Catalyst temperature calculation device

Abstract

Provided is a catalyst temperature calculation device capable of calculating the temperature of a three-way catalyst having an oxygen storage capability with high accuracy. This catalyst temperature calculation device is provided with: an estimation unit that estimates, on the basis of the amount of heat of exhaust gas discharged from an engine, the temperature of a three-way catalyst that has oxygen storage capacity and purifies the exhaust gas from the engine; and a correction unit that corrects the temperature of the three-way catalyst estimated by the estimation unit on the basis of the ammonia concentration in the exhaust gas discharged from the three-way catalyst into which the exhaust gas having a rich air-fuel ratio flows.

Description

Technical Field

[0001] This 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 of the exhaust gas discharged from the engine (e.g., see Patent Document 1).

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2010-265786. Summary of the Invention The problem that the invention aims to solve

[0004] The temperature of the catalyst is affected not only by the heat from the exhaust gas, but also by the ambient temperature and heat dissipation into the exhaust passage. Therefore, relying solely on the heat from the exhaust gas may not be sufficient to accurately calculate the catalyst temperature.

[0005] Therefore, the objective is to provide a catalyst temperature calculation device capable of calculating the temperature of a three-way catalyst with oxygen storage capacity with high precision. Methods for solving problems

[0006] The above objective can be achieved by the following catalyst temperature calculation device, which includes: an estimation unit that estimates the temperature of a three-way catalyst having oxygen storage capacity and purifying the exhaust gas from the engine based on the heat of the exhaust gas discharged 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 the exhaust gas discharged from the three-way catalyst that flows into the exhaust gas with a rich air-fuel ratio. Invention Effects

[0007] A catalyst temperature calculation device is provided that can calculate the temperature of a three-way catalyst with oxygen storage capacity with high precision. Attached Figure Description

[0008] Figure 1 It is a schematic diagram of the engine system. Figure 2 This is a flowchart illustrating the calculation and control of catalyst temperature. Figure 3 This is a flowchart illustrating intermittent engine stop control. Detailed Implementation

[0009] [Simplified structure of the catalyst temperature calculation device] Figure 1This is a schematic structural diagram of engine system 1. Engine system 1 can be mounted on, for example, a vehicle, but is not limited to this; it can also be mounted on other types of equipment such as ships. Engine system 1 includes an engine 10 and an exhaust passage 20. Engine 10 is a multi-cylinder engine with multiple cylinders. Engine 10 is equipped with spark plugs and in-cylinder injection valves. In addition, engine 10 is connected to an intake passage (not shown).

[0010] The exhaust passage 20 includes an exhaust manifold 21 connected to the engine 10 and an exhaust pipe 22 located downstream of the exhaust manifold 21. An upstream catalyst (S / C) 31 is disposed between the exhaust manifold 21 and the exhaust pipe 22. A downstream catalyst (U / F) 32 is disposed in the exhaust pipe 22. An upstream air-fuel ratio sensor 41 is disposed at the confluence of the branches of the exhaust manifold 21 that connect to each cylinder. A downstream air-fuel ratio sensor 42 is disposed in the exhaust pipe 22 downstream of the upstream catalyst 31. A NOx sensor 43 is disposed 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 flowing into the upstream catalyst 31. The downstream air-fuel ratio sensor 42 detects the air-fuel ratio of the exhaust exiting from the upstream catalyst 31 and flowing into the downstream catalyst 32. The output value of the NOx sensor 43 is correlated with the NOx concentration in the exhaust under lean atmosphere conditions and with the ammonia concentration in the exhaust under rich atmosphere conditions.

[0011] The upstream catalyst 31 and downstream catalyst 32 are three-way catalysts containing catalyst metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and possessing oxygen storage capacity. Due to their catalytic action and oxygen storage capacity, the three-way catalyst purifies NOx and HC depending on the amount of oxygen stored. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, oxygen in the exhaust gas is stored through the catalyst when the oxygen storage capacity is low. Simultaneously, NOx in the exhaust gas is reduced and purified. When the oxygen storage capacity in the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust gas flowing out of the catalyst increase. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich, the oxygen stored in the catalyst is released when the oxygen storage capacity is high, and HC in the exhaust gas is oxidized and purified. When the oxygen storage capacity in the three-way catalyst decreases, the concentration of HC in the exhaust gas flowing out of the catalyst increases. Furthermore, ammonia is generated from NOx in the three-way catalyst.

[0012] Here, the ammonia generated in the three-way catalyst is produced in a rich atmosphere through the following reaction. N2 + 3H2 → 2NH3 + (heat reaction) Therefore, the lower the temperature of the three-way catalyst, the more the exothermic reaction is promoted, and the more ammonia is produced. Furthermore, 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, thus increasing the amount of ammonia produced.

[0013] The ECU (Electronic Control Unit) 50 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read-Only Memory), and flash memory, and performs various controls by executing programs stored in the ROM and other memory devices. The ECU 50 controls the engine 10 based on the driver's input to the accelerator and brake pedals, the engine speed, and the load. 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 are input to the ECU 50. The ECU 50 is an example of a catalyst temperature calculation device, which will be described in detail later. Functionally, the ECU 50 implements the estimation and correction units described in detail later.

[0014] ECU 50 controls the target air-fuel ratio of the exhaust gas discharged from engine 10, alternating between a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio (e.g., 14.6) and a lean air-fuel ratio larger than the stoichiometric air-fuel ratio. Specifically, ECU 50 controls the air-fuel ratio of the exhaust gas discharged from engine 10 so that the air-fuel ratio detected by upstream air-fuel ratio sensor 41 becomes the target air-fuel ratio. Specifically, based on the air-fuel ratio detected by upstream air-fuel ratio sensor 41 and downstream air-fuel ratio sensor 42, ECU 50 mainly controls the air-fuel ratio of the exhaust gas discharged from engine 10 through feedback control of the fuel injection quantity.

[0015] [Catalyst Temperature Calculation and Control] This describes the catalyst temperature calculation and control performed by ECU50. The temperature calculation for this control is applied to the downstream catalyst 32. Figure 2 This is a flowchart illustrating catalyst temperature calculation and control. ECU 50 determines whether the operating state of engine 10 is in a state where the temperature of downstream catalyst 32 is decreasing (step S1). A state where the temperature of downstream catalyst 32 is decreasing includes, for example, prolonged idling due to prolonged parking, prolonged fuel cut-off while driving downhill, and prolonged intermittent stopping of engine 10 in a hybrid vehicle. When the result in step S1 is "No", this control ends.

[0016] When "Yes" is selected in step S1, the ECU 50 estimates the temperature of the downstream catalyst 32 based on the heat of the exhaust gas (step S2). The estimation of the temperature of the downstream catalyst 32 can be performed using, for example, a known method described in Japanese Patent Application Publication No. 2010-265786. Alternatively, the heat transfer to the downstream catalyst 32 can be estimated from the heat transfer from the engine 10 to the exhaust port, exhaust passage 20, and upstream catalyst 31, and the temperature of the downstream catalyst 32 can be estimated based on this heat transfer. Furthermore, the temperature of the downstream catalyst 32 can also be estimated using known methods. Step S2 is an example of the process performed by the estimation unit.

[0017] Next, ECU50 determines whether the estimated temperature of the downstream catalyst 32 is lower than a threshold (step S3). This threshold is set as an upper limit temperature that ensures the accuracy of temperature correction based on the ammonia concentration described later. As mentioned above, the lower the temperature of the downstream catalyst 32, the greater the amount of ammonia generated in the downstream catalyst 32; therefore, the lower the temperature of the downstream catalyst 32, the higher the accuracy of temperature correction based on the ammonia concentration. If "No" is received in step S3, this control process ends.

[0018] When "Yes" is selected in step S3, the ECU 50 sets the target air-fuel ratio of the engine 10 to a rich air-fuel ratio (step S4). Thus, after the upstream catalyst 31 is in an oxygen-depleted state, 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 corrects the estimated temperature of the downstream catalyst 32 based on the ammonia concentration, thereby calculating the temperature of the downstream catalyst 32 (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 can be corrected by multiplying a correction factor (less than 1 and greater than 0, which decreases with higher ammonia concentration) by the estimated temperature of the downstream catalyst 32 based on the heat of the exhaust. Alternatively, the temperature of the downstream catalyst 32 can be estimated based on the ammonia concentration, and the average value of the estimated temperature of the downstream catalyst 32 based on the heat of the exhaust can be calculated, thereby correcting the temperature of the downstream catalyst 32. As described above, the estimated temperature of the downstream catalyst 32 based on the heat of the exhaust is corrected based on the ammonia concentration, thus enabling the calculation of the temperature of the downstream catalyst 32 with high accuracy. Step S6 is an example of the processing performed by the correction unit.

[0020] [Engine Intermittent Stop Control] Next, the intermittent stop control of the engine 10, including the catalyst temperature calculation and control described above, will be explained. Figure 3 This is a flowchart illustrating intermittent engine stop control. ECU 50 determines if there is an intermittent stop request from engine 10 (step S1a). If step S1a is "No", this control ends. If step S1a is "Yes", steps S2 and S3 described above are executed. If step S3 is "No", ECU 50 executes the intermittent stop of engine 10 (step S9). If step S3 is "Yes", 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 an upper limit at which the temperature of the downstream catalyst 32 is expected to drop significantly below the activation temperature due to the intermittent shutdown of the engine 10. When "yes" is received in step S7, this control ends. That is, the intermittent shutdown of the engine 10 is not performed. Thus, the significant drop in temperature of the downstream catalyst 32 due to the intermittent shutdown is suppressed.

[0022] When the answer in step S7 is "No", the ECU 50 sets the intermittent stop time of the engine 10 to be shorter as the calculated temperature of the downstream catalyst 32 decreases (step S8). Then, the ECU 50 executes the intermittent stop of the engine 10 for the set intermittent stop time (step S9). This suppresses a significant drop in the temperature of the downstream catalyst 32 and achieves intermittent stop of the engine 10. As described above, the ability to execute intermittent stop of the engine 10 and the intermittent stop time are set based on a highly accurate calculated temperature of the downstream catalyst 32. This suppresses a significant drop in the temperature of the downstream catalyst 32 and ensures the enforceability of intermittent stop of the engine 10.

[0023] Alternatively, an ammonia sensor can be used to detect ammonia concentration instead of the NOx sensor 43 used in the above embodiments, but considering cost, it is preferable to use the existing NOx sensor 43.

[0024] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to these specific embodiments. Various modifications and alterations can be made within the scope of the spirit of the present invention as set forth in the claims. Explanation of reference numerals in the attached figures

[0025] 10 Engines 32 Downstream catalysts (three-way catalysts) 43 NOx Sensor 50 ECU (Catalyst Temperature Calculation Unit, Estimation Unit, Correction Unit).

Claims

1. A catalyst temperature calculation device, comprising: The estimation section estimates the temperature of a three-way catalytic converter that has oxygen storage capacity and purifies the exhaust gas from the engine, based on the heat from the exhaust gas discharged from the engine; and The correction section corrects the temperature of the three-way catalyst estimated by the estimation section based on the ammonia concentration in the exhaust gas discharged from the three-way catalyst that flows into the exhaust gas with a rich air-fuel ratio.

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