Exhaust component calculation system

Abstract

To provide an exhaust gas constituent calculation system capable of suppressing deterioration of calculation accuracy of at least one of NOx concentration and NH3 concentration in exhaust gas.SOLUTION: A NOx sensor provided downstream of the three way catalytic converter; and a calculation device configured to calculate at least one of a concentration of NOx in exhaust gas from the three way catalytic converter and a concentration of NH3, the calculation device includes a first calculation unit configured to calculate a second correlation value correlating with the oxygen concentration of the three-way catalytic converter exhaust gas based on the pump cell current of the NOx sensor, a second calculation unit configured to refer to a ratio map defining a ratio of at least one of the NOx concentration and the NH3 concentration of the three-way catalytic converter exhaust gas according to the first correlation value and the second correlation value, and output the ratio, and a third calculation unit configured to output at least one of the NOx concentration and the NH3 concentration of the three-way catalytic converter exhaust gas based on the ratio and the NOx sensor output value. When the second correlation value is abnormal with respect to the detected first correlation value, the ratio map defines a ratio when the second correlation value is normal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas component calculation system. [Background technology]

[0002] The oxygen concentration in the exhaust gas and the air-fuel ratio of the exhaust gas can be calculated based on the pump cell current of the NOx sensor exposed to the exhaust gas from the engine. Furthermore, based on the oxygen concentration or air-fuel ratio calculated in this way, the NOx concentration can be calculated with high accuracy by excluding the proportion of the NH3 concentration in the exhaust gas that accounts for the output value of the NOx sensor (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-215334 Summary of the Invention [Problem to be solved by the invention]

[0004] Due to deterioration of the NOx sensor over time or exposure to heat, the oxygen concentration and air-fuel ratio calculated based on the pump cell current may be abnormal values. If the NOx concentration and NH3 concentration in the exhaust gas are calculated based on such abnormal oxygen concentration and air-fuel ratio values, the calculation accuracy may be reduced.

[0005] Therefore, an object of the present invention is to provide an exhaust gas component calculation system that suppresses a decrease in the accuracy of calculating at least one of the NOx concentration and the NH3 concentration in the exhaust gas. [Means for solving the problem]

[0006] The object is to provide an engine having an exhaust passage, the engine including a three-way catalyst having an oxygen storage capacity, a gas sensor arranged in the exhaust passage upstream of the three-way catalyst and detecting a first correlation value correlating with the oxygen concentration in the exhaust gas flowing into the three-way catalyst, a NOx sensor arranged in the exhaust passage downstream of the three-way catalyst, and a calculation device for calculating at least one of the NOx concentration and the NH3 concentration in the exhaust gas discharged from the three-way catalyst, the calculation device including a first calculation unit that calculates a second correlation value correlating with the oxygen concentration in the exhaust gas discharged from the three-way catalyst based on a pump cell current of the NOx sensor, and a calculation unit that calculates at least one of the NOx concentration and the NH3 concentration in the exhaust gas discharged from the three-way catalyst based on a pump cell current of the NOx sensor. and a third calculation unit that calculates at least one of the NOx concentration and the NH3 concentration in the exhaust gas discharged from the three-way catalyst based on the ratio and the output value of the NOx sensor, wherein the ratio map specifies the ratio for when the second correlation value is a normal value for the detected first correlation value when the second correlation value calculated for the detected first correlation value is an abnormal value. [Effects of the Invention]

[0007] It is possible to provide an exhaust component calculation system that suppresses a decrease in the accuracy of calculating at least one of the NOx concentration and the NH3 concentration in the exhaust. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an exhaust component calculation system. [Figure 2] FIG. 2A is a flowchart illustrating an example of exhaust component calculation control, and FIG. 2B is a diagram illustrating an NH3 ratio map. [Figure 3] FIG. 3 is a timing chart illustrating the exhaust component calculation control. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Outline of exhaust component calculation system] FIG. 1 is a schematic diagram of an exhaust component calculation system 1. The exhaust component calculation system 1 is mounted on, for example, a vehicle, but is not limited thereto and may also be mounted on a vessel or other device other than a vehicle. The exhaust component calculation system 1 has an engine 10 and an exhaust passage 20. The engine 10 is a multi-cylinder engine having multiple cylinders. The engine 10 is provided with an ignition plug and an in-cylinder injection valve. An intake passage (not shown) is also connected to the engine 10.

[0010] The exhaust passage 20 includes an exhaust manifold 21 connected to the engine 10, and an exhaust pipe 22 downstream of the exhaust manifold 21. An upstream catalyst 31 is arranged between the exhaust manifold 21 and the exhaust pipe 22. A downstream catalyst 32 is arranged in the exhaust pipe 22. An upstream air-fuel ratio sensor 41 is provided at the junction of branch sections connected to each cylinder of the exhaust manifold 21. A downstream air-fuel ratio sensor 42 is provided in the exhaust pipe 22 downstream of the upstream catalyst 31. A NOx sensor 43 is provided in the exhaust pipe 22 downstream of the downstream catalyst 32. The upstream air-fuel ratio sensor 41 detects the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 31. The downstream air-fuel ratio sensor 42 detects the air-fuel ratio of the exhaust gas discharged from the upstream catalyst 31 and flowing into the downstream catalyst 32. The downstream air-fuel ratio sensor 42 is an example of a gas sensor. The NOx sensor 43 calculates the NOx concentration and NH3 concentration in the exhaust gas discharged from the downstream catalyst 32 based on the output value of the NOx sensor 43, which will be described in detail later.

[0011] The upstream catalyst 31 and downstream catalyst 32 are three-way catalysts containing catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and possessing oxygen storage capacity. The three-way catalyst, with its catalytic activity and oxygen storage capacity, purifies NOx and HC according to the amount of oxygen stored. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, the three-way catalyst stores oxygen in the exhaust gas if the amount of oxygen stored in the three-way catalyst is small. This reduces and purifies NOx in the exhaust gas. When the amount of oxygen stored in the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust gas flowing out of the three-way catalyst increase. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich, the three-way catalyst releases the oxygen stored in the three-way catalyst if the amount of oxygen stored in the three-way catalyst is large, and HC in the exhaust gas is oxidized and purified. When the amount of oxygen stored in the three-way catalyst decreases, the concentration of HC in the exhaust gas flowing out of the three-way catalyst increases. In addition, NH3 is produced from NOx in a three-way catalyst.

[0012] The ECU (Electric Control Unit) 50 includes a central processing unit (CPU), random access memory (RAM), read only memory (ROM), and storage devices such as flash memory, and performs various controls by executing programs stored in the ROM and storage devices. The ECU 50 controls the engine 10 based on the amount of operation of the accelerator pedal and brake pedal operated by the driver, the engine speed and load of the engine 10, etc. The ECU 50 receives as input the detected air-fuel ratios detected by the upstream air-fuel ratio sensor 41 and the downstream air-fuel ratio sensor 42, respectively, and the output value of the NOx sensor 43. The ECU 50 is an example of a calculation device that calculates the NH3 concentration and NOx concentration in exhaust gas, which will be described in detail later. The ECU 50 functionally realizes a first calculation unit, a second calculation unit, and a third calculation unit, which will be described in detail later.

[0013] The ECU 50 controls the target air-fuel ratio, which is a target value of the air-fuel ratio of the exhaust gas discharged from the engine 10, so that it alternates between a rich air-fuel ratio or a stoichiometric air-fuel ratio that is lower than the stoichiometric air-fuel ratio (for example, 14.6) and a lean air-fuel ratio that is higher than the stoichiometric air-fuel ratio. Specifically, the ECU 50 controls the air-fuel ratio of the exhaust gas discharged from the engine 10 so that the air-fuel ratio detected by the upstream air-fuel ratio sensor 41 becomes the target air-fuel ratio. Specifically, the ECU 50 controls the air-fuel ratio of the exhaust gas discharged from the engine 10 by feedback-controlling the air-fuel ratio detected by the upstream air-fuel ratio sensor 41, the air-fuel ratio detected by the downstream air-fuel ratio sensor 42, and mainly the fuel injection amount.

[0014] [Exhaust component calculation control] The exhaust component calculation control executed by the ECU 50 will now be described. Fig. 2A is a flowchart illustrating the exhaust component calculation control. The ECU 50 acquires the output value of the NOx sensor 43 (step S1). The ECU 50 detects the air-fuel ratio detected by the downstream air-fuel ratio sensor 42, i.e., the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 32 (step S2). The detected air-fuel ratio of the downstream air-fuel ratio sensor 42 is an example of a first correlation value.

[0015] The ECU 50 calculates the oxygen concentration in the exhaust gas discharged from the downstream catalyst 32 based on the pump cell current of the NOx sensor 43 (step S3). The calculation of the oxygen concentration based on the pump cell current may be performed using a known method, for example, as described in Japanese Patent Application Laid-Open No. 2015-215334. The calculated oxygen concentration is an example of a second correlation value. Step S3 is an example of processing executed by a first calculation unit.

[0016] The ECU 50 refers to the NH3 ratio map that defines the ratio of NH3 according to the detected air-fuel ratio and the oxygen concentration, and calculates the NH3 ratio that the NH3 concentration accounts for in the output value of the NOx sensor 43 (step S4). Step S4 is an example of processing executed by the second calculation unit.

[0017] FIG. 2B is an example diagram of an NH3 ratio map. The higher the NH3 ratio, the lower the NOx ratio, which is the ratio of the NOx concentration to the output value of the NOx sensor 43. In the map of FIG. 2B, the NH3 ratio ranges from 1 to 0. An NH3 ratio of "1" indicates that the NH3 concentration accounts for the entire output value of the NOx sensor 43. An NH3 ratio of "0" indicates that the NOx concentration accounts for the entire output value of the NOx sensor 43. The NH3 ratio map of FIG. 2B specifies that the NH3 ratio increases as the detected air-fuel ratio becomes richer than the stoichiometric air-fuel ratio and the oxygen concentration decreases, and decreases as the detected air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio and the oxygen concentration increases. In this embodiment, when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is calculated as "0." When the air-fuel ratio of the exhaust gas is rich, the oxygen concentration in the exhaust gas is calculated as a value lower than "0." When the air-fuel ratio of the exhaust gas is lean, the oxygen concentration in the exhaust gas is calculated as a value higher than "0."

[0018] Based on the ratio calculated in step S4, the ECU 50 calculates the NH3 concentration and the NOx concentration in the exhaust gas discharged from the downstream catalyst 32 (step S5). Specifically, the following calculation formulas are used. NH3 concentration = NOx sensor 43 output value x NH3 ratio NOx concentration = output value of NOx sensor 43 × (1-NH3 ratio) Step S5 is an example of a process executed by the third calculation unit.

[0019] Fig. 3 is a timing chart illustrating the exhaust component calculation control. Fig. 3 shows the output value of the NOx sensor 43, the detected air-fuel ratio of the downstream air-fuel ratio sensor 42, and the transitions of the calculated oxygen concentration, NOx concentration, and NH3 concentration. The NH3 ratio map in Fig. 2B shows the NH3 ratio used corresponding to the time of the timing chart.

[0020] When the output value of the NOx sensor 43 increases, if the detected air-fuel ratio is lean and the oxygen concentration is high (time t1), the NH3 ratio is calculated to be "0" based on the NH3 ratio map, and the NOx concentration is calculated assuming that the NOx concentration accounts for the entire output value of the NOx sensor 43. When the output value of the NOx sensor 43 increases, if the detected air-fuel ratio is rich and the oxygen concentration is low (time t2), the NH3 ratio is calculated to be "1" based on the NH3 ratio map, and the NH3 concentration is calculated assuming that the NH3 concentration accounts for the entire output value of the NOx sensor 43.

[0021] When the output value of the NOx sensor 43 increases, if the detected air-fuel ratio is a rich air-fuel ratio and the oxygen concentration is 0 (time t3), the NH3 ratio is calculated as "1" based on the NH3 ratio map, and the NH3 concentration is calculated assuming that the NH3 concentration accounts for the entire output value of the NOx sensor 43.

[0022] Here, when the detected air-fuel ratio of the downstream air-fuel ratio sensor 42 is a rich air-fuel ratio and the oxygen concentration in the exhaust gas discharged from the downstream catalyst 32 is “0,” this indicates that the downstream catalyst 32 releases stored oxygen to the rich air-fuel ratio exhaust gas flowing into the downstream catalyst 32, resulting in the discharge of exhaust gas at the stoichiometric air-fuel ratio. However, this is practically difficult to achieve, considering the rate at which the stored oxygen is released from the downstream catalyst 32. Therefore, in such a case, the actual oxygen concentration should be lower than “0,” and it is suspected that the oxygen concentration was calculated as an abnormal value due to aging or heating of the NOx sensor 43. For this reason, the NH3 ratio map specifies the NH3 ratio as “1” when the calculated oxygen concentration for the detected air-fuel ratio is abnormal, just as it does when the oxygen concentration is normal for the detected air-fuel ratio (at time t2). As a result, even when the calculated oxygen concentration is abnormal, the NH3 concentration can be accurately calculated according to the NH3 ratio map without being directly affected by the calculated oxygen concentration.

[0023] Instead of the NH3 ratio map shown in FIG. 2B, a NOx ratio map that defines the NOx ratio of the NOx concentration relative to the output value of the NOx sensor 43 may be used. Although both the NOx concentration and the NH3 concentration are calculated in this embodiment, only one of them may be calculated. Instead of the downstream air-fuel ratio sensor 42, an oxygen concentration sensor that detects the oxygen concentration in the exhaust may be used. In this case, the oxygen concentration is an example of a first correlation value that correlates with the oxygen concentration in the exhaust flowing into the downstream catalyst 32. Instead of calculating the oxygen concentration based on the pump cell current of the NOx sensor 43, the air-fuel ratio of the exhaust may be calculated based on the pump cell current. In this case, the air-fuel ratio is an example of a second correlation value that correlates with the oxygen concentration in the exhaust discharged from the downstream catalyst 32.

[0024] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims. [Explanation of symbols]

[0025] 1. Exhaust component calculation system 32 Downstream catalyst (three-way catalyst) 42 Downstream air-fuel ratio sensor (gas sensor) 43 NOx sensor 50 ECU (calculation device, first calculation unit, second calculation unit, third calculation unit)

Claims

[Claim 1] a three-way catalyst disposed in an exhaust passage of the engine and having an oxygen storage capacity; a gas sensor that is disposed in the exhaust passage upstream of the three-way catalyst and detects a first correlation value that correlates with the oxygen concentration in the exhaust gas flowing into the three-way catalyst; a NOx sensor disposed in the exhaust passage downstream of the three-way catalyst; The NOx concentration and NH ３ a calculation device for calculating at least one of the concentrations, The calculation device a first calculation unit that calculates a second correlation value that correlates with the oxygen concentration in the exhaust gas discharged from the three-way catalyst based on a pump cell current of the NOx sensor; The NOx concentration and the NH concentration in the exhaust gas discharged from the three-way catalyst are calculated according to the first correlation value and the second correlation value. ３ a second calculation unit that calculates the ratio by referring to a ratio map that defines a ratio of at least one of the concentrations; Based on the ratio and the output value of the NOx sensor, the NOx concentration and NH ３ a third calculation unit that calculates at least one of the concentrations, the ratio map defines the ratio when the second correlation value calculated for the detected first correlation value is an abnormal value, and when the second correlation value is a normal value for the detected first correlation value. Exhaust gas component calculation system.

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