Ammonia concentration calculation device

Abstract

To provide an ammonia concentration calculation device capable of accurately calculating a concentration of ammonia in exhaust gas.SOLUTION: An ammonia concentration calculation device includes: an acquisition section that acquires a temperature of a catalyst disposed in an exhaust passage of an internal combustion engine, an oxygen storage possible amount of the catalyst and an output value of a NOx sensor disposed downstream of the catalyst in the exhaust passage; and a calculation section that calculates a concentration of ammonia in exhaust gas flowing downstream of the catalyst on the basis of the temperature, the oxygen storage possible amount and the output value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an ammonia concentration calculation device. [Background technology]

[0002] Patent Document 1 describes the relationship between the temperature of a catalyst and the amount of ammonia produced in the catalyst. Patent Document 2 describes detecting the concentration of ammonia in exhaust gas based on the output value of a NOx sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-034202 A [Patent Document 2] JP 2023-003623 A Summary of the Invention [Problem to be solved by the invention]

[0004] It is conceivable to calculate the concentration of ammonia in the exhaust gas based on the temperature of the catalyst and the output value of the NOx sensor. However, the amount of ammonia produced in the catalyst varies depending on the performance of the catalyst. Therefore, there is a risk that the accuracy of calculating the concentration of ammonia will decrease if only the temperature of the catalyst and the output value of the NOx sensor are used as described above.

[0005] Therefore, an object of the present invention is to provide an ammonia concentration calculation device that can accurately calculate the concentration of ammonia in exhaust gas. [Means for solving the problem]

[0006] The above object can be achieved by an ammonia concentration calculation device including: an acquisition unit that acquires a temperature of a catalyst arranged in an exhaust passage of an internal combustion engine, an oxygen storable amount of the catalyst, and an output value of a NOx sensor arranged downstream of the catalyst in the exhaust passage; and a calculation unit that calculates the concentration of ammonia in exhaust gas flowing downstream of the catalyst based on the temperature, the oxygen storable amount, and the output value. Effect of the Invention

[0007] It is possible to provide an ammonia concentration calculation device that can accurately calculate the concentration of ammonia in exhaust gas. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of the engine. [Diagram 2] FIG. 2 is a flowchart illustrating an example of the ammonia concentration calculation control. [Diagram 3] FIG. 3A is an example of a map that defines the ammonia ratio according to the temperature and the oxygen storable amount of the front catalyst, and FIG. 3B is an example of a map that defines the ammonia ratio according to the temperature and the oxygen storable amount of the rear catalyst. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Engine 1 schematic configuration] FIG. 1 is a schematic diagram of an engine 1. The engine 1 is mounted on, for example, a vehicle, but is not limited thereto, and may be mounted on a vessel or the like other than a vehicle. The engine 1 is an example of an internal combustion engine, and may be, for example, a gasoline engine, but may also be a diesel engine. The engine 1 has an engine body 10, an intake passage 20, and an exhaust passage 30. The engine body 10 is a multi-cylinder engine having a plurality of cylinders, and a combustion chamber 11, a piston 12, an ignition plug 16, and the like are provided in each cylinder. In addition, a connecting rod 13 and a crankshaft 14 are arranged inside the engine body 10. The piston 12 is connected to the crankshaft 14 by the connecting rod 13. The engine body 10 is provided with a rotation speed sensor 15, and an in-cylinder injection valve 17 is provided for each cylinder. The rotation speed sensor 15 detects the rotation speed of the crankshaft 14 to detect the rotation speed of the engine body 10. The in-cylinder injection valve 17 directly injects fuel into the combustion chamber 11. Incidentally, a port injection valve that injects fuel toward an intake port of the engine body 10 may be provided instead of the in-cylinder injection valve 17, or a port injection valve may be provided in addition to the in-cylinder injection valve 17. The spark plug 16 ignites the air-fuel mixture in the combustion chamber 11. An intake passage 20 and an exhaust passage 30 are connected to the intake port and exhaust port of the engine body 10, respectively. An intake valve 18a and an exhaust valve 18b open and close the intake port and exhaust port of the engine body 10, respectively.

[0010] In the intake passage 20, an air cleaner 21, an air flow meter 22, and a throttle valve 23 are provided in this order from upstream to downstream. The air cleaner 21 removes dust and other particles from the air flowing in from the outside. The air flow meter 22 acquires the amount of intake air. The throttle valve 23 is driven by, for example, an actuator (not shown) to adjust the amount of intake air.

[0011] When intake valve 18a opens, air is introduced from intake passage 20 into combustion chamber 11. A mixture of air and fuel injected from in-cylinder injection valve 17 is compressed by piston 12 and ignited by spark plug 16. Ignition of the mixture causes piston 12 to reciprocate up and down within combustion chamber 11, rotating crankshaft 14. Exhaust gas after combustion is discharged from exhaust passage 30.

[0012] In the exhaust passage 30, from upstream to downstream, there are provided a front-stage catalyst 32a, a front-stage temperature sensor 33a, a rear-stage catalyst 32b, a rear-stage temperature sensor 33b, and a NOx sensor 34. The front-stage temperature sensor 33a detects the temperature of the exhaust gas discharged from the front-stage catalyst 32a and flowing into the rear-stage catalyst 32b. The rear-stage temperature sensor 33b detects the temperature of the exhaust gas discharged from the rear-stage catalyst 32b. The NOx sensor 34 detects the concentration of NOx in the exhaust gas discharged from the rear-stage catalyst 32b.

[0013] The front catalyst 32a and the rear catalyst 32b are three-way catalysts containing catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and having oxygen storage capacity. The three-way catalyst has a catalytic action and an oxygen storage capacity, and therefore has a purification action of NOx and HC according to the amount of oxygen stored. That is, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, the oxygen in the exhaust gas is stored by the three-way catalyst when the amount of oxygen stored in the three-way catalyst is small. Accordingly, the NOx in the exhaust gas is reduced and purified. When the amount of oxygen stored in the three-way catalyst increases, the concentration of oxygen and NOx in the exhaust gas flowing out from the three-way catalyst increases. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich, when the amount of oxygen stored in the three-way catalyst is large, the oxygen stored in the three-way catalyst is released, and the HC in the exhaust gas is oxidized and purified.

[0014] When exhaust gas containing HC, CO, and water flows into such a three-way catalyst, hydrogen is produced by catalytic action. Ammonia is produced when NOx in the exhaust reacts with hydrogen. The amount of ammonia produced depends on the performance of the three-way catalyst. The higher the performance of the three-way catalyst, the more the reaction between NOx in the exhaust and hydrogen is promoted, and the greater the amount of ammonia produced. The performance of the three-way catalyst correlates with the amount of oxygen that can be stored. If a three-way catalyst is used for a long period of time, the performance of the three-way catalyst will deteriorate, and the amount of oxygen that can be stored will also decrease.

[0015] The ECU (Electric Control Unit) 100 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage device such as a flash memory, and performs various controls by executing programs stored in the ROM or the storage device. The ECU 100 controls the spark plug 16, the in-cylinder injection valve 17, and the throttle valve 23 based on the amount of operation of the accelerator pedal or the brake pedal operated by the driver, the rotation speed and the load of the engine body 10, and the like. The ECU 100 receives the rotation speed detected by the rotation speed sensor 15, the intake air amount detected by the air flow meter 22, and the output values ​​of the front stage temperature sensor 33a, the rear stage temperature sensor 33b, and the NOx sensor 34. The ECU 100 is an example of an ammonia concentration calculation device. In addition, the ECU 100 functionally realizes an acquisition unit and a calculation unit, which will be described later, by the above-mentioned CPU, RAM, ROM, and storage device.

[0016] [Ammonia concentration calculation control] 2 is a flowchart illustrating the ammonia concentration calculation control. This control is repeatedly executed while the ignition is on. The ECU 100 determines whether or not the engine 1 has been started (step S1). If the result in step S1 is No, this control ends.

[0017] If the answer is Yes in step S1, the ECU 100 acquires the temperatures of the front catalyst 32a and the rear catalyst 32b (step S2). For example, the ECU 100 may estimate the temperature of the front catalyst 32a based on the output value of the front temperature sensor 33a, and may estimate the temperature of the rear catalyst 32b based on the output value of the rear temperature sensor 33b. The ECU 100 may estimate the temperatures of the front catalyst 32a and the rear catalyst 32b based on an integrated value of the intake air amount and the fuel injection amount. Step S2 is an example of a process executed by the acquisition unit.

[0018] Next, the ECU 100 acquires the oxygen storage capacity of each of the front catalyst 32a and the rear catalyst 32b (step S3). The oxygen storage capacity of the front catalyst 32a is estimated based on an integrated value of the amount of oxygen in the exhaust gas discharged from the front catalyst 32a while control is being executed in which the target air-fuel ratio in the engine body 10 is periodically alternately switched between a rich air-fuel ratio and a lean air-fuel ratio. Similarly, the oxygen storage capacity of the rear catalyst 32b is estimated based on an integrated value of the amount of oxygen in the exhaust gas discharged from the rear catalyst 32b while control is being executed in which the target air-fuel ratio in the engine body 10 is periodically alternately switched between a rich air-fuel ratio and a lean air-fuel ratio. The amount of oxygen in the exhaust gas discharged from the front catalyst 32a can be calculated based on the output value of an oxygen concentration sensor or an air-fuel ratio sensor arranged between the front catalyst 32a and the rear catalyst 32b. The amount of oxygen in the exhaust gas discharged from the rear catalyst 32b can be calculated based on the output value of an oxygen concentration sensor or an air-fuel ratio sensor arranged downstream of the rear catalyst 32b. Step S3 is an example of a process executed by the acquisition unit.

[0019] Next, the ECU 100 determines whether the NOx sensor 34 is activated (step S4). The NOx sensor 34 is activated when the NOx sensor 34 is heated to an appropriate temperature and the output value of the NOx sensor 34 is appropriate. For example, the ECU 100 may determine that the NOx sensor 34 is activated by exhaust heat after a predetermined time has elapsed since the start of the engine 1. If the result in step S4 is No, this control ends.

[0020] If the answer is Yes in step S4, the ECU 100 determines whether or not there is an ammonia component in the exhaust gas (step S5). For example, as described in the above-mentioned JP 2023-003623 A, it is possible to determine whether or not there is an ammonia component in the exhaust gas based on the direction of the current flowing through the pump cell and the sensor cell of the NOx sensor 34. If the answer is No in step S5, this control ends.

[0021] Next, the ECU 100 determines whether or not the temperature of the front-stage catalyst 32a acquired in step S2 is equal to or higher than temperature A (step S6). Temperature A is the temperature at which the production of ammonia begins in the front-stage catalyst 32a. If the result in step S6 is No, this control ends.

[0022] If the answer is Yes in step S6, the ECU 100 determines whether the temperature of the rear catalyst 32b acquired in step S2 is equal to or higher than temperature B (step S7). Temperature B is the temperature at which the production of ammonia begins in the rear catalyst 32b. Temperature B may be the same value as temperature A, or may be a different value.

[0023] If the answer is No in step S7, it is assumed that ammonia is generated in the front catalyst 32a and that ammonia is not generated in the rear catalyst 32b. In this case, the ECU 100 refers to the map in Fig. 3A and calculates the ammonia ratio based on the temperature of the front catalyst 32a and the oxygen storage capacity of the front catalyst 32a (step S8). The ammonia ratio is the ratio of the ammonia concentration to the output value of the NOx sensor 34. The higher the ammonia ratio, the lower the NOx ratio of the NOx concentration to the output value of the NOx sensor 34.

[0024] Fig. 3A is an example of a map that defines the ammonia ratio according to the temperature and oxygen storage capacity of the front-stage catalyst 32a. In Fig. 3A, the horizontal axis indicates the temperature of the front-stage catalyst 32a, and the vertical axis indicates the ammonia ratio. The ammonia ratio is defined to be between 0 and 100%. As shown in Fig. 3A, the higher the temperature of the front-stage catalyst 32a is above temperature A, and the greater the oxygen storage capacity of the front-stage catalyst 32a, the greater the ammonia ratio. As described above, the oxygen storage capacity correlates with the performance of the catalyst. This is because the higher the oxygen storage capacity, the higher the catalyst performance and the greater the amount of ammonia generated by the catalyst.

[0025] If the answer is Yes in step S7, the ECU 100 refers to the map in Fig. 3B and calculates the ammonia ratio based on the temperature and the oxygen storable amount of the rear catalyst 32b (step S9). Fig. 3B is an example of a map that defines the ammonia ratio according to the temperature and the oxygen storable amount of the rear catalyst 32b. As in Fig. 3A, in Fig. 3B, the ammonia ratio increases as the temperature of the rear catalyst 32b is higher than temperature B and as the oxygen storable amount of the rear catalyst 32b increases. Steps S8 and S9 are an example of processing executed by the calculation unit.

[0026] Next, the ECU 100 acquires an output value of the NOx sensor 34 (step S10). Step S10 is an example of a process executed by the acquisition unit.

[0027] Next, the ECU 100 calculates the ammonia concentration in the exhaust gas (step S11) based on the ammonia ratio calculated in step S8 or S9 and the output value of the NOx sensor 34. Specifically, the ammonia concentration is calculated based on the following formula. Ammonia concentration=output value of NOx sensor 34×(1-(ammonia ratio / 100)) Step S11 is an example of a process executed by the calculation unit.

[0028] As described above, the concentration of ammonia in the exhaust gas can be calculated with high accuracy based on the temperature of either the front catalyst 32a or the rear catalyst 32b, the oxygen storable amount, and the output value of the NOx sensor .

[0029] The reason for not executing step S7 when step S6 is No is that the front catalyst 32a is closer to the engine body 10 and is more likely to become hotter than the rear catalyst 32b, and when the temperature of the front catalyst 32a is below temperature A, the temperature of the rear catalyst 32b is often also below temperature B. In the above embodiment, two catalysts, the front catalyst 32a and the rear catalyst 32b, are provided, but this is not limiting and only one catalyst may be provided.

[0030] Although a preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0031] 1 Engine 30 Exhaust passage 32a Front stage catalyst (catalyst) 32b Rear catalyst (catalyst) 34 NOx sensor 100 ECU (ammonia concentration calculation device, acquisition unit, calculation unit)

Claims

[Claim 1] an acquisition unit that acquires a temperature of a catalyst disposed in an exhaust passage of an internal combustion engine, an oxygen storage capacity of the catalyst, and an output value of a NOx sensor disposed downstream of the catalyst in the exhaust passage; a calculation unit that calculates a concentration of ammonia in exhaust gas flowing downstream of the catalyst based on the temperature, the oxygen storable amount, and the output value.

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