Method of estimating oxygen storage capacity of catalyst

Abstract

A method of estimating the oxygen storage capacity of a catalyst includes providing an engine system having an internal combustion engine and an exhaust system having a catalyst and an oxygen sensor, providing a three-way catalyst observer model having a Kalman filter and a three-way catalyst kinetic model, estimating a three-way catalyst next time step state and a modeling error, linearizing the three-way catalyst observer model, filtering the estimated three-way catalyst next time step state, and calculating a covariance.

Claims

1. A method of estimating an oxygen storage capacity of a three-way catalyst in an engine system having an internal combustion engine with an exhaust system including a three-way catalyst and an oxygen sensor, an engine control module, and a three-way catalyst observer model including a Kalman filter and a three-way catalyst kinetic model with a three-way catalyst thermal model, the method comprising steps of: sensing a plurality of instant engine control inputs via at least one sensor; estimating of the oxygen storage capacity of the three-way catalyst based on the plurality of the instant engine control inputs via the three-way catalyst observer model; calculating an estimated three-way catalyst oxygen storage capacity next time step state using:
{circumflex over (x)}.sub.k|k-1=f({circumflex over (x)}.sub.k-1|k-1,u.sub.k), and a modeling error using:
{tilde over (y)}.sub.k=z.sub.k−h({circumflex over (x)}.sub.k|k-1), and wherein {circumflex over (x)}.sub.k-1|k-1 is a previous estimated three-way catalyst oxygen storage capacity, uk represents the plurality of the instant engine control inputs, and z.sub.k represents a voltage output of the oxygen sensor; linearizing the three-way catalyst observer model using: $F_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k-1.Math.k-1},u_k},\mathrm{and}$ $H_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k.Math.k-1}}.$ filtering the estimated three-way catalyst oxygen storage capacity next time step state to provide an updated estimated three-way catalyst oxygen storage capacity; and adjusting, using the engine control module, a plurality of engine control parameters based on the updated estimated three-way catalyst oxygen storage capacity.

2. The method of claim 1, wherein the steps of sensing the plurality of the instant engine control inputs include sensing at least one of a pre-catalyst equivalence ratio, a fuel flow rate, exhaust gas pressure, ambient temperature, a pre-catalyst exhaust gas temperature, oxygen sensor voltage, a metered air per cylinder value, an engine speed value, and a fuel control state value via the at least one sensor.

3. The method of claim 1, wherein the steps of filtering the estimated three-way catalyst oxygen storage capacity next time step state to provide an updated estimated three-way catalyst oxygen storage capacity further comprise filtering the estimated three-way catalyst oxygen storage capacity next time step state to provide an updated estimated three-way catalyst oxygen storage capacity using:
P.sub.k|k-1=F.sub.kP.sub.k-1|k-1F.sub.k.sup.T<+Q.sub.k,
S.sub.k=H.sub.kP.sub.k|k-1H.sub.k.sup.TR.sub.k,
K.sub.k=P.sub.k|k-1H.sub.k.sup.TS.sub.k.sup.−1, and
{circumflex over (x)}.sub.k|k={circumflex over (x)}.sub.k|k-1+K.sub.k{tilde over (y)}.sub.k.

4. The method of claim 3, further comprising calculating a result covariance for use in calculating the estimated three-way catalyst oxygen storage capacity next time step state using:
P.sub.k|k=(I−K.sub.kH.sub.k)P.sub.k|k-1.

5. The method of claim 1, the oxygen sensor is a post oxygen switch sensor.

6. The method of claim 1, the oxygen sensor is a pre-catalyst wide-range post oxygen sensor.

7. An engine system for a vehicle, the engine system comprising: an internal combustion engine having an exhaust gas outlet; an exhaust system having a three-way catalyst and an oxygen sensor, and an exhaust gas inlet in downstream communication with the exhaust gas outlet of the internal combustion engine; and an engine control module having a control logic sequence which includes: a first control logic for presenting a plurality of instant engine control inputs being sensed by at least one sensor; a second control logic for estimating a three-way catalyst oxygen storage capacity next time step state using:
{circumflex over (x)}.sub.k|k-1=f({circumflex over (x)}.sub.k-1|k-1,u.sub.k), and a modeling error using:
{tilde over (y)}.sub.k=z.sub.k−h({circumflex over (x)}.sub.k|k-1), wherein {circumflex over (x)}.sub.k-1|k-1 is a previous estimated three-way catalyst oxygen storage capacity, U.sub.k represents the plurality of the instant engine control inputs, and z.sub.x represents a voltage output of the oxygen sensor; a third control logic for linearizing the three-way catalyst observer model using: $F_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k-1.Math.k-1},u_k},\mathrm{and}$ $H_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k.Math.k-1}}.$ wherein the three-way catalyst observer model includes a Kalman filter, a three-way catalyst kinetic model and a three-way catalyst thermal model; a fourth control logic for calculating a filtered estimated three-way catalyst oxygen storage capacity next time step state and calculating a covariance; and a fifth control logic for adjusting, by the engine control module, a plurality of engine control parameters of the internal combustion engine based on the filtered estimated three-way catalyst oxygen storage capacity next time step state.

8. The engine system of claim 7, wherein the oxygen sensor is one of a post oxygen switch sensor and a pre-catalyst wide-range post oxygen sensor.

9. The engine system of claim 8, wherein the plurality of instant engine control inputs of the internal combustion engine include a pre-catalyst equivalence ratio, a fuel flow rate, exhaust gas pressure, ambient temperature, a pre-catalyst exhaust gas temperature, oxygen sensor voltage, a metered air per cylinder value, an engine speed value, and a fuel control state value.

10. The engine system of claim 7, wherein the third control logic or calculating the filtered estimated three-way catalyst oxygen storage capacity next time step state further includes using:
P.sub.k|k-1=F.sub.kP.sub.k-1|k-1F.sub.k.sup.T<+Q.sub.k,
S.sub.k=H.sub.kP.sub.k|k-1H.sub.k.sup.TR.sub.k,
K.sub.k=P.sub.k|k-1H.sub.k.sup.TS.sub.k.sup.−1, and
{circumflex over (x)}.sub.k|k={circumflex over (x)}.sub.k|k-1+K.sub.k{tilde over (y)}.sub.k, and calculating the covariance using:
P.sub.k|k=(I−K.sub.kH.sub.k)P.sub.k|k-1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

(2) FIG. 1 is a schematic cross-section of a catalyst according to the principles of the present disclosure;

(3) FIG. 2 is a schematic of a portion of a catalyst according to the principles of the present disclosure;

(4) FIG. 3 is an operational model of a three-way catalyst according to the principles of the present disclosure;

(5) FIG. 4 is a flowchart depicting steps of a method according to the principles of the present disclosure, and

(6) FIG. 5 is a graph showing an estimation of oxygen storage capacity of a catalyst over time according to the principles of the present disclosure.

DESCRIPTION

(7) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. The term “about” as used in the description is defined as an amount around a specific number that does not have a significant impact on the results of the operation.

(8) Referring to FIGS. 1 and 2, a schematic for an engine system 10 for a vehicle is illustrated and will now be described. The engine system 10 includes an internal combustion engine (ICE) 12, an exhaust system 14, and an engine control module 15. The exhaust system 14 includes a catalyst assembly 16 and an oxygen sensor 18. More particularly, the catalyst assembly 16 has an exhaust gas inlet 20 and an exhaust gas outlet 22, and a three-way catalyst 24. The oxygen sensor 18 is disposed in the exhaust gas outlet 22 and may be a post oxygen switch sensor or a pre-catalyst wide-range post oxygen sensor. The exhaust gas inlet 20 receives exhaust gas from the ICE and directs the exhaust gas to the three-way catalyst 24. The three-way catalyst 24 includes a ceramic substrate 26 on which is disposed a catalytic metal coating 28. In the present example, the catalytic metal coating 28 includes Cerium Oxide (Ce.sub.2O.sub.3). However, other metal oxides or combinations of metal oxides may be incorporated into the three-way catalyst 24 without departing from the scope of the present disclosure. For example, the catalytic metal coating 28 may include oxides of Rhodium (Rh), Palladium (Pd), and Platinum (Pt) among other metal oxides.

(9) The engine control module 15 is preferably an electronic control device having a preprogrammed digital computer or processor, control logic, memory used to store data, and at least one I/O peripheral. The control logic includes a plurality of logic routines for monitoring, manipulating, and generating data. The engine control module 15 controls the plurality of actuators, pumps, valves, and other devices associated with the engine system 10 control according to the principles of the present disclosure. The control logic may be implemented in hardware, software, or a combination of hardware and software. For example, control logic may be in the form of program code that is stored on the electronic memory storage and executable by the processor. The engine control module 15 receives the output signal of each of several sensors on the vehicle, performs the control logic and sends command signals to several control devices. For example, a control logic implemented in software program code that is executable by the processor of the engine control module 15 includes a control logic for implementing a method described further below.

(10) For the purposes of the present disclosure, the three-way catalyst is virtually separated into a plurality of segments 30. One such segment 31, is shown in FIG. 2 and represents a one dimensional portion through which the catalytic reactions occur. The constituents of the exhaust gas going into the segment includes [O.sub.2].sub.in, [CO].sub.in, [CO.sub.2].sub.in, [H.sub.2].sub.in, and [H.sub.2O].sub.in at an incoming gas temperature T.sub.gin. After the catalytic reaction, the treated gas coming out of the segment includes [O.sub.2].sub.out, [CO].sub.out, [CO.sub.2].sub.out, [H.sub.2].sub.out, and [H.sub.2O].sub.out at an outgoing gas temperature T.sub.gout. For example, a first catalytic reaction is an Oxygen storage reaction represented by the following:

(11) $O_2+2{\mathrm{Ce}}_2{O}_3.Math.2{\mathrm{Ce}}_2{O}_4;$$r_1=k_1^f{{\mathrm{OSC}}^2\left(1-{\phi }_{O_2}\right)}^2\left[O_2\right]-k_1^b{\mathrm{OSC}}^2{\phi }_{O_2}^2{C}_0;$$k_1^f=A_1^f{e}^{-\frac{E_1^f}{T}},\mathrm{and}$$k_1^b=A_1^b{e}^{-\frac{E_1^b}{T}}.$

(12) A second catalytic reaction is a Carbon Monoxide Oxidation reaction represented by the following:

(13) $\mathrm{CO}+{\mathrm{Ce}}_2{O}_4.Math.{\mathrm{CO}}_2+{\mathrm{Ce}}_2{O}_3;$$r_2=k_2^f\mathrm{OSC}{\phi }_{O_2}\left[\mathrm{CO}\right]-k_2^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)\left[{\mathrm{CO}}_2\right];$$k_2^f=A_2^f{e}^{-\frac{E_2^f}{T}},\mathrm{and}$$k_2^b=A_2^b{e}^{-\frac{E_2^b}{T}}.$

(14) A third catalytic reaction is a Hydrogen Oxidation reaction represented by the following:

(15) $H_2+{\mathrm{Ce}}_2{O}_4.Math.H_{2}O+{\mathrm{Ce}}_2{O}_3;$$r_3=k_3^f\mathrm{OSC}{\phi }_{O_2}\left[H_2\right]-k_3^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)\left[H_{2}O\right];$$k_3^f=A_3^f{e}^{-\frac{E_3^f}{T}},\mathrm{and}$$k_3^b=A_3^b{e}^{-\frac{E_3^b}{T}}.$

(16) Oxygen storage value (OSV) is calculated using the following equation, where OSC is the oxygen storage capacity:

(17) $\mathrm{OSC}\frac{\partial {\phi }_{O_2}}{\partial t}=2r_1-r_2-r_3.$

(18) The treated exhaust gas constituents coming out of the catalyst segment are calculated as follows:

(19) ${\left[O_2\right]}_{\mathrm{out}}={\frac{{\left[O_2\right]}_{\mathrm{in}}+k_1^b{\mathrm{OSC}}^2{\phi }_{O_2}^2{C}_0{t}_r}{1+k_1^f{{\mathrm{OSC}}^2\left(1-{\phi }_{O_2}\right)}^2{t}_r}\left[\mathrm{CO}\right]}_{\mathrm{out}}={\frac{{\left[\mathrm{CO}\right]}_{\mathrm{in}}+\left({\left[\mathrm{CO}\right]}_{\mathrm{in}}+{\left[{\mathrm{CO}}_2\right]}_{\mathrm{in}}\right)k_2^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r}{1+k_2^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r+k_2^f\mathrm{OSC}{\phi }_{O_2}{t}_r}\left[{\mathrm{CO}}_2\right]}_{\mathrm{out}}={\frac{{\left[{\mathrm{CO}}_2\right]}_{\mathrm{in}}+\left({\left[\mathrm{CO}\right]}_{\mathrm{in}}+{\left[{\mathrm{CO}}_2\right]}_{\mathrm{in}}\right)k_2^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r}{1+k_2^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r+k_2^f\mathrm{OSC}{\phi }_{O_2}{t}_r}\left[H_2\right]}_{\mathrm{out}}={\frac{{\left[H_2\right]}_{\mathrm{in}}+\left({\left[H_2\right]}_{\mathrm{in}}+{\left[H_{2}O\right]}_{\mathrm{in}}\right)k_3^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r}{1+k_3^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r+k_3^f\mathrm{OSC}{\phi }_{O_2}{t}_r}\left[H_{2}O\right]}_{\mathrm{out}}=\frac{{\left[H_{2}O\right]}_{\mathrm{in}}+\left({\left[\mathrm{CO}\right]}_{\mathrm{in}}+{\left[{\mathrm{CO}}_2\right]}_{\mathrm{in}}\right)k_3^f\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r}{1+k_3^b\mathrm{OSC}\left(1-{\phi }_{O_2}\right)t_r+k_3^f\mathrm{OSC}{\phi }_{O_2}{t}_r}$

(20) Turning now to FIG. 3, a three-way catalyst observer model 32 is illustrated and will now be described. The three-way catalyst observer model 32 includes a Kalman filter 34 and a three-way catalyst kinetic model 36. The three-way catalyst kinetic model 36 includes a three-way catalyst thermal model 38. Inputs 40 into the three-way catalyst observer model 32 include a pre-catalyst equivalence ratio, a fuel flow rate, exhaust gas pressure, ambient temperature, a pre-catalyst exhaust gas temperature, oxygen sensor 18 voltage, a metered air per cylinder value, an engine speed value, and a fuel control state value. Outputs 42 of the three-way catalyst observer model 32 include an oxygen storage value (OSV), a post-catalyst equivalence ratio (EQR), a post-catalyst switch voltage, OSC, and a pre-catalyst EQR offset.

(21) Turning now to FIG. 4 with continuing reference to FIG. 3, a flowchart is illustrated for a method 50 of dynamically estimating the OSC of the three-way catalyst 24. The method 50 includes a first step (or first control logic) 51 of sensing a plurality of instant engine control inputs via at least one sensor. A second step (or second control logic) 52 estimates the oxygen storage capacity of the three-way catalyst based on the plurality of the instant engine control inputs via the three-way catalyst observer model. A third step (or third control logic) 53 includes calculating an estimated a three-way catalyst next time step state and a modeling error using:
{circumflex over (x)}.sub.k|k-1=f({circumflex over (x)}.sub.k-1|k-1,u.sub.k)(predicted state estimate), and
{tilde over (y)}.sub.k=z.sub.k−h({circumflex over (x)}.sub.k|k-1)(innovation).
In the first equation or predicted state estimate, {circumflex over (x)} is the estimate of OSC and u.sub.k is the input or measured engine-out air to fuel ratio. At time k, the observation or measurement z.sub.k is the oxygen sensor voltage measurement. A fourth step (or fourth control logic) 54 linearizes the three-way catalyst observer model using:

(22) $F_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k-1.Math.k-1},u_k},\mathrm{and}$$H_k=\frac{\partial y}{\partial x}{.Math.}_{{\hat{x}}_{k.Math.k-1}}.$
A fifth step (or fifth control logic) 56 filters the estimated three-way catalyst next time step state and calculates a covariance using:
P.sub.k|k-1=F.sub.kP.sub.k-1|k-1F.sub.k.sup.T<+Q.sub.k (predicted error covariance),
S.sub.k=H.sub.kP.sub.k|k-1H.sub.k.sup.TR.sub.k (innovation covariance),
K.sub.k=P.sub.k|k-1H.sub.k.sup.TS.sub.k.sup.−1 (optimal Kalman gain),
{circumflex over (x)}.sub.k|k={circumflex over (x)}.sub.k|k-1+K.sub.k{tilde over (y)}.sub.k (updated estimate), and
P.sub.k|k=(I−K.sub.kH.sub.k)P.sub.k|k-1 (updated estimate covariance).
A sixth step (or sixth control logic) 58 adjusts, using the engine control module, a plurality of engine control input parameters based on the updated estimated three-way catalyst oxygen storage capacity.

(23) Incorporating the above disclosed method 50 into control logic that is operational by the engine control module 15 includes a first control logic for estimating a three-way catalyst next time step state and a modeling error using a plurality of measured inputs including a pre-catalyst equivalence ratio, a fuel flow rate, exhaust gas pressure, ambient temperature, a pre-catalyst exhaust gas temperature, oxygen sensor 18 voltage, a metered air per cylinder value, an engine speed value, and a fuel control state value. A second control logic linearizes the three-way catalyst observer model. A third control logic filters the estimated three-way catalyst next time step state and calculates a covariance.

(24) With reference to FIG. 5, a graph 60 depicting the performance of the three-way catalyst observer model 32 and method 50 is illustrated and will now be described. The graph 60 includes a y-axis 62 depicting the estimated OSC over time 64 in seconds (x-axis). The dashed reference lines represent Worst Performing Acceptable (WPA) mean 66, WPA −4σ 68, Best Performing Unacceptable (BPU) +2σ 70 (70 is for BPU with a WPA post O2 sensor), and BPU mean 72. The performance lines represent calculated time-based WPA mean 74, time-based WPA −4σ 76, time-based BPU +2σ 78, and time-based BPU mean 80. The vertical dashed line represents the equivalent time of two Federal Test Procedure (FTP) cycles 82. The several lines contained by the bracket 83 represent the WPA degraded post oxygen sensor. The several lines contained by the bracket 84 represent the non-degraded post oxygen sensor. The bracket 86 represents the difference between the WPA −4σ and BPU +2σ.

(25) Estimated OSC is used to determine fuel strategy. For example, when estimated OSC is low, a lean fuel strategy (air/fuel ratio is less than stoichiometric) is incorporated to introduce less fuel into the engine. Less fuel requires less Oxygen to burn the fuel leaving more Oxygen to store in the catalyst. Alternatively, stoichiometric and rich air/fuel ratio leaves less Oxygen available to store in the catalyst and therefore the oxidation of CO and H2 in the catalyst depletes the Oxygen storage of the catalyst. Current fuel strategies do not have the input of an accurate OSC estimation and therefore are required to assume OSC is low and requires more Oxygen to increase storage leading to reduced engine performance and higher fuel consumption. The capability to have a more accurate OSC estimation allows engine calibration to more accurately determine when the catalyst requires Oxygen to increase OSC and therefore run a fuel strategy more tailored to engine performance and other parameters that fuel strategy is used to control.

(26) The oxygen storage capacity of the catalyst 24 is an indicator of the ability of the catalyst to effectively reduce emissions. For example, if the catalyst has aged to a significant extent, the oxygen storage capacity will be low and the catalyst can be deemed to be insufficient to perform its emission reduction function when then oxygen storage capacity is below a threshold. In addition, if the wrong type of catalyst is installed in a vehicle, it may also not meet the threshold oxygen storage capacity, which would also indicate that the catalyst is not function property. Therefore, the present system is configured to send a signal indicating that the oxygen storage capacity is below the threshold, so that corrective action may be taken. For example, the signal may be used actuate a malfunction light, such as a “check engine” light. In addition, or in the alternative, the signal may be used by the vehicle controller to perform other corrective actions, such as limiting the vehicle's fuel supply until the catalyst is replaced and meets the oxygen storage capacity minimum threshold.

(27) While examples have been described in detail, those familiar with the art to which this disclosure relates will recognize various alternative designs and examples for practicing the disclosed method within the scope of the appended claims.