Catalyst temperature calculation device

Abstract

To provide a catalyst temperature calculation device capable of accurately calculating the temperature of a three way catalyst having oxygen storage capacity.SOLUTION: A catalyst temperature calculation device comprising: an estimation unit configured to estimate a temperature of a three way catalyst that has an oxygen storage capacity and purifies exhaust gas from an engine, based on a heat quantity of the exhaust gas discharged from the engine; and a correction unit configured to correct the temperature of the three way catalyst estimated by the estimation unit, based on an ammonia concentration in exhaust gas discharged from the three way catalyst into which exhaust gas having a rich air-fuel ratio flows.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a catalyst temperature calculation device. [Background technology]

[0002] There is a technique for calculating the temperature of a catalyst that purifies exhaust gas from an engine based on the heat quantity of the exhaust gas emitted from the engine (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-265786 Summary of the Invention [Problem to be solved by the invention]

[0004] The catalyst temperature is affected not only by the heat quantity of the exhaust gas, but also by the outside temperature and heat radiation into the exhaust passage. For this reason, it may not be possible to accurately calculate the catalyst temperature based on the heat quantity of the exhaust gas alone.

[0005] Therefore, an object of the present invention is to provide a catalyst temperature calculation device that can accurately calculate the temperature of a three-way catalyst having oxygen storage capacity. [Means for solving the problem]

[0006] The above object can be achieved by a catalyst temperature calculation device including: an estimation unit that estimates the temperature of a three-way catalyst that has oxygen storage capacity and purifies exhaust gas from an engine, based on the heat quantity of the exhaust gas emitted from the engine; and a correction unit that corrects the temperature of the three-way catalyst estimated by the estimation unit, based on the ammonia concentration in exhaust gas emitted from the three-way catalyst into which exhaust gas with a rich air-fuel ratio has flowed. [Effects of the Invention]

[0007] It is possible to provide a catalyst temperature calculation device that can accurately calculate the temperature of a three-way catalyst having oxygen storage capacity. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic configuration diagram of an engine system. [Figure 2] 4 is a flowchart illustrating a catalyst temperature calculation control. [Figure 3] 4 is a flowchart illustrating an example of engine intermittent stop control. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Schematic configuration of catalyst temperature calculation device] FIG. 1 is a schematic diagram of an engine system 1. The engine system 1 is mounted on, for example, a vehicle, but is not limited thereto and may also be mounted on a vessel or other vehicle. The engine 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 a spark 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 output value of the NOx sensor 43 correlates with the NOx concentration in the exhaust gas in a lean atmosphere, and correlates with the ammonia concentration in the exhaust gas in a rich atmosphere.

[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, ammonia is produced from NOx using a three-way catalyst.

[0012] Here, ammonia produced in the three-way catalyst is produced by the following reaction in a rich atmosphere. N2+3H2→2NH3+reaction heat Therefore, the lower the temperature of the three-way catalyst, the more the heat of reaction is dissipated, and the more ammonia is produced. Also, the higher the pressure of the exhaust gas flowing into the three-way catalyst, the more the reaction proceeds in the direction of decreasing the total number of molecules, and the more ammonia is produced.

[0013] The ECU (Electric Control Unit) 50 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), 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 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 catalyst temperature calculation device, which will be described in detail later. The ECU 50 functionally realizes an estimation unit and a correction unit, which will be described in detail later.

[0014] 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 mainly by feedback controlling the fuel injection amount based on the air-fuel ratios detected by the upstream air-fuel ratio sensor 41 and the downstream air-fuel ratio sensor 42.

[0015] [Catalyst temperature calculation control] The catalyst temperature calculation control executed by the ECU 50 will now be described. The target of the temperature calculation by the catalyst temperature calculation control is the downstream catalyst 32. FIG. 2 is a flowchart illustrating the catalyst temperature calculation control. The ECU 50 determines whether the operating state of the engine 10 is such that the temperature of the downstream catalyst 32 will drop (step S1). Examples of states in which the temperature of the downstream catalyst 32 will drop include when the vehicle is stopped for a long period of time and idles for a long period of time, when traveling downhill and fuel is cut for a long period of time, or when the engine 10 is intermittently stopped for a long period of time in a hybrid vehicle. If the answer is No in step S1, this control ends.

[0016] If the answer is Yes in step S1, the ECU 50 estimates the temperature of the downstream catalyst 32 based on the heat quantity of the exhaust gas (step S2). The temperature of the downstream catalyst 32 may be estimated using a known method, for example, as described in Japanese Patent Application Laid-Open No. 2010-265786. Alternatively, the amount of heat transferred to the downstream catalyst 32 may be estimated taking into account the amount of heat transferred from the engine 10 to the exhaust port, the exhaust passage 20, and the upstream catalyst 31, and the temperature of the downstream catalyst 32 may be estimated based on the amount of heat transferred to the downstream catalyst 32. Alternatively, the temperature of the downstream catalyst 32 may be estimated using a known method. Step S2 is an example of processing executed by the estimation unit.

[0017] Next, the ECU 50 determines whether the estimated temperature of the downstream catalyst 32 is below a threshold value (step S3). Here, the threshold value is set to an upper limit temperature that can ensure accuracy in correcting the temperature of the downstream catalyst 32 based on the ammonia concentration, which will be described later. As described above, the lower the temperature of the downstream catalyst 32, the greater the amount of ammonia produced in the downstream catalyst 32. Therefore, the lower the temperature of the downstream catalyst 32, the more accurate the correction of the temperature of the downstream catalyst 32 based on the ammonia concentration. If the determination in step S3 is No, this control ends.

[0018] If the answer to step S3 is Yes, the ECU 50 sets the target air-fuel ratio of the engine 10 to a rich air-fuel ratio (step S4). As a result, after the upstream catalyst 31 becomes oxygen-starved, exhaust gas with a rich air-fuel ratio flows into the downstream catalyst 32. Next, the ECU 50 obtains the ammonia concentration in the exhaust gas discharged from the downstream catalyst 32 based on the output value of the NOx sensor 43 (step S5).

[0019] Next, the ECU 50 calculates the temperature of the downstream catalyst 32 by correcting the temperature of the downstream catalyst 32 estimated based on the ammonia concentration (step S6). As described above, the higher the ammonia concentration, the lower the estimated temperature of the downstream catalyst 32. Therefore, for example, the temperature of the downstream catalyst 32 may be corrected by multiplying the temperature of the downstream catalyst 32 estimated based on the heat quantity of the exhaust gas by a correction coefficient that is equal to or smaller than 1 and greater than 0, and that decreases as the ammonia concentration increases. Alternatively, the temperature of the downstream catalyst 32 may be estimated based on the ammonia concentration, and the temperature of the downstream catalyst 32 may be corrected by calculating the average value of the temperature of the downstream catalyst 32 estimated based on the ammonia concentration and the temperature of the downstream catalyst 32 estimated based on the heat quantity of the exhaust gas. As described above, the temperature of the downstream catalyst 32 estimated based on the heat quantity of the exhaust gas is corrected based on the ammonia concentration, so the temperature of the downstream catalyst 32 is calculated with high accuracy. Step S6 is an example of processing executed by the correction unit.

[0020] [Engine intermittent stop control] Next, the intermittent stop control of the engine 10, including the above-mentioned catalyst temperature calculation control, will be described. Fig. 3 is a flowchart illustrating the intermittent stop control of the engine. The ECU 50 determines whether or not there is a request to intermittently stop the engine 10 (step S1a). If the answer is No in step S1a, this control ends. If the answer is Yes in step S1a, the above-mentioned steps S2 and S3 are executed. If the answer is No in step S3, the ECU 50 executes the intermittent stop of the engine 10 (step S9). If the answer is Yes in step S3, steps S4 to S6 are executed.

[0021] Next, the ECU 50 determines whether the calculated temperature of the downstream catalyst 32 is lower than a predetermined temperature (step S7). The predetermined temperature is set to the upper limit of the temperature at which the temperature of the downstream catalyst 32 is predicted to drop significantly below the activation temperature due to the execution of intermittent stopping of the engine 10. If the determination in step S7 is Yes, this control ends. That is, the intermittent stopping of the engine 10 is not executed. This prevents the temperature of the downstream catalyst 32 from dropping significantly due to the execution of intermittent stopping.

[0022] If the answer is No in step S7, the ECU 50 sets the intermittent stop time for the engine 10 to a shorter time as the calculated temperature of the downstream catalyst 32 is lower (step S8). Next, the ECU 50 executes intermittent stop of the engine 10 for the set intermittent stop time (step S9). This achieves intermittent stop of the engine 10 while preventing a large drop in the temperature of the downstream catalyst 32. As described above, whether or not to execute intermittent stop of the engine 10 and the intermittent stop time are set based on the accurately calculated temperature of the downstream catalyst 32. This ensures the feasibility of intermittent stop of the engine 10 while preventing a large drop in the temperature of the downstream catalyst 32.

[0023] Instead of the NOx sensor 43 used in the above embodiment, an ammonia sensor may be used to detect the ammonia concentration, but it is preferable to use the existing NOx sensor 43 in consideration of cost.

[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 described in the claims. [Explanation of symbols]

[0025] 10 Engine 32 Downstream catalyst (three-way catalyst) 43 NOx sensor 50 ECU (catalyst temperature calculation device, estimation section, correction section)

Claims

[Claim 1] an estimation unit that estimates a temperature of a three-way catalyst that has an oxygen storage capacity and purifies exhaust gas from the engine based on a heat quantity of exhaust gas discharged from the engine; a correction unit that corrects the temperature of the three-way catalyst estimated by the estimation unit based on an ammonia concentration in exhaust gas discharged from the three-way catalyst into which exhaust gas with a rich air-fuel ratio has flowed.

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