Abstract:
A system for reducing environmentally harmful emissions from an internal combustion engine. The system may incorporate an exhaust after-treatment device. The exhaust after-treatment device may use selective catalytic reduction to remove certain emissions from the exhaust of the engine. Urea solution may be inserted into the exhaust emissions, which is decomposed to ammonia to become a reduction agent for reduction of NOx in the emissions. The engine may be managed by a controller and the exhaust after-treatment device may be managed by another controller. These controllers may be cascaded, or be managed by a third controller that provides hierarchical or coordinated control of engine performance and emissions reduction. The engine and the exhaust after-treatment device may be modeled to aid in designing and building a system for coordinated control of an actual engine and a selective catalytic reduction after-treatment device. The controllers may be predictive model controllers.

Description:
BACKGROUND 
       [0001]    The present disclosure pertains to environmentally harmful emissions and particularly to an approach to reduce such emissions from internal combustion engines. 
       SUMMARY 
       [0002]    The disclosure reveals a system for reducing environmentally harmful emissions from an internal combustion engine. The system may incorporate an exhaust after-treatment device. The exhaust after-treatment device may use selective catalytic reduction to remove certain emissions from the exhaust of the engine. Urea solution may be inserted into the exhaust emissions, which is decomposed to ammonia to become a reduction agent for reduction of NOx in the emissions. The engine may be managed by a controller and the exhaust after-treatment device may be managed by another controller. These controllers may be cascaded, or be managed by a third controller that provides hierarchical or central coordinated control of engine performance and emissions reduction. The engine and the exhaust after-treatment device may be modeled to aid in designing and building a system for coordinated control of an actual engine and a selective catalytic reduction after-treatment device. The controllers may be predictive model controllers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1  is a diagram of a basic engine plant system; 
           [0004]      FIG. 2  is a diagram of a basic engine arrangement with control but no selective catalyst reduction; 
           [0005]      FIG. 3  is a diagram of a combined engine and selective catalyst reduction system; 
           [0006]      FIG. 4  is a diagram of an uncoordinated engine and selective catalyst reduction control system; 
           [0007]      FIG. 5  is a diagram of a system having cascaded coordinated control; and 
           [0008]      FIG. 6  is a diagram of a hierarchical coordinated control system. 
       
    
    
     DESCRIPTION 
       [0009]    Due to ongoing emissions legislation in many geographical regions, and for many applications, many diesel engines need to significantly limit the NOx emissions from the tailpipe. Selective catalytic reduction (SCR) may involve a NOx after-treatment device that actively injects urea solution into the exhaust stream which may decompose to ammonia for a catalyzed chemical reaction. However, control strategies need to be coordinated in order to achieve the maximum achievable performance—in terms of NOx emissions and vehicle fuel economy. 
         [0010]    The present approach may coordinate the control of the engine and SCR device. Coordinated control of these two subcomponents may lead to very much reduced NOx emissions to meet strict clean air regulations and also improved vehicle fuel efficiency. 
         [0011]    When two devices, an engine and an aftertreatment mechanism, are controlled independently, an engine control system may simply and generally always try to reduce the engine-out NOx as much as possible. This may often be done by a massive exhaust gas recirculation which is not necessarily optimal for soot emissions and fuel efficiency. It may often be thought, from an overall optimality point of view, that the engine control system rely on the aftertreatment mechanism to reduce NOx emissions. Instead, the engine control system should control the aftertreatment temperature to maximize its efficiency. This may be achieved virtually only by coordinated control. 
         [0012]    The present approach may utilize modeling and control technology. First, models of the engine and after-treatment subsystems may be created. The models of the engine and exhaust after-treatment subsystems may track actual engine and exhaust after-treatment subsystems. From these models one or more multivariable controllers may be synthesized. A multi-variable controller may address the inherent interactions of an overall coordinated engine-SCR control system. 
         [0013]    The present description may treat the models of the engine and exhaust after-treatment subsystems as actual subsystems. 
         [0014]    A series of  FIGS. 1-4  indicate some basic elements of an engine and emission control approaches which lead up to  FIGS. 5 and 6  which show examples of the present system.  FIG. 1  is a diagram of a basic engine plant model system  10 . Input  12  (w eng ) may incorporate detected engine speed, fueling rate, ambient conditions, such as temperature and air pressure, and so on. Input  13  (u eng ) may incorporate signals to actuators on the engine (e.g., variable geometry turbine (VGT), exhaust gas recirculation (EGR), throttles, fuel injection specifications, variable valve actuation (VVA), and so on). “u eng ” may be regarded as one or more engine actuators. There may be a block (G eng )  11  representing an engine plant model, such as a diesel engine with a turbocharger. An output  14  may be based on SFC (specific fuel consumption, for instance, in grams per kilowatt hour) of the engine. An output  15  may indicate a PM (particulate matter) output of the engine and output  17  may indicate a NOx eng  (i.e., nitrogen oxides) output of the engine. NOx may be measured in parts per million. 
         [0015]      FIG. 2  is a diagram of a basic engine arrangement  18  with control but no SCR. There may be a feedback  19  (y eng ) (engine sensors) from G eng    11  to a K eng  block  21  which may represent an embedded computer. y eng    19  may incorporate signals from sensors for MAP, EGR flow, temperatures, NOx emissions, and so on. K eng  controller  21  may incorporate one or more control algorithms. A signal  19  may represent the on-engine measurements. “y eng ” may be regarded as engine sensors. A control goal may be to control the various actuators to achieve engine specific goals such as tracking desired boost pressures, fresh and/or mass air flow, EGR flow, and so forth, and indirectly be responsible for providing trade offs among SFC, PM and NOx, and other items. Often a control goal may be to minimize SFC such that legal constraints on PM and NOx are satisfied. U eng    13  (engine actuators) may incorporate actuator signals from K eng  controller  21  to G eng  block  11 . 
         [0016]      FIG. 3  is a diagram of a combined engine and SCR plant system  23 . With an addition of an SCR after-treatment device  24  to the basic engine plant model  11 , one may change the NOx component of the engine outputs by adding an ammonia component (NH3). There may be a w eng  input  12  and a u eng  input  13  to engine (G eng ) block  11 . The performance may in part be defined by SFC  14  and PM  15  from the G eng  block  11 . A signal  17  representing or indicating NOx eng , T exh  (exhaust temperature) and m exh  (exhaust mass) may proceed from the G block  11  to an SOP after-treatment (G) device  24 . The T exh  may be determined before an entry of the exhaust to device  24 . System  23  may provide a u urea  input signal  25  to G scr  device block  24 . “u uera ” may be regarded as a urea solution dosing actuator. Block  24  may have an output  26  of NOx scr  and an output  27  of NH3 scr . Outputs  26  and  27  are the items of the system that may need to meet legal requirements relating to exhaust NOx emissions. 
         [0017]    A time constant may be associated with the engine in block  11  and with the SCR device in block  24 . The time constant of block  11  may be an amount of time (e.g., about 1-2 seconds) that is needed for changed inputs to block  11  to result in a certain amount (e.g., 63 percent) of stabilization of the response of the system to the inputs. The time constant of block  24  may be an amount of time (e.g., about 20-30 seconds) that the after-treatment device needs because of a temperature change caused by a change of inputs resulting in a change of exhaust. 
         [0018]    Relative to the SCR device, a catalyst may be a part of the device (usually contained in a wash coat). What is injected to the exhaust gas may be a urea solution which is decomposed to ammonia and the ammonia is used as reduction agent for various chemical reactions (e.g., NOx reduction). Ammonia is adsorbed on the catalyst (e.g., a catalyst of a platinum-zeolite type) 
         [0019]      FIG. 4  is a diagram of an uncoordinated engine and SCR control system  28 , having portions of system  18  of  FIG. 2  and system  24  of  FIG. 3 , and additionally a K block  31  in a feedback loop of G scr  block  24  with a y scr  signal  29  (SCR sensors) from G scr  block  24  or after-treatment mechanism  24  to a K scr  or controller block  31  and a u urea  signal  25  input from controller block  31  to the G scr  block  4  for controlling an amount of urea solution injected into the engine exhaust  17  in the after-treatment mechanism  24 . “y scr ” may be regarded as SCR sensors. Such SCR sensors may be for upstream NOx (engine-out NOx), downstream NOx (tailpipe-out NOx), downstream NH3, upstream/downstream temperatures, exhaust flow, and the like. Techniques for SCR control may have the K scr    31  act on information y scr    29  of the state of the exhaust  17  entering the G scr    24  or SCR device  24 . The state of the exhaust entering device  24  may be some combination of NOx, T exh  and/or m exh . A state of the exhaust that is leaving the SCR device  24  may be some combination of NOx and/or NH3. 
         [0020]    Looking at the “combined engine-SCR plant”, a centralized MIMO controller appears to be a possible option. However, a dramatic difference in bandwidths (i.e., time constants of G eng  block  11  and G scr  block  24 ) may be a challenge, which suggests that a separated structure might be more practical. Generally, the SCR device  24  may decrease the engine out NOx, which could mean that there is extra capability in the engine controller K eng    21  to optimize the other items. Here, one may have a tradeoff where there is a making NOx eng  higher to achieve a better SFC or vice versa. 
         [0021]    The performance of the SCR device  24  may be governed by the urea solution dosing and also the properties of NOx  eng  (NOx concentration of exhaust gas), T exh  (temperature of exhaust gas), and m exh  (mass flow of exhaust gas) which influence the SCR device&#39;s states (temperature and NH3 coverage). The engine variables in turn may vary as a function of engine speed and fuel, ambient conditions, and engine actuators, which change much faster than a 20-30 second time constant of the G scr  or SCR  24 . The actuators relative to u eng  may be responsible for governing engine functions in order to manipulate engine performance factors such as SFC and PM in addition to managing the SCR relevant variables of NOx eng , T exh , and m exh . 
         [0022]    So it seems that the NOx eng , T exh , m exh  might be coordinated with a urea solution dosing to enhance the overall performance of the engine-SCR system  28 , but one may need to carefully consider what aspects of the control to focus on. That is, one cannot necessarily expect to be able to hold NOx eng , T exh , and m exh  at a desired setpoint for a very long time considering the dynamic needs of SCR  24  and the fact that the engine actuators of G eng    11  or engine plant model  11  also have to deliver engine performance. 
         [0023]      FIG. 5  is a diagram of a system  34  with cascaded coordinated control which may be considered. Cascading controllers  31  and  21  may be a part of the system&#39;s control strategy. Implicit in controller  31  may be a supervisory controller. A w eng  signal  12  may enter a K scr  controller block  31  and a G eng  engine block  11 . A r eng  signal  36  may go from the K scr  block  31  to the K eng  block  21 . A u eng  signal  13  for engine actuators may go from the K eng  block.  21  to the G eng  block  11 . A signal y eng    19  from engine sensors may have information fed back from the G eng  block  11  to the K eng  block  21 . An output SFC signal  14  and a PM signal  15  may be output from the G eng  block  11 . A directly or indirectly measured NOx eng , T exh , m exh  signal  17  may go from the G eng  block  11  to a G scr  block  24 . The K scr  block  31  may provide an output signal u urea    25  signal (actuator) for indicating an amount of urea solution to be injected into the SCR device G scr  block  24 . The G scr  block  24  may feed back a y scr  signal  29  with SCR sensor information about G scr    24  to the K scr  block  31  for modification of setpoints, input parameters, speed, fuel, and so on, of the engine as indicated by w eng    12 . The SCR device (G scr  block  24 ) may output a NOx scr  signal  26  and an NH3 scr  signal  27 . 
         [0024]    The r eng  signal  36  may refer to the setpoints and input parameters for the engine controller (K eng )  21 . The SCR controller (K scr )  31  may use the r eng  signal  36  for actuation to assist in the SCR  24  control via the NOx eng , T exh  and m exh  signal  17 . 
         [0025]    K eng  block  21  and/or K scr  block  31  may each represent a model predictive control (MPC) controller. If one assumes that K scr  block  31  represents an MPC controller, then one may put constraints on the r eng  signal  36  so that engine control goals, such as, for example, requirements on PM, SFC and NOx eng , are respected. The present structure  34  may permit a use of the r eng  signal  36  to enhance a slow transient response of the K scr  block  31 . 
         [0026]      FIG. 6  is a diagram of a hierarchical coordinated control system  38 . A w eng  signal  12  may enter a K block  39  and a G eng  block  11 . A r eng  signal  36  may go from the K block  39  to a K eng  block  21 . A u eng  signal  13  may go from the K eng  block  21  to the G eng  block  11 . A y eng  signal  19  may be fed back from the G eng  block  11  to the K eng  block  21 . An output of the engine may include SFC  14  and a PM signal  15  as output from the G eng  block  11 . A NOx eng , T exh  and m exh  signal  17  may go from the G eng  block  11  to a G scr  block  24 . An r scr  signal  41  may go from the K block  39  to a K scr  block  31 . A u urea  signal  25  may go from the K scr  block  31  to the G scr  block  24 . Outputs from the SCR device G scr  block  24  may include a NOx scr  signal  26  and an NH3 scr  signal  27 . 
         [0027]    The control strategy for system  38  of  FIG. 6  may have a hierarchical structure with the controller K scr    31  dedicated to the G scr    24 . Here, the K block  39  may be a supervisor controller or coordinator which manipulates the setpoints w eng , r eng , r scr  and so on for the local controllers K eng    21  and K scr    31 , so that the prescribed goals are achieved, i.e., namely, the requirements for NOx scr , NH3 scr , PM, SFC, and so forth. K block  39 , K eng  block  21  and/or K scr  block  31  may each represent an MPC controller. 
         [0028]    Model predictive control (MPC) is a control approach that appears to have been successfully applied in many industrial control applications. MPC appears suitable for applications where it may be necessary dynamically coordinate several actuators to drive several controlled variables. Such systems may be known as multivariable. MPC appears able to include constraints on various signals in a control loop systematically. The ability to handle the constrained multivariable dynamical system in a systematic way may be the key factor which increases popularity of MPC. 
         [0029]    MPC may use a dynamical model of the controlled system to predict future behavior of a controlled technology or process. Based on this prediction and based on defined optimality criteria, MPC may compute an optimal control signal by solving a constrained optimization problem. This optimization problem should be solved at each sampling period to reject the disturbances and to ensure certain degree of robustness. An example of such optimization problem is expression (1). 
         [0000]        Uopt =arg min  J ( U,x,p )  s.t. g ( U,x,p )&lt;=0   (1)
 
         [0000]    In expression (1), Uopt is the optimal control signal trajectory, J(U,x,p) is MPC cost function, g(U,x,p) represents MPC constraints, U is the optimization variable, x may be the internal state of the controlled system and p may represent various parameters. The cost function J(U,x,p) may be a weighted sum of various penalties, for example, a sum of squared 2nd norms of tracking error over the prediction horizon, sum of squared 2nd norms of actuator movements, and so on. Constraints g(U,x,p) may include limits for actuators and for various controlled variables over the prediction horizon. 
         [0030]    The efficiency of the solver appears as a key factor limiting range of applications with fast sampling periods (in combination with performance of computation environment), e.g., automotive applications. Recent development of solvers for a fast MPC may enable an application of MPC technology for relatively fast automotive systems, for example, an engine air path or emissions control as it is briefly described herein. Suitable solvers for fast MPC may be based on an on-line solution or explicit solution of a parametric optimization problem (1). To achieve the best efficiency, the solvers for MPC may be standard, directly tailored for MPC or directly tailored for a particular MPC application. The on-line solvers may be based on active set (standard formulation, gradient projection, and so forth), interior point, and so on. The explicit solution may be based on multi-parametric approach, primal-dual feasibility approach, and so on. 
         [0031]    An uncoordinated MPC control may be illustrated by the control structure shown in  FIG. 4  (block or system  28 ). One or both controllers  21  and  31  may be implemented as an MPC. The objective of engine air path controller K eng    21  is to ensure that the selected controlled variables will follow their setpoints while all given constraints will be satisfied. The controlled variables  19  (engine sensors) may be, for example, any combination from the following set: boost pressure, exhaust gas recirculation flow, lambda sensor, exhaust manifold pressure, total engine air flow, turbocharger speed, and so on. The engine actuators  13  may be exhaust gas recirculation valve, turbocharger actuator, wastegate valve, throttle valve, start of injection, and so forth. The considered constraints may be, for example, upper and lower limits of actuator positions, a limit for lambda sensor, a limit for turbocharger speed, and so on. An objective for the controller K scr    31  is to control tailpipe emissions. A manipulated variable for K scr    31  may be an amount of injected urea solution  25  to the engine exhaust gas stream. Controlled variables  29  (SCR sensors) may be tailpipe emissions, namely NOx concentration  26 , and PM and ammonia slip  27 . 
         [0032]    A cascaded coordinated MPC control may be illustrated structure or system  34  shown by  FIG. 5 . The structure may reflect the fact that the SCR system  24  is much slower that the engine air path. Therefore, it may be beneficial to configure two MPC controllers  21  and  31  in the cascade structure  34 . The engine controller (K eng )  21  may be configured to ensure basic stability of the engine air path. The additional degrees of freedom of controller  21  may be then used to influence engine exhaust gas properties so that the downstream SCR device  24  can work effectively. Controlled variables (y eng )  19  (engine sensors) of K eng  controller  21  may be the same as those in the uncoordinated case but it may be beneficial to add other controlled variables  17  (after-treatment sensors) which are directly related to SCR device operation and can be influenced by the engine actuators, i.e., NOx concentration and exhaust gas temperature. The SCR controller (K scr )  31  may be configured as a coordinator of K eng  controller  21 . K scr  controller  31  may be slower than K eng  controller  21  and may provide setpoints  36  for K eng  controller  21  to ensure efficient operation (NOx conversion) of SCR device  24 . The controlled variables (y scr )  29  (SCR sensors) of K scr  controller  31  may be the same as those in the uncoordinated case, i.e., NOx concentration  26  and ammonia slip  27 . The manipulated variable may be an amount of injected urea solution  25  but also a selected subset of setpoints  36  for K eng  controller  21 , e.g., engine exhaust NOx concentration  17  setpoint and engine exhaust gas temperature  17  setpoint. 
         [0033]    The configuration, structure or system  38  is shown in  FIG. 6 . Control structure  38  may combine uncoordinated MPC control and cascade coordinated control. There may be two local controllers K eng    21  and K scr    31 . Controllers K eng    21  and K scr    31  may be coordinated by a central coordinator or controller K  39 . One, two or three of the controllers  21 ,  31  and  39  may be MPC controllers. The control or actuators (u eng )  13  and controlled variables (y eng )  19  (engine sensors) of K eng  controller  21  may be the same as those in cascaded coordinated MPC control. The r eng  setpoints  36  for the controlled y eng  signals  19  (engine sensors) may be computed by controller or coordinator K  39 . A manipulated variable of controller K scr    31  may be an amount of injected urea solution (u urea )  25 . The controlled variables (y scr )  29  (SCR sensors) of K scr  controller  31  may be NOx emissions  26  and NH3 slip  27 . Setpoints (r scr )  41  for the controlled variables  29  may be computed by coordinator K  39 . Coordinator K  39  may be configured so that the overall efficiency of both engine and SCR device are maximized while minimizing the operation costs. 
         [0034]    A recap in view of  FIGS. 1-6  may be noted. A selective catalytic reduction control system may incorporate a diesel engine or a model of the engine, a selective catalytic reduction exhaust after-treatment mechanism for connection to the engine, an engine controller, and a selective catalytic reduction controller connected to the selective catalytic reduction exhaust after-treatment mechanism and to the engine controller. The engine controller and the selective catalytic reduction controller may provide coordinated control of the engine and selective catalytic reduction selective catalytic reduction exhaust after-treatment mechanism to control an amount of pollutants in an exhaust emission from the engine. The items noted herein may be modeled. 
         [0035]    The engine controller and the selective catalytic reduction controller may provide coordinated control of the engine and selective catalytic reduction exhaust after-treatment mechanism to optimize selective catalytic reduction of pollutants in the exhaust emission so as to reduce specific fuel consumption and/or particulate matter emission. The engine controller and the selective catalytic reduction controller may be model predictive controllers. 
         [0036]    The selective catalytic reduction exhaust after-treatment mechanism may provide a catalyst into the exhaust emission for selective catalytic reduction of the pollutants in the exhaust emission. The pollutants may have NOx. The selective catalytic reduction may incorporate reducing NOx in the exhaust emission. 
         [0037]    An amount of urea solution, which may be decomposed to ammonia injected into the exhaust emission, may be determined by a signal from the selective catalytic reduction controller. The signal may determine the amount of urea solution according to information about the pollutants in the exhaust emission. Information about the pollutants may have an indication of magnitude of NOx in the exhaust emission. 
         [0038]    An output signal may be provided by the selective catalytic reduction controller to the engine controller. The output signal may be for indicating the information about the exhaust. The information about the exhaust may incorporate indicating an amount of NOx in the exhaust emission, exhaust mass and/or a temperature of the exhaust. 
         [0039]    An approach for selective catalytic reduction, may incorporate providing a first model of a diesel engine and associated components, a second model of an exhaust after-treatment device coupled to an exhaust of the first model of the diesel engine, an engine controller connected to the first model of the diesel engine, and a selective catalytic reduction controller connected to the second model of the exhaust after-treatment device. The approach may also incorporate simulating a treating an exhaust of the first model with selective catalytic reduction as provided by the second model to reduce pollutants in the exhaust, simulating an operation of the first model to increase fuel efficiency, and coordinating the first and second models in conjunction with the first and second controllers, respectively, to allow for a reduction of pollutants and an increase the fuel efficiency. The controllers may be model predictive controllers. 
         [0040]    A selective catalytic reduction of pollutants may incorporate injecting a prescribed amount of urea solution into the exhaust. The prescribed amount of urea solution may be determined by coordinated control of the first and second models and the selective catalytic reduction to allow for the reduction of pollutants such as NOx, and increased fuel efficiency of the engine. 
         [0041]    The approach may further incorporate obtaining information about a reduction of the amount of NOx with ammonia decomposed from the urea solution. The amount of urea solution provided to the exhaust may be prescribed according to the information about the reduction of NOx with ammonia decomposed from the urea solution. 
         [0042]    An engine emissions reduction system may incorporate an exhaust after-treatment device, and a system controller connected to the exhaust after-treatment device. The exhaust after-treatment device may incorporate a coupling for connection to an exhaust of a diesel engine. The system controller may be connected to the engine and to the exhaust after-treatment device. The system controller may coordinate control of the engine and the exhaust after-treatment device to provide selective catalytic reduction of polluting emissions from the engine. 
         [0043]    The system controller may incorporate a supervisory controller, an engine controller connected to the supervisory controller and the engine, and a selective catalytic reduction controller connected to the supervisory controller and the exhaust after-treatment device. The system controller may coordinate control of the engine, and the exhaust after-treatment device to further provide increased fuel efficiency of the engine. The polluting emissions may have NOx. The selective catalytic reduction may neutralize the NOx with an addition of urea solution to the emissions. 
         [0044]    The controllers may be model predictive controllers. The selective catalytic reduction controller may provide a signal indicating an amount of urea solution to be provided to the polluting emissions. The signal may be conveyed to the exhaust after-treatment device for releasing the amount of urea solution into the polluting emissions exhaust of the engine. At an exhaust output downstream from the exhaust after-treatment device, the amount of urea solution released into the exhaust may be determined by the signal from the selective catalyst reduction controller that indicates the amounts of NOx and NH3 in the exhaust and amounts of NOx and NH3 permitted in the exhaust by applicable regulations on emissions. 
         [0045]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0046]    Although the present system and/or approach has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the related art to include all such variations and modifications.