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 Art

[0002] Patent Document 1 describes the relationship between the temperature of a catalyst and the amount of ammonia generated by 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

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

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

[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 Problems

[0006] The above objective can be achieved by an ammonia concentration calculation device comprising: an acquisition unit that acquires the temperature of a catalyst placed in the exhaust passage of an internal combustion engine, the oxygen storage capacity of the catalyst, and the output value of a NOx sensor placed downstream of the catalyst in the exhaust passage; and a calculation unit that calculates the concentration of ammonia in the exhaust flowing downstream of the catalyst based on the temperature, the oxygen storage capacity, and the output value. [Effects of the Invention]

[0007] We can provide an ammonia concentration calculation device that can accurately calculate the concentration of ammonia in exhaust gas. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the engine's configuration. [Figure 2] Figure 2 is a flowchart illustrating the control of ammonia concentration calculation. [Figure 3] Figure 3A is an example of a map that defines the ammonia ratio according to the temperature and oxygen storage capacity of the upstream catalyst, and Figure 3B is an example of a map that defines the ammonia ratio according to the temperature and oxygen storage capacity of the downstream catalyst. [Modes for carrying out the invention]

[0009] [Overall configuration of Engine 1] Figure 1 is a schematic diagram of the engine 1. Engine 1 is mounted on a vehicle, for example, but is not limited to this and may be mounted on ships or other vessels. Engine 1 is an example of an internal combustion engine, for example, a gasoline engine, but may also be a diesel engine. 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 multiple cylinders, and each cylinder is provided with a combustion chamber 11, a piston 12, a spark plug 16, etc. Inside the engine body 10 are a connecting rod 13 and a crankshaft 14. The piston 12 is connected to the crankshaft 14 by the connecting rod 13. The engine body 10 is provided with a rotational speed sensor 15, and an in-cylinder injection valve 17 is provided for each cylinder. The rotational speed sensor 15 detects the rotational speed of the engine body 10 by detecting the rotational speed of the crankshaft 14. The in-cylinder injection valve 17 directly injects fuel into the combustion chamber 11. Alternatively, instead of the in-cylinder injection valve 17, a port injection valve that injects fuel towards the intake port of the engine body 10 may be provided, 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. The intake port and exhaust port of the engine body 10 are connected to an intake passage 20 and an exhaust passage 30, respectively. The intake valve 18a and exhaust valve 18b open and close the intake port and exhaust port of the engine body 10, respectively.

[0010] The intake passage 20 is equipped with an air cleaner 21, an air flow meter 22, and a throttle valve 23, in 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 obtains the intake air volume. The throttle valve 23 is driven by an actuator (not shown), for example, to adjust the intake air volume.

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

[0012] The exhaust passage 30 is equipped with, in order from upstream to downstream, an upstream catalyst 32a, an upstream temperature sensor 33a, a downstream catalyst 32b, a downstream temperature sensor 33b, and a NOx sensor 34. The upstream temperature sensor 33a detects the temperature of the exhaust gas discharged from the upstream catalyst 32a and flowing into the downstream catalyst 32b. The downstream temperature sensor 33b detects the temperature of the exhaust gas discharged from the downstream catalyst 32b. The NOx sensor 34 detects the concentration of NOx in the exhaust gas discharged from the downstream 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 possess oxygen storage capacity. The three-way catalyst, through its catalytic action and oxygen storage capacity, purifies NOx and HC depending on the amount of oxygen stored. Specifically, when the air-fuel ratio of the exhaust flowing into the three-way catalyst is lean, oxygen is absorbed from the exhaust by the catalyst when its oxygen storage capacity is low. Consequently, NOx in the exhaust is reduced and purified. As the oxygen storage capacity of the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust flowing out of the catalyst rise. When the air-fuel ratio of the exhaust flowing into the three-way catalyst is rich, oxygen stored in the catalyst is released when its oxygen storage capacity is high, and HC in the exhaust is oxidized and purified.

[0014] When exhaust gas containing HC, CO, and water flows into such a three-way catalyst, hydrogen is produced through catalytic action. When NOx in the exhaust reacts with hydrogen, ammonia is produced. 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 more ammonia is produced. The performance of the three-way catalyst correlates with the oxygen storage capacity. As the service period of the three-way catalyst lengthens, its performance deteriorates, and the oxygen storage capacity also decreases.

[0015] The ECU (Electric Control Unit) 100 is equipped with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and memory devices such as flash memory, and performs various controls by executing programs stored in the ROM and memory devices. The ECU 100 controls the spark plug 16, in-cylinder injection valve 17, and throttle valve 23 based on the amount of operation of the accelerator pedal and brake pedal operated by the driver, the rotational speed and load of the engine body 10, etc. The ECU 100 receives input such as the rotational speed detected by the rotational speed sensor 15, the intake air amount detected by the airflow 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. Furthermore, the acquisition unit and calculation unit described later are functionally realized in the ECU 100 by the CPU, RAM, ROM, and memory devices described above.

[0016] [Ammonia concentration calculation control] Figure 2 is a flowchart illustrating ammonia concentration calculation control. This control is repeatedly executed when the ignition is ON. The ECU 100 determines whether or not engine 1 has started (step S1). If the answer in step S1 is No, this control terminates.

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

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

[0019] Next, the ECU 100 determines whether the NOx sensor 34 is activated (step S4). Whether the NOx sensor 34 is activated means that the NOx sensor 34 is heated to an appropriate temperature so that 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 answer is No in step S4, this control ends.

[0020] If the answer in step S4 is Yes, the ECU 100 determines whether there is an ammonia component in the exhaust (step S5). For example, as described in Japanese Patent Application Laid-Open No. 2023-003623 mentioned above, based on the directions of the currents flowing through the pump cell and the sensor cell of the NOx sensor 34, it is possible to determine whether the exhaust contains an ammonia component. If the answer in step S5 is No, this control ends.

[0021] Next, the ECU 100 determines whether the temperature of the upstream catalyst 32a obtained in step S2 is equal to or higher than temperature A (step S6). Temperature A is the temperature at which ammonia generation starts in the upstream catalyst 32a. If the answer in step S6 is No, this control ends.

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

[0023] If the answer in step S7 is No, it is considered that ammonia is generated in the upstream catalyst 32a but not in the downstream 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 upstream catalyst 32a and the oxygen storage capacity of the upstream 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] Figure 3A is an example of a map that defines the ammonia ratio according to the temperature and oxygen storage capacity of the pre-catalyst 32a. In Figure 3A, the horizontal axis represents the temperature of the pre-catalyst 32a, and the vertical axis represents the ammonia ratio. The ammonia ratio is defined between 0 and 100%. As shown in Figure 3A, the higher the temperature of the pre-catalyst 32a (above temperature A) and the greater the oxygen storage capacity of the pre-catalyst 32a, the greater the ammonia ratio. As mentioned above, the oxygen storage capacity correlates with the performance of the catalyst. This is because a higher oxygen storage capacity leads to higher catalyst performance and an increase in the amount of ammonia produced by the catalyst.

[0025] If the answer in step S7 is Yes, the ECU 100 refers to the map in Figure 3B and calculates the ammonia ratio based on the temperature and oxygen storage capacity of the downstream catalyst 32b (step S9). Figure 3B is an example of a map that defines the ammonia ratio according to the temperature and oxygen storage capacity of the downstream catalyst 32b. Similar to Figure 3A, in Figure 3B the higher the temperature of the downstream catalyst 32b (above temperature B) and the greater the oxygen storage capacity of the downstream catalyst 32b, the higher the ammonia ratio. Steps S8 and S9 are examples of processes performed by the calculation unit.

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

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

[0028] As described above, the ammonia concentration in the exhaust gas can be accurately calculated based on the temperature of either the upstream catalyst 32a or the downstream catalyst 32b, the oxygen storage capacity, and the output value of the NOx sensor 34.

[0029] Furthermore, the reason why step S7 is not performed if the answer in step S6 is No is that the pre-catalyst 32a is closer to the engine body 10 and therefore more prone to high temperatures than the post-catalyst 32b, and if the temperature of the pre-catalyst 32a is below temperature A, the temperature of the post-catalyst 32b is often also below temperature B. In the above embodiment, two catalysts, the pre-catalyst 32a and the post-catalyst 32b, are provided, but the invention is not limited to this, and only one catalyst may be provided.

[0030] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0031] 1 Engine 30 Exhaust passage 32a Front stage catalyst (catalyst) 32b Post-stage catalytic converter (catalyst) 34 NOx Sensors 100 ECU (Ammonia concentration calculation device, acquisition unit, calculation unit)

Claims

[Claim 1] An acquisition unit that acquires the temperature of a catalyst located in the exhaust passage of an internal combustion engine, the oxygen storage capacity of the catalyst, and the output value of a NOx sensor located downstream of the catalyst in the exhaust passage, The system includes a calculation unit that calculates the concentration of ammonia in the exhaust gas flowing downstream of the catalyst based on the temperature, the oxygen storage capacity, and the output value. The oxygen storage capacity is estimated based on the cumulative amount of oxygen in the exhaust gas emitted from the catalyst while the engine body of the internal combustion engine is being controlled to periodically switch between a rich air-fuel ratio and a lean air-fuel ratio. The amount of oxygen in the exhaust gas discharged from the catalyst is calculated based on the output value of an oxygen concentration sensor or an air-fuel ratio sensor located downstream of the catalyst. The ammonia concentration is calculated based on the formula: output value × (1 - (ammonia percentage / 100)). The ammonia ratio is the percentage of the ammonia concentration relative to the output value, and is defined as being between 0 and 100%. An ammonia concentration calculation device that calculates the ammonia ratio such that the higher the temperature is above a predetermined temperature and the greater the amount of oxygen that can be absorbed, the higher the ammonia ratio will be.

Images