so that the R reaches Rsp, or is maintained at the selected Rsp, to achieve or maintain a selected ηNOx_SP.
At operation 312, an NH3 slip detection process is performed. When an amount of slipped NH3 is below CNH3_TH, or if no NH3 slip is detected, uNH3SLIP is set to zero “0” or can even be set at a negative value at operation 314 indicating that a correction of uSMC is unnecessary. At operation 316, the control signal u is generated. In at least one embodiment, u is based on a summation (uSMC+uNH3SLIP). Thus, when uNH3SLIP is set to zero “0”, for example, u is generated as an un-modified control signal based on uSMC. After generating u, the method returns to operation 300 and the operations described above are repeated.
When, however, NH3 slip is detected at operation 312, uNH3SLIP is set to a value proportional to the concentration of NH3 that has slipped from the SCR device 30 at operation 318. Accordingly, uNH3SLIP is added to uSMC at operation 316 such that u is generated to compensate for the slipped NH3. The method returns to operation 300 and the operations described above are repeated.
Various non-limiting embodiments described herein provide a sliding mode SCR control system 200 that optimizes the operating performance of the SCR device 30. The system 200 includes a reductant module 100 that computes a novel set point referred to as an NH3 coverage ratio set point (Rsp). The Rsp value is computed as a function of a target NOx reduction efficiency (ηNOx) corresponding to the SCR device 30. Thus, a target ηNOx for a given vehicle operating condition can be set using a ηNOx set point (ηNOx_sp), and the {circumflex over (R)} can be actively monitored to determine whether the actual R associated with the SCR device has deviated from Rsp. The reductant module 100 controls a dosing system 16 to inject the correct amount of NH3 into the exhaust gas stream to maintain R at Rsp, or near Rsp, thereby operating the SCR device 30 at ηNOx_sp while taking into account changing operating conditions of the vehicle.
While the above disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from its scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiments disclosed, but will include all embodiments falling within the scope thereof.
| Number | Name | Date | Kind |
|---|---|---|---|
| 20120255286 | Matsunaga | Oct 2012 | A1 |
| 20130232958 | Ancimer | Sep 2013 | A1 |
| 20140033683 | Wei | Feb 2014 | A1 |
| 20160326928 | Osburn | Nov 2016 | A1 |
| 20170044953 | Shinoda | Feb 2017 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20180306082 A1 | Oct 2018 | US |
