CONTROL APPARATUS AND METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE

Abstract

An exhaust gas after-treatment system for an internal combustion engine includes a selective catalyst reduction on filter (SCRF) exhaust gas after-treatment device in communication with exhaust gases from the internal combustion engine and having treated exhaust gas output. An oxides of nitrogen (NOx) sensor is coupled to treated exhaust gases and has a NOx sensor output signal that is NOx and ammonia (NH.sub.3) cross-sensitive. A closed loop observer (CLO) is operatively coupled to receive the NOx sensor output signal and provides a NOx concentration signal to an electronic control unit operatively associated with the exhaust gas after-treatment system and the internal combustion engine. CLO output at least includes an exhaust gas NOx concentration estimate and the ECU is arranged to be operable upon the NOx concentration estimate to control exhaust gas after-treatment system and internal combustion engine to effect an overall reduction in actual NOx concentration with the exhaust gases.

Claims

1. An exhaust gas after-treatment system for an internal combustion engine having a diesel exhaust fluid (DEF) system and a selective catalyst reduction filter (SCRF), the exhaust gas after-treatment system comprising: a SCRF exhaust gas after-treatment device in communication with a source of exhaust gases and having a treated exhaust gas output; an oxides of nitrogen (NOx) sensor coupled to the treated exhaust gas output, the NOx sensor having a NOx sensor output signal that is NOx and ammonia (NH.sub.3) cross-sensitive; a closed loop observer (CLO) operatively coupled to receive the NOx sensor output signal and to provide a CLO output signal to an electronic control unit (ECU) that is operatively associated with the exhaust gas after-treatment system and the internal combustion engine, the ECU comprising a first controller having a first microprocessor, the first microprocessor comprising a first program stored therein, the CLO comprising a second controller having a second microprocessor, the second microprocessor comprising a second program stored therein, wherein the CLO output signal at least includes an exhaust gas NOx concentration estimate and the ECU is programmed to provide the SCRF exhaust gas after-treatment device a DEF injection signal for the DEF system to inject a measured quantity of DEF into the exhaust gases upstream the SCRF to effect an overall reduction in actual NOx concentration with the exhaust gases, wherein the CLO output signal at least includes an NH3 storage estimate into the SCRF, the NH3 storage being estimated when an NH3 slip evident condition is verified by comparing NOx sensor readings and when a linearized model is coherent with the NH3 slip evident condition.

2. The exhaust gas after-treatment system of claim 1, wherein the NH3 storage is estimated when urea injection into the SCRF at least once in a time window is verified and when NOx sensor readings are below sensor accuracy.

3. The exhaust gas after-treatment system of claim 1, wherein the NH3 storage estimate comprises: an adjusted output matrix of discrete-time linearized model; an adjusted NOx sensor measurement as: NOxSnsr2_new_measure=NOxSnsr2_real_measure/cross_sensitivity_factor; and an adjusted NOx sensor estimation as: NOxSnsr_estimation=NH3_only_estimation.

4. The exhaust gas after-treatment system of claim 1, wherein the CLO comprises a selective catalyst reduction (SCR) model, the SCR model being configured to provide an estimated ammonia NH.sub.3 concentration within the exhaust gases.

5. The exhaust gas after-treatment system of claim 4, wherein the CLO comprises a filter, the filter being configured to provide at least one parameter value to the SCR model.

6. The exhaust gas after-treatment system of claim 1, wherein the CLO comprises a NOx sensor model, the NOx sensor model being configured to provide the NOx concentration estimate.

7. The exhaust gas after-treatment system of claim 6, wherein the CLO comprises a filter, the filter being configured to provide at least one parameter value to the NOx sensor model.

8. The exhaust gas after-treatment system of claim 1, wherein each of the CLO and the ECU are operatively coupled to receive an operating parameter of the internal combustion engine, wherein the CLO and the ECU are further arranged to be operable upon the operating parameter to control the exhaust gas after-treatment system and the internal combustion engine to effect an overall reduction in actual NOx concentration with the exhaust gases.

9. A vehicle comprising an exhaust gas after-treatment system in accordance with claim 1.

10. A controller for a vehicle internal combustion engine exhaust gas after-treatment system, the internal combustion engine having a diesel exhaust fluid (DEF) system and a selective catalyst reduction filter (SCRF), the exhaust gas treatment system including a SCRF exhaust gas after-treatment device in communication with exhaust gases from the internal combustion engine and having a treated exhaust gas output, an oxides of nitrogen (NOx) sensor coupled to the treated exhaust gas output, the NOx sensor having a NOx sensor output signal that is NOx and ammonia (NH.sub.3) cross-sensitive, and an electronic control unit (ECU) operatively coupled to the internal combustion engine and the exhaust gas after-treatment system, the controller comprising: a closed loop observer (CLO) operatively coupled to receive the NOx sensor output signal and to provide a CLO output signal to the ECU, the ECU comprising a first controller having a first microprocessor, the first microprocessor comprising a first program stored therein, the CLO comprising a second controller having a second microprocessor, the second microprocessor comprising a second program stored therein wherein the CLO output signal at least includes an exhaust gas NOx concentration estimate and the ECU is programmed to provide the SCRF exhaust gas after-treatment device a DEF injection signal for the DEF system to inject a measured quantity of DEF into the exhaust gases upstream the SCRF to effect an overall reduction in actual NOx concentration with the exhaust gases, wherein the CLO output signal at least includes an NH3 storage estimate of the SCRF when an NH3 slip evident condition is verified and when a linearized model is coherent with the NH3 slip evident condition.

11. The controller of claim 10, wherein the CLO output further comprises an ammonia coverage ratio representing a quantity of ammonia stored within the SCRF device.

12. The controller of claim 10, wherein the CLO output further comprises an estimated ammonia NH.sub.3 concentration within the exhaust gases.

13. The controller of claim 10, wherein the CLO comprise a selective catalyst reduction (SCR) model, the SCR model being configured to provide an estimated ammonia NH.sub.3 concentration within the exhaust gases.

14. The controller of claim 13, wherein the CLO comprises a filter, the filter being configured to provide at least one parameter value to the SCR model.

15. The controller of claim 10, wherein the CLO comprises a NOx sensor model, the NOx sensor model being configured to provide the NOx concentration estimate.

16. The controller of claim 15, wherein the CLO comprises a filter, the filter being configured to provide at least one parameter value to the NOx sensor model.

17. A method of controlling a vehicle internal combustion engine exhaust gas after-treatment system, the internal combustion engine having a diesel exhaust fluid (DEF) system and a selective catalyst reduction filter (SCRF), the exhaust gas treatment system including a SCRF exhaust gas after-treatment device in communication with exhaust gases from the internal combustion engine and having a treated exhaust gas output, an oxides of nitrogen (NOx) sensor coupled to the treated exhaust gas output, the NOx sensor having a NOx sensor output signal that is NOx and ammonia (NH.sub.3) cross-sensitive, and an electronic control unit (ECU) operatively coupled to the internal combustion engine and the exhaust gas after-treatment system, the method comprising: providing via a closed loop observer (CLO) operatively coupled to receive the NOx sensor output signal an exhaust gas NOx concentration estimate to the ECU, the ECU comprising a first controller having a first microprocessor, the first microprocessor comprising a first program stored therein, the CLO comprising a second controller having a second microprocessor, the second microprocessor comprising a second program stored therein, the ECU being programmed to provide the SCRF exhaust gas after-treatment device a DEF injection signal for the DEF system to inject a measured quantity of DEF into the exhaust gases upstream the SCRF; and injecting the measured quantity of DEF into the exhaust gases upstream the SCRF to effect an overall reduction in actual NOx concentration with the exhaust gases responsive to the NOx concentration estimate, wherein the CLO output signal at least includes an NH3 storage estimate of the SCRF when an NH3 slip evident condition is verified and when a linearized model is coherent with the NH3 slip evident condition.

18. The method of claim 17, wherein providing via a CLO an exhaust gas NOx concentration estimate further comprises: providing an estimated ammonia (NH.sub.3) concentration within the exhaust gases, and controlling the exhaust gas after-treatment system and the internal combustion engine to effect an overall reduction in actual NOx concentration with the exhaust gases responsive to the NOx concentration estimate and the estimated NH.sub.3 concentration.

19. The method of claim 17, wherein providing via a CLO an exhaust gas NOx concentration estimate further comprises providing an ammonia coverage ratio, and controlling the exhaust gas after-treatment system and the internal combustion engine to effect an overall reduction in actual NOx concentration with the exhaust gases responsive to the NOx concentration estimate and the ammonia coverage ratio.

20. The method of claim 17, further comprising providing at least one internal combustion engine operating parameter to the ECU and controlling the exhaust gas after-treatment system and the internal combustion engine to effect an overall reduction in actual NOx concentration with the exhaust gases responsive to the NOx concentration estimate and the at least one internal combustion engine operating parameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements.

[0028] FIG. 1 is a schematic representation of a vehicle incorporating an after-treatment system applied to an internal combustion engine that is operable in accordance with the herein described embodiments;

[0029] FIG. 2 is a block diagram illustration of an after-treatment system in accordance with the herein described embodiments; and

[0030] FIG. 3 is a block diagram illustration of a NOx sensor operable within an after-treatment system in accordance with the herein described embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS

[0031] The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. Exemplary embodiments will now be described with reference to the drawings, wherein conventional or commonly known elements may be omitted for clarity.

[0032] Some embodiments may include an automotive system 10, which as shown in FIG. 1 includes an internal combustion engine (ICE) 12 of conventional construction including an engine block defining at least one cylinder having a piston coupled to rotate a crankshaft. A cylinder head cooperates with the piston to define a combustion chamber. A fuel and air mixture is disposed in the combustion chamber and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston. The fuel is provided by at least one fuel injector and the air through at least one intake port from an intake manifold. The fuel is provided at high pressure to the fuel injector from a fuel rail in fluid communication with a high-pressure fuel pump that increase the pressure of the fuel received a fuel source. Each of the cylinders has at least two valves, actuated by a camshaft rotating in time with the crankshaft. The valves selectively allow air into the combustion chamber and alternately allow exhaust gases to exit through an exhaust port.

[0033] The air may be distributed to the air intake port(s) through the intake manifold. An air intake duct may provide air from the ambient environment to the intake manifold. In other embodiments, a throttle body may be provided to regulate the flow of air into the manifold. In still other embodiments, a forced air system such as a turbocharger, having a compressor rotationally coupled to a turbine, may be provided. Rotation of the compressor increases the pressure and temperature of the air in the duct and manifold, and an intercooler disposed in the duct may reduce the temperature of the air.

[0034] Exhaust gases 14 produced by the ICE 12 are communicated to an exhaust system 16, which in accordance with the herein described embodiments includes an exhaust gas after-treatment system 18 including one or more exhaust after-treatment devices (not depicted in FIG. 1). The exhaust gases 14 are released from the after-treatment system 18 as treated exhaust gases 20. The after-treatment devices may be any device configured to change the composition of the exhaust gases 14. Some examples of after-treatment devices include, but are not limited to, catalytic converters (two and three way), such as a diesel oxidation catalyst (DOC), lean NOx traps, hydrocarbon adsorbers and selective catalytic reduction (SCR) systems. The after-treatment system 18 may further include a diesel particulate filter (DPF), which may be combined with the SCR to provide an SCRF system. Other embodiments may include an exhaust gas recirculation (EGR) system coupled between the exhaust manifold and the intake manifold. The herein described embodiments are amenable to virtually any combination of after-treatment devices, and it is typical that the after-treatment system 18 will include more than one such device.

[0035] With continued reference to FIG. 1 and reference now also to FIG. 2, in addition to other after-treatment devices that may be provided within the after-treatment system 18 (not depicted in FIG. 2), the after-treatment system 18 includes a SCRF 22. To monitor composition of the treated exhaust gas 20, a NOx sensor 26 is furthermore provided. The NOx sensor 26 provides data in the form of an electric signal output (C.sub.sensor) 28 indicative of a concentration of NOx 32 and ammonia (NH.sub.3) 34 in the treated exhaust gas from the SCRF 22 and emitted as exhaust gas 20.

[0036] A control structure 36 is operatively associated with the after-treatment system 16 and, in accordance with the herein described embodiments, includes an electronic control unit (ECU) 38 and a closed loop observer (CLO) 40. The ECU 38 and the CLO 40 are operatively coupled to receive data in the form of electronic signals from one or more sensors and/or devices associated with the ICE 12 represented as ICE sensor and modules data hereinafter referred to as U.sub.ICE 42. The ECU 28 may receive U.sub.ICE 42 signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 12. The sensors include, but are not limited to, a mass airflow and temperature sensor, a manifold pressure and temperature sensor, a combustion pressure sensor, coolant and oil temperature and level sensors, a fuel rail pressure sensor, a cam position sensor, a crank position sensor, an exhaust pressure sensor and an exhaust temperature sensor, an EGR temperature sensor, and an accelerator pedal position sensor. Furthermore, the ECU 38 may generate output signals to various control devices that are arranged to control the operation of the ICE 12, including, but not limited to, the fuel injectors, the throttle body and other devices forming part of the after-treatment system 18. The ECU 38 may furthermore receive additional control inputs, such as but not limited to, ambient air temperature, ambient pressure, vehicle speed, gear selected, and the like, hereinafter CIs 44.

[0037] In accordance with herein described embodiments, the ECU 38 at least provides a DEF injection signal 46 causing the DEF system (not depicted) to inject a measured quantity of Diesel exhaust fluid or DEF into the exhaust gas flow upstream the SCRF 22. As is known, the DEF is hydrolysized to produce NH.sub.3, which is reacted with the exhaust gas flow within the SCRF 22. An exhaust gas output of the SCRF 22 is exhaust gas consisting primarily of N.sub.2 and H.sub.2O, but also having NOx 32 and NH.sub.3 34 components.

[0038] The NOx sensor 26 is cross-sensitive to both NOx and NH.sub.3, and the data signal C.sub.sensor 28 is a function of the NOx 32 and NH.sub.3 34 components, namely, the actual concentration of NOx or C.sub.NOx and the actual concentration of NH.sub.3 or C.sub.NH3 of the treated exhaust gas 20 output from the SCRF 22.

[0039] Each of the ECU 38 and the CLO 40 may include a digital central processing unit (CPU) having a microprocessor in communication with a memory system, or data carrier, and an interface bus. The microprocessor is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid-state storage, and other non volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the ECU 38 and the CLO 40 to carryout out the steps of such methods and control the ICE 12 and after-treatment system 18. Instead of a CPU, the ECU 38 and/or the CLO 40 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the automotive system 10.

[0040] The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 10 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

[0041] An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

[0042] In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an ASIC, a CD or the like.

[0043] In accordance with the herein described embodiments, the CLO 40 has three operative components, although the CLO 40 may have fewer than the depicted three components, the depicted components may be combined into fewer than three components or expanded to include more than three components. The CLO 40 may furthermore incorporate additional components and functionality associated with the operation of the ICE 12 and/or the after-treatment system 18. In the embodiment depicted in FIG. 2, the CLO 40 includes a selective catalyst reduction (SCR) model 50, a NOx sensor model 52 and a filter 54. The CLO 30 also is operatively coupled to receive the signal 28 from the NOx sensor 26, the DEF injection signal 46 and the U.sub.ICE 42 data. The CLO 30 is operatively configured to provide an estimated ammonia coverage ratio ({circumflex over (θ)}) 58 estimated NH.sub.3 concentration (ĈNH.sub.3) 60 and estimated NOx concentration (Ĉ.sub.NOx) 62 to the ECU 38. The ECU 38 is operatively configured as a closed loop controller employing any suitable control strategy to effect determination and injection of DEF via the DEF injection signal 46 to optimize the estimated concentration of NOx in the emitted exhaust gas 68 given U.sub.ICE 42, CIs 44, {circumflex over (θ)} 58, ĈNH.sub.3 60 and Ĉ.sub.NOx 62.

[0044] The SCR model 50 may be implemented in accordance with the herein described embodiments as a first order lumped model configured to determine the state:

x=Θθ

where x is the ammonia stored within the SCRF 18 in moles [mol], Θ is the maximum ammonia storage capacity and θ is ammonia coverage ratio. Given the following variables: [0045] y.sub.1 is the concentration of NOx at the outlet of the SCR in [g/s] [0046] y.sub.2 is the concentration of NH3 at the outlet of the SCR in [g/s] [0047] F is the exhaust mass flow in [m.sup.3/s] [0048] T is the temperature of the SCR [K]. [0049] u.sub.1 is the concentration of the NOx at the inlet of the SCR in [g/s]. [0050] u.sub.2 is the concentration of NH3 at the inlet of the SCR in [g/s]. [0051] M.sub.NH3 is the molar weight of NH3 [g/mol]. [0052] M.sub.NOx is the molar weight of NOx [g/mol]
and the coefficients:

a.sub.1=e.sup.k.sup.1.sup.-k.sup.5.sup./T

a.sub.2=e.sup.k.sup.2.sup.-k.sup.6.sup./T

a.sub.3=k.sub.3

a.sub.4=e.sup.k.sup.4.sup.-k.sup.7.sup./T

a.sub.5=k.sub.8

x may be given as:

[00001]$\{\begin{array}{c}x\left(k+1\right)=x\left(k\right)+T_{\mathrm{sampling}}\left(\begin{array}{c}\frac{1}{M_{{\mathrm{NH}}_3}}\left(u_2-y_2\right)-\frac{1}{M_{{\mathrm{NO}}_x}}\\ \left(u_1-y_1\right))-a_{1}x\end{array}\right)\\ y_1=\frac{{\mathrm{Fu}}_1}{F+a_{2}x}\end{array}{y}_2=\frac{F\left(u_2+a_{4}x\right)}{F+a_5-a_{3}x}$

where as described above:

y.sub.1=C.sub.NO.sub.x[g/s]

y.sub.2=C.sub.NH.sub.3[g/s]

u.sub.1=C.sub.NO.sub.x,in[g/s]

u.sub.2=C.sub.NH.sub.3,in[g/s]

F=[m.sup.3/s]

T.sub.sampling=[s]

[0053] As noted above, the NOx sensor 26 is cross-sensitive to NH.sub.3, which means it is not possible to have a pure NOx feedback when there is NH.sub.3 present at the outlet of the SCRF 22, which is typical. With reference to FIG. 3, the NOx sensor model 52 takes into account the foregoing parameters: y.sub.1 (70), y.sub.2.sub.2 (72), F (74), and T.sub.sensor (76) and provides the measured signal value y.sub.m (78), where:

y.sub.m=y.sub.1+(ks1+ks2F+ks3T.sub.sensor+ks4F.sup.2)y.sub.2

where (ks1+ks2F+ks3T.sub.sensor+ks4F.sup.2) is defined as cross-sensitivity factor, T.sub.sensor is the temperature at the sensor location and the coefficients ks1-ks4 being determined by bench calibration.

[0054] The filter 54 may be implemented as an extended Kalman filter taking into consideration configuration of the CLO 40 and the NOx sensor 26 characteristics. The filter 54 takes as inputs (e.g., consumes) the NOx sensor 26 output 28 and in particular the NOx 32 and NH.sub.3 34 components of the SCRF 22 output gas, and is used to reconstruct the state (x) i.e., the ammonia coverage ratio stored within the SCRF 22.

[0055] The filter 54 utilizes a plurality of parameters in a typical arrangement. A first covariance matrix (Q) is the covariance matrix of the state (x). A second covariance matrix (R) is the covariance matrix of the NOx sensor 26 measurement. In the described exemplary embodiments, each of the matrices Q and R is 1×1 dimensional.

[0056] In addition to the typical arrangement, the filter also verifies conditions described below. A first condition or NOx sensors comparison is to identify NH3 slip evident condition by comparison of NOx sensors located at inlet and outlet of the catalyst, taking into account an engineering margin. The NOx sensors comparison is used to identify the NH3 slip evident condition taking into account engineering margin.

[0057] A second condition or NH3 condition is that NH3 injection at inlet of the SCR is enabled at least once in a time window in order to avoid the strategy activation when the catalyst is empty. That is, urea injection is enabled at least once in a time window. The second condition is used to avoid to activate the strategy when the catalyst is empty.

[0058] A third condition or NOx sensor 2 condition is to verify NOx sensor 2 is reading above sensor accuracy to avoid strategy activations with very low reading. That is, the third condition is used to avoid strategy activations when the sensor readings are below accuracy or very low reading.

[0059] A fourth condition or linearized model coherency check condition is that the model is misunderstanding NH3 concentration at outlet of the SCR by a model coherency check, when the coherency check is passed the strategy activation is not needed. The linearized model coherency check is used to avoid strategy activations when the linearized model is correct.

[0060] Preferably, if each of the conditions is verified, then the strategy is enabled to obtain an improved NH3 storage estimation. If the strategy is enabled, then the NOx sensor measurement at catalyst outlet can be defined as: [0061] NOxSnsr_real_measure/cross_sensitivity_factor,
and the NOx sensor estimation at catalyst outlet can be defined as: [0062] NOxSnsr_estimation=NH3_only_estimation.

[0063] As will be appreciated from the foregoing discussion, to calibrate the CLO 40 it is necessary to identify the k.sub.j terms of the SCR model 50, the ks.sub.j terms of the NOx sensor model 52 and the Q and R terms of the filter 54. While any suitable methodology may be employed, in an exemplary implementation a one-third/two-thirds bench validation approach is used. For each of a plurality of measurement cycles (e.g., for each of an Artemis cycle, namely a world harmonized light vehicle test cycle (WLTC) and a Federal Test Procedure (FTP) cycle), a dataset is collected from bench testing. In accordance with experimental method and the herein described embodiments, two-thirds of the data is utilized for parameter determination while one-third of the dataset is used for validation for each of the datasets. In this manner, the required terms for the CLO 40 may be established.

[0064] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment is only an example, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.