Engine System

Abstract

To provide an engine system which can control an oxygen supply amount to a filter and a second catalyst according to a state of the filter.SOLUTION: An engine system comprises: an engine main body; a first catalyst; a second catalyst located at a downstream side rather than the first catalyst; a filter arranged between the first catalyst and the second catalyst; a sensor arranged between the first catalyst and the filter, and detecting an air-fuel ratio; and a control device for controlling the air-fuel ratio to a target air-fuel ratio by controlling a fuel injection amount and a suction air amount. The control device comprises: an air-fuel ratio control part for switching the air-fuel ratio to a target rich air-fuel ratio which is lower than a theoretical air-fuel ratio from a lean air-fuel ratio when a detected air-fuel ratio becomes equal to or higher than a lean determination air-fuel ratio which is higher than the theoretical air-fuel ratio; an acquisition part for acquiring a temperature of the filter and an accumulation amount of exhaust particulates in the filter; and an oxygen supply amount control part for controlling an oxygen supply amount to the filter and the second catalyst by setting at least one of the lean determination air-fuel ratio and the target lean air-fuel ratio according to the temperature and the accumulation amount.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an engine system. [Background technology]

[0002] In some cases, a filter is provided between a first catalyst and a second catalyst that are respectively arranged upstream and downstream of an exhaust passage connected to an engine body (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-127559 Summary of the Invention [Problem to be solved by the invention]

[0004] The ideal amount of oxygen supplied to the filter and second catalyst varies depending on the condition of the filter. For example, if the amount of oxygen supplied is constant regardless of the condition of the filter, the filter may overheat or the purification capacity of the second catalyst may decrease.

[0005] Therefore, an object of the present invention is to provide an engine system that can control the amount of oxygen supplied to the filter and the second catalyst according to the state of the filter. [Means for solving the problem]

[0006] The object is to provide an engine having an engine body, an exhaust passage connected to the engine body, a first catalyst arranged in the exhaust passage and having oxygen storage capacity, a second catalyst arranged in the exhaust passage downstream of the first catalyst, a filter arranged in the exhaust passage between the first catalyst and the second catalyst, a sensor arranged in the exhaust passage between the first catalyst and the filter and detecting an air-fuel ratio of exhaust gas, and a control device that controls the air-fuel ratio of the engine body to a target air-fuel ratio by controlling a fuel injection amount and an intake air amount of the engine body, wherein the control device controls the sensor This can be achieved by an engine system including: an air-fuel ratio control unit that switches the target air-fuel ratio from a target lean air-fuel ratio that is higher than the stoichiometric air-fuel ratio to a target rich air-fuel ratio that is lower than the stoichiometric air-fuel ratio when the detected air-fuel ratio becomes equal to or higher than a lean judgment air-fuel ratio that is higher than the stoichiometric air-fuel ratio; an acquisition unit that acquires the temperature of the filter and the amount of accumulation of exhaust particulates on the filter; and an oxygen supply amount control unit that controls the amount of oxygen supplied to the filter and the second catalyst by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio in accordance with the temperature and the amount of accumulation.

[0007] In a first state in which the temperature is higher than a first temperature threshold and the deposition amount is larger than a first deposition amount threshold, the oxygen supply amount control unit reduces the oxygen supply amount by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio, compared to a reference state in which the temperature is equal to or lower than a reference temperature threshold and the deposition amount is equal to or lower than a reference deposition amount threshold, and the first temperature threshold may be higher than the reference temperature threshold and the first deposition amount threshold may be larger than the reference deposition amount threshold.

[0008] In a second state in which the temperature is higher than the second temperature threshold and equal to or lower than the first temperature threshold, and the deposition amount is greater than the second deposition amount threshold and equal to or lower than the first deposition amount threshold, the oxygen supply amount control unit increases the oxygen supply amount compared to the first state and decreases the oxygen supply amount compared to the reference state by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio, and the second temperature threshold may be lower than the first temperature threshold and higher than the reference temperature threshold, and the second deposition amount threshold may be smaller than the first deposition amount threshold and greater than the reference deposition amount threshold.

[0009] In a third state in which the temperature is higher than the reference temperature threshold and equal to or lower than the second temperature threshold and the deposition amount is greater than the reference deposition amount threshold and equal to or lower than the second deposition amount threshold, the oxygen supply amount control unit may increase the oxygen supply amount compared to the reference state by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio.

[0010] The acquisition unit may acquire an intake air amount of the engine body, and when the intake air amount of the engine in the third state is greater than an air amount threshold, the oxygen supply amount control unit may reduce the oxygen supply amount by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio, compared to when the intake air amount in the third state is equal to or less than the air amount threshold. [Effects of the Invention]

[0011] It is possible to provide an engine system that can control the amount of oxygen supplied to the filter and the second catalyst according to the state of the filter. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic configuration diagram of an engine system. [Figure 2] 4 is a timing chart illustrating the transition of the detected air-fuel ratio AFb. [Figure 3]10 is a view showing an example of a map that defines a lean judged air-fuel ratio LD that is set in accordance with the accumulation amount P of exhaust particulates accumulated on a filter and the temperature T of the filter. FIG. [Figure 4] 3 is a flowchart illustrating an example of air-fuel ratio control. [Figure 5] 4 is a timing chart illustrating the transition of the target air-fuel ratio TAF. [Figure 6] 10 is a view showing an example of a map that defines a lean target air-fuel ratio TL that is set in accordance with the accumulation amount P of exhaust particulates accumulated on a filter and the temperature T of the filter. FIG. [Figure 7] 10 is a flowchart illustrating a modified example of air-fuel ratio control. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Engine system overview] 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 other than a vehicle. The engine system 1 includes an engine body 10, an intake passage 20, and an exhaust passage 30. The engine body 10 is a gasoline engine, but may also be a diesel engine or a hydrogen engine. Each cylinder includes a combustion chamber 11, a piston 12, and an ignition plug 16. A connecting rod 13 and a crankshaft 14 are disposed 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. The engine body 10 also includes an in-cylinder injection valve 17 for each cylinder. The rotation speed sensor 15 detects the rotation speed of the crankshaft 14, thereby detecting the rotation speed of the engine body 10. The in-cylinder injection valve 17 directly injects fuel into the combustion chamber 11. The spark plug 16 ignites the air-fuel mixture in the combustion chamber 11. An intake passage 20 is connected to an intake port of the engine body 10. An exhaust passage 30 is connected to an exhaust port of the engine body 10. An intake valve 18a opens and closes the intake port of the engine body 10. An exhaust valve 18b opens and closes the exhaust port of the engine body 10.

[0014] 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 from the air flowing in from the outside. The air flow meter 22 acquires the intake air amount Ga. The throttle valve 23 adjusts the intake air amount Ga.

[0015] When intake valve 18a opens, air is introduced from intake passage 20 into combustion chamber 11. A mixture of fuel and air 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.

[0016] The exhaust passage 30 is provided with a first sensor 31a, a first catalyst 32a, a second sensor 31b, a filter 33, and a second catalyst 32b, arranged in this order from upstream to downstream. The first sensor 31a and the second sensor 31b are air-fuel ratio sensors that detect the air-fuel ratio of exhaust gas flowing through the exhaust passage 30. At least one of the first sensor 31a and the second sensor 31b may be an oxygen concentration sensor that can detect the air-fuel ratio of exhaust gas by detecting the oxygen concentration of the exhaust gas. The first sensor 31a detects the air-fuel ratio of exhaust gas discharged from the engine body 10 and flowing into the first catalyst 32a. The second sensor 31b detects the air-fuel ratio of exhaust gas discharged from the first catalyst 32a and flowing into the filter 33 and the second catalyst 32b. The filter 33 is a porous ceramic structure that captures exhaust particulates in the exhaust gas.

[0017] The first catalyst 32a and the second catalyst 32b are three-way catalysts containing catalytic metals, such as platinum (Pt), palladium (Pd), and rhodium (Rh), and have oxygen storage capacity. The three-way catalyst has catalytic action and oxygen storage capacity, and thus has the ability to purify NOx and HC according to the amount of oxygen stored. The second catalyst 32b does not necessarily have oxygen storage capacity.

[0018] The engine system 1 includes an ECU (Electric Control Unit) 100. The ECU 100 is equipped with a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a storage device. The ECU 100 performs various controls by executing programs stored in the ROM and the storage device. The ECU 100 controls the spark plugs 16, the in-cylinder injection valves 17, and the throttle valve 23 based on the amount of operation of the accelerator pedal and the brake pedal operated by the driver and the rotation speed and load of the engine main body 10. The ECU 100 receives detection values ​​from the rotation speed sensor 15, the air flow meter 22, the first sensor 31a, and the second sensor 31b. The ECU 100 also functionally realizes an air-fuel ratio control unit, an acquisition unit, and an oxygen supply amount control unit, which will be described later, by using the CPU, RAM, ROM, and storage device.

[0019] [Air-fuel ratio control] The ECU 100 controls the amount of fuel injection and intake air in the engine body 10, thereby controlling the air-fuel ratio of the exhaust gas discharged from the engine body 10 so that the detected air-fuel ratio AFa of the first sensor 31a becomes the target air-fuel ratio TAF. Specifically, the ECU 100 feedback-controls the amount of fuel injection from the direct injection valve 17 and the opening degree of the throttle valve 23 based on the detected air-fuel ratio AFa so that the detected air-fuel ratio AFa converges to the target air-fuel ratio TAF. In this way, the air-fuel ratio of the exhaust gas discharged from the engine body 10 is controlled to the target air-fuel ratio TAF. In detail, the air-fuel ratio is controlled as follows.

[0020] When the detected air-fuel ratio AFb of the second sensor 31b becomes the lean judged air-fuel ratio LD, the ECU 100 sets the target air-fuel ratio TAF to the rich target air-fuel ratio TR. When the detected air-fuel ratio AFb becomes the rich judged air-fuel ratio RD, the ECU 100 sets the target air-fuel ratio TAF to the lean target air-fuel ratio TL which is larger than the stoichiometric air-fuel ratio ST. Here, the lean judged air-fuel ratio LD is larger than the stoichiometric air-fuel ratio ST. The rich judged air-fuel ratio RD is smaller than the stoichiometric air-fuel ratio ST. The lean target air-fuel ratio TL is larger than the stoichiometric air-fuel ratio ST. The rich target air-fuel ratio TR is smaller than the stoichiometric air-fuel ratio ST. Therefore, the detected air-fuel ratio AFb periodically fluctuates between the lean judged air-fuel ratio LD and the rich judged air-fuel ratio RD. The above control is an example of processing executed by the air-fuel ratio control unit.

[0021] FIG. 2 is a timing chart illustrating the transition of the detected air-fuel ratio AFb. In this embodiment, the lean-determined air-fuel ratio LD is set to one of the air-fuel ratios LD0 to LD4. Of the air-fuel ratios LD0 to LD4, the air-fuel ratio LD1 is the smallest. The air-fuel ratio LD2 is greater than the air-fuel ratio LD1. The air-fuel ratio LD0 is greater than the air-fuel ratio LD2. The air-fuel ratio LD3 is greater than LD0. The air-fuel ratio LD4 is greater than the air-fuel ratio LD3. First, the transition of the detected air-fuel ratio AFb when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD0 will be described. When the detected air-fuel ratio AFb rises to the air-fuel ratio LD0, the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR (time t1). As a result, HC in the exhaust gas flowing into the first catalyst 32a is oxidized and purified by the oxygen stored in the first catalyst 32a. As a result, the detected air-fuel ratio AFb decreases from the lean side toward the stoichiometric air-fuel ratio ST. When the oxygen storage amount of the first catalyst 32a approaches zero, the oxygen concentration in the exhaust gas discharged from the first catalyst 32a decreases, and the detected air-fuel ratio AFb decreases toward the rich side.

[0022] When the detected air-fuel ratio AFb falls to the rich-determined air-fuel ratio RD, the target air-fuel ratio TAF is switched from a predetermined rich target air-fuel ratio TR to a predetermined lean target air-fuel ratio TL (time t2). As a result, oxygen in the exhaust gas flowing into the first catalyst 32a is stored in the first catalyst 32a, and NOx in the exhaust gas is reduced and purified. As a result, the detected air-fuel ratio AFb rises from the rich side toward the stoichiometric air-fuel ratio ST. When the amount of oxygen stored in the first catalyst 32a increases, the oxygen concentration in the exhaust gas discharged from the first catalyst 32a rises, and the detected air-fuel ratio AFb rises to the lean side.

[0023] 2 shows detected air-fuel ratios AFb1 to AFb4 when the lean judged air-fuel ratio LD is set to each of the air-fuel ratios LD1 to LD4. When the detected air-fuel ratio AFb1 rises to the air-fuel ratio LD1, the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR. Similarly, when the detected air-fuel ratio AFb2 rises to the air-fuel ratio LD2, when the detected air-fuel ratio AFb3 rises to the air-fuel ratio LD3, and when the detected air-fuel ratio AFb4 rises to the air-fuel ratio LD4, the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR.

[0024] The larger the set lean-determined air-fuel ratio LD, the later the time at which the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR. As a result, the larger the set lean-determined air-fuel ratio LD, the larger the amount of oxygen supplied to the filter 33 and the second catalyst 32b. Specifically, when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD1, the amount of oxygen supplied to the filter 33 and the second catalyst 32b is minimum. The amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD2 is greater than the amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD1. The amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD0 is greater than the amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD2. The amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD3 is greater than the amount of oxygen supplied when the lean-determined air-fuel ratio LD is set to the air-fuel ratio LD0. The amount of oxygen supplied when the lean judged air-fuel ratio LD is set to the air-fuel ratio LD4 is greater than the amount of oxygen supplied when the lean judged air-fuel ratio LD is set to the air-fuel ratio LD3.

[0025] The ECU 100 sets the lean judgment air-fuel ratio LD to one of the air-fuel ratios LD0 to LD4 by referring to the map of FIG. 3. FIG. 3 is an example of a map that defines the lean judgment air-fuel ratio LD that is set according to the accumulation amount P of exhaust particulates accumulated in the filter 33 and the temperature T of the filter 33. FIG. 3 shows accumulation amount thresholds P0 to P2 and temperature thresholds T0 to T2. Of the accumulation amount thresholds P0 to P2, the accumulation amount threshold P0 is the smallest. The accumulation amount threshold P1 is higher than the accumulation amount threshold P2. The accumulation amount threshold P0 is an example of a reference accumulation amount threshold. The accumulation amount thresholds P1 and P2 are examples of first and second accumulation amount thresholds, respectively. Of the temperature thresholds T0 to T2, the temperature threshold T0 is the lowest temperature. The temperature threshold T1 is higher than the temperature threshold T2. The temperature threshold T0 is an example of a reference temperature threshold. The temperature thresholds T1 and T2 are examples of first and second temperature thresholds, respectively. The ECU 100 sets the lean judged air-fuel ratio LD to one of the air-fuel ratios LD0 to LD4 in accordance with the temperature T and the accumulation amount P.

[0026] FIG. 4 is a flowchart illustrating air-fuel ratio control. This air-fuel ratio control is repeatedly executed while the engine system 1 is operating. The ECU 100 acquires the amount P of exhaust particulate matter accumulated on the filter 33, the temperature T of the filter 33, and the intake air amount Ga (step S1). The accumulation amount P is estimated based on the pressure difference before and after the filter 33. The temperature T is estimated based on the engine speed, the engine load factor, and the ignition timing. The accumulation amount P may also be estimated based on the temperature of the engine coolant or the operating history. The temperature T may be detected by a temperature sensor provided on the filter 33. The temperature T and the accumulation amount P may also be estimated by other known methods. The intake air amount Ga is detected by the air flow meter 22. Step S1 is an example of processing executed by the acquisition unit.

[0027] The ECU 100 determines whether the temperature T is higher than the temperature threshold T1 and whether the accumulation amount P is greater than the accumulation amount threshold P1 (step S2). If the answer to step S2 is Yes, and the amount of oxygen supplied to the filter 33 is large, the exhaust particulates accumulated in large amounts on the filter 33 may be burned, causing the temperature of the filter 33 to rise excessively. Therefore, if the answer to step S2 is Yes, the ECU 100 sets the lean determination air-fuel ratio LD to the air-fuel ratio LD1 (step S3). This reduces the amount of oxygen supplied to the filter 33, thereby preventing the temperature of the filter 33 from rising excessively. If the answer to step S2 is Yes, this is an example of the first state.

[0028] If the answer is No in step S2, the ECU 100 determines whether the temperature T is higher than the temperature threshold T2 and whether the deposition amount P is greater than the deposition amount threshold P2 (step S4). If the answer is Yes in step S4 and the amount of oxygen supplied to the filter 33 is large, both the filter 33 and the second catalyst 32b may become hot and may be thermally deteriorated. Therefore, if the answer is Yes in step S4, the ECU 100 sets the lean determination air-fuel ratio LD to the air-fuel ratio LD2 (step S5). This reduces the amount of oxygen supplied to the filter 33 and the second catalyst 32b, thereby suppressing thermal deterioration of the filter 33 and the second catalyst 32b. If the answer is No in step S2 and Yes in step S4, this is an example of the second state.

[0029] If the answer is No in step S4, the ECU 100 determines whether the temperature T is greater than the temperature threshold T0 and the deposition amount P is greater than the deposition amount threshold P0 (step S6). If the answer is Yes in step S6, the ECU 100 determines whether the intake air amount Ga is greater than a predetermined value (step S7). If the answers are Yes in steps S6 and S7, the flow rate of the exhaust gas passing through the second catalyst 32b is high, which may result in a decrease in the purification reaction in the second catalyst 32b. Therefore, if the answers are Yes in steps S6 and S7, the ECU 100 sets the lean judgment air-fuel ratio LD to the air-fuel ratio LD3 (step S8). This ensures the amount of oxygen supplied to the second catalyst 32b and suppresses a decrease in the purification ability of the second catalyst 32b.

[0030] If the answer is Yes in step S6 and No in step S7, the flow rate of exhaust gas passing through the filter 33 is slow, the amount of oxygen supplied to the filter 33 is insufficient, and the exhaust particulates deposited on the filter 33 are difficult to burn. Therefore, if the answer is Yes in step S6 and No in step S7, the ECU 100 sets the lean judgment air-fuel ratio LD to the air-fuel ratio LD4 (step S9). This ensures the amount of oxygen supplied to the filter 33, and promotes the combustion of the exhaust particulates. If the answer is No in step S6, the ECU 100 sets the lean judgment air-fuel ratio LD to the air-fuel ratio LD0 (step S10). If the answer is No in steps S2 and S4 and Yes in step S6, this is an example of the third state. If the answer is No in steps S2, S4, and S6, this is an example of the reference state. Steps S3, S5, S8, S9, and S10 are examples of processing executed by the oxygen supply amount control unit.

[0031] As described above, the amount of oxygen supplied to the filter 33 and the second catalyst 32b can be controlled by setting the lean judged air-fuel ratio LD in accordance with the temperature T of the filter 33 and the deposition amount P. This makes it possible to suppress the occurrence of various problems depending on the state of the filter 33.

[0032] [Variations] Next, a modified example of air-fuel ratio control will be described. In this modified example, the lean target air-fuel ratio TL is set to one of the air-fuel ratios TL0 to TL4. FIG. 5 is a timing chart illustrating an example of the transition of the target air-fuel ratio TAF. Of the air-fuel ratios TL0 to TL4, the air-fuel ratio TL1 is the smallest. The air-fuel ratio TL2 is greater than the air-fuel ratio TL1. The air-fuel ratio TL0 is greater than the air-fuel ratio TL2. The air-fuel ratio TL3 is greater than the air-fuel ratio TL0. The air-fuel ratio TL4 is greater than the air-fuel ratio TL3. First, the transition of the target air-fuel ratio TAF when the lean target air-fuel ratio TL is set to the air-fuel ratio TL0 will be described. When the lean target air-fuel ratio TL is set to the air-fuel ratio TL0 and the detected air-fuel ratio AFb rises to the lean determined air-fuel ratio LD, the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR (time t1). Thereafter, when the detected air-fuel ratio AFb drops to the rich judged air-fuel ratio RD, the target air-fuel ratio TAF is switched from the predetermined rich target air-fuel ratio TR to the lean target air-fuel ratio TL (time t2).

[0033] FIG. 5 shows target air-fuel ratios TAF1 to TAF4 when the lean target air-fuel ratio TL is set to each of the air-fuel ratios TL1 to TL4. The larger the set lean target air-fuel ratio TL, the higher the oxygen concentration of the exhaust gas supplied to the first catalyst 32a. Therefore, the larger the set lean target air-fuel ratio TL, the earlier the oxygen storage amount of the first catalyst 32a increases, and the earlier the detected air-fuel ratio AFb reaches the lean determined air-fuel ratio LD. Here, the filter 33 is provided at a position away from the exhaust port of the engine body 10. Therefore, the exhaust gas discharged from the exhaust port of the engine body 10 reaches the filter 33 after a predetermined time has elapsed. Therefore, it takes time for the rich exhaust gas generated when the target air-fuel ratio TAF is switched from the lean target air-fuel ratio TL to the rich target air-fuel ratio TR to reach the filter 33 from the engine body 10. Before this rich exhaust gas reaches the filter 33, lean exhaust gas generated when the target air-fuel ratio TAF was set to the lean target air-fuel ratio TL is supplied to the filter 33. The higher the oxygen concentration of this lean exhaust gas, the greater the amount of oxygen supplied to the filter 33 and the second catalyst 32b. That is, the greater the lean target air-fuel ratio TL, the greater the amount of oxygen supplied to the filter 33 and the second catalyst 32b.

[0034] Therefore, when the lean target air-fuel ratio TL is set to the air-fuel ratio TL1, the amount of oxygen supplied to the filter 33 and the second catalyst 32b is minimum. The amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL2 is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL1. The amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL0 is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL2. The amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL3 is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL0. The amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL4 is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL3.

[0035] The ECU 100 sets the lean target air-fuel ratio TL to one of the air-fuel ratios TL0 to TL4 by referring to the map of Fig. 6. Fig. 6 is an example of a map that defines the lean target air-fuel ratio TL that is set in accordance with the accumulation amount P of exhaust particulates accumulated on the filter 33 and the temperature T of the filter 33. Fig. 6 corresponds to Fig. 3.

[0036] FIG. 7 is a flowchart illustrating an example of air-fuel ratio control according to a modified example. FIG. 7 corresponds to FIG. 4. The same steps as those in FIG. 4 will not be described again. If the answer to step S2 is Yes, the ECU 100 sets the lean target air-fuel ratio TL to the air-fuel ratio TL1 (step S3a). This reduces the amount of oxygen supplied to the filter 33, thereby preventing the filter 33 from overheating. If the answer to step S4 is Yes, the ECU 100 sets the lean target air-fuel ratio TL to the air-fuel ratio TL2 (step S5a). This reduces the amount of oxygen supplied to the filter 33 and the second catalyst 32b, thereby preventing thermal deterioration of the filter 33 and the second catalyst 32b. If the answers to steps S6 and S7 are Yes, the ECU 100 sets the lean target air-fuel ratio TL to the air-fuel ratio TL3 (step S8a). This ensures the amount of oxygen supplied to the second catalyst 32b, thereby preventing a decrease in the purification capacity of the second catalyst 32b. If the answer is Yes in step S6 and No in step S7, the ECU 100 sets the lean target air-fuel ratio TL to the air-fuel ratio TL4 (step S9a). This ensures the supply of oxygen to the filter 33, thereby promoting the combustion of exhaust particulates. If the answer is No in step S6, the ECU 100 sets the lean target air-fuel ratio TL to the air-fuel ratio TL0 (step S10a).

[0037] As described above, the amount of oxygen supplied to the filter 33 and the second catalyst 32b can be controlled by setting the lean target air-fuel ratio TL in accordance with the temperature T and the deposition amount P of the filter 33. This makes it possible to suppress the occurrence of various problems depending on the state of the filter 33.

[0038] The above-described embodiment and this modification may be combined. That is, the amount of oxygen supplied to the filter 33 and the second catalyst 32b may be controlled by setting both the lean judged air-fuel ratio LD and the lean target air-fuel ratio TL in accordance with the temperature T and the accumulation amount P of the filter 33.

[0039] 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]

[0040] 1 Engine System 10 Engine body 30 Exhaust passage 31b Second sensor (sensor) 32a 1st catalyst 32b 2nd catalyst 33 Filters 100 ECU (air-fuel ratio control unit, acquisition unit, oxygen supply amount control unit)

Claims

1. The engine body and an exhaust passage connected to the engine body; a first catalyst disposed in the exhaust passage and having an oxygen storage capacity; a second catalyst disposed downstream of the first catalyst in the exhaust passage; a filter disposed in the exhaust passage between the first catalyst and the second catalyst; a sensor disposed in the exhaust passage between the first catalyst and the filter, the sensor detecting an air-fuel ratio of the exhaust gas; a control device that controls an air-fuel ratio of the engine body to a target air-fuel ratio by controlling a fuel injection amount and an intake air amount of the engine body, The control device an air-fuel ratio control unit that switches the target air-fuel ratio from a target lean air-fuel ratio higher than the stoichiometric air-fuel ratio to a target rich air-fuel ratio lower than the stoichiometric air-fuel ratio when the detected air-fuel ratio detected by the sensor becomes equal to or higher than a lean judged air-fuel ratio higher than the stoichiometric air-fuel ratio, and switches the target air-fuel ratio from the target rich air-fuel ratio to the target lean air-fuel ratio when the detected air-fuel ratio becomes a rich judged air-fuel ratio lower than the stoichiometric air-fuel ratio; an acquisition unit that acquires the temperature of the filter and the amount of exhaust particulate matter deposited on the filter; an oxygen supply amount control unit that controls the amount of oxygen supplied to the filter and the second catalyst by setting at least one of the lean judged air-fuel ratio and the target lean air-fuel ratio in accordance with the temperature and the amount of deposition.

2. In a first state in which the temperature is higher than a first temperature threshold and the deposition amount is larger than a first deposition amount threshold, the oxygen supply amount control unit reduces the oxygen supply amount by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio, compared to a reference state in which the temperature is equal to or lower than a reference temperature threshold and the deposition amount is equal to or lower than a reference deposition amount threshold, the first temperature threshold is higher than the reference temperature threshold; The engine system of claim 1 , wherein the first accumulation threshold is greater than the reference accumulation threshold.

3. In a second state in which the temperature is higher than a second temperature threshold and equal to or lower than the first temperature threshold, and the accumulation amount is greater than a second accumulation amount threshold and equal to or lower than the first accumulation amount threshold, the oxygen supply amount control unit increases the oxygen supply amount compared to the first state and decreases the oxygen supply amount compared to the reference state by setting at least one of the lean judgment air-fuel ratio and a target lean air-fuel ratio, the second temperature threshold is lower than the first temperature threshold and higher than the reference temperature threshold; The engine system of claim 2 , wherein the second accumulation amount threshold is smaller than the first accumulation amount threshold and larger than the reference accumulation amount threshold.

4. 4. The engine system of claim 3, wherein in a third state in which the temperature is higher than the reference temperature threshold but not higher than the second temperature threshold and the deposition amount is greater than the reference deposition amount threshold but not higher than the second deposition amount threshold, the oxygen supply amount control unit increases the oxygen supply amount compared to the reference state by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio.

5. The acquisition unit acquires an intake air amount of the engine body, 5. The engine system of claim 4, wherein when the intake air amount of the engine in the third state is greater than an air amount threshold, the oxygen supply amount control unit reduces the oxygen supply amount by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio, compared to when the intake air amount is equal to or less than the air amount threshold in the third state.

Images