JP7740274B2 - Engine System - Google Patents

Description

The present invention relates to an engine system.

In some cases, a filter is provided between a first catalyst and a second catalyst, which are located upstream and downstream of the exhaust passage connected to the engine body (see Patent Document 1).

JP 2009-127559 A

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.

The objective is to provide an engine system that can control the amount of oxygen supplied to the filter and second catalyst depending on the condition of the filter.

The above object is to provide an engine comprising an engine body, an exhaust passage connected to the engine body, a first catalyst disposed in the exhaust passage and having oxygen storage capacity, a second catalyst disposed in the exhaust passage downstream of the first catalyst, 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 and detecting the air-fuel ratio of the exhaust gas, and a control device that controls the air-fuel ratio of the engine body to a target air-fuel ratio by controlling the amount of fuel injection and the amount of intake air 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 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 becomes equal to or higher than a lean judgment air-fuel ratio higher 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; and an oxygen supply amount control unit that controls the amount of oxygen supplied to the filter and second catalyst by setting at least one of the lean judgment air-fuel ratio and the target lean air-fuel ratio according to the temperature and the amount of deposition.

In a first state in which the temperature is higher than the first temperature threshold and the deposition amount is greater than the 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 the reference temperature threshold and the deposition amount is equal to or lower than the 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 greater than the reference deposition amount threshold.

In a second state in which the temperature is higher than the second temperature threshold but equal to or lower than the first temperature threshold, and the deposition amount is greater than the second deposition amount threshold but 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.

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.

The acquisition unit may acquire the 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.

It is possible to provide an engine system that can control the amount of oxygen supplied to the filter and second catalyst depending on the condition of the filter.

FIG. 1 is a schematic configuration diagram of an engine system. 10 is a timing chart illustrating the transition of the detected air-fuel ratio AFb. 10 is a diagram illustrating 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. 3 is a flowchart illustrating an example of air-fuel ratio control. 4 is a timing chart illustrating the transition of the target air-fuel ratio TAF. 10 is a diagram illustrating 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. 10 is a flowchart illustrating a modified example of air-fuel ratio control.

[General configuration of engine system]
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. The intake valve 18a opens and closes the intake port of the engine body 10. The exhaust valve 18b opens and closes the exhaust port of the engine body 10.

In the intake passage 20, an air cleaner 21, an air flow meter 22, and a throttle valve 23 are provided, 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 volume Ga. The throttle valve 23 adjusts the intake air volume Ga.

When the intake valve 18a opens, air is introduced from the intake passage 20 into the combustion chamber 11. The mixture of fuel and air 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, rotating the crankshaft 14. Exhaust gases after combustion are discharged through the exhaust passage 30.

The exhaust passage 30 is provided with, from upstream to downstream, a first sensor 31a, a first catalyst 32a, a second sensor 31b, a filter 33, and a second catalyst 32b. The first sensor 31a and the second sensor 31b are air-fuel ratio sensors that detect the air-fuel ratio of the 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 the exhaust gas by detecting the oxygen concentration of the exhaust gas. The first sensor 31a detects the air-fuel ratio of the 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 the 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.

The first catalyst 32a and second catalyst 32b are three-way catalysts containing the catalytic metals platinum (Pt), palladium (Pd), and rhodium (Rh) and possessing oxygen storage capacity. By possessing catalytic activity and oxygen storage capacity, three-way catalysts purify NOx and HC according to the amount of oxygen stored. Note that the second catalyst 32b does not necessarily have oxygen storage capacity.

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 storage device. The ECU 100 controls the spark plugs 16, in-cylinder injection valves 17, and throttle valve 23 based on the amount of operation of the accelerator pedal and brake pedal operated by the driver, as well as the engine speed and load of the engine body 10. The ECU 100 receives detection values from the engine speed sensor 15, air flow meter 22, first sensor 31a, and second sensor 31b. The ECU 100 also functionally implements the air-fuel ratio control unit, acquisition unit, and oxygen supply amount control unit, described below, using the CPU, RAM, ROM, and storage device.

[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 air-fuel ratio AFa detected by 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.

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 greater than the stoichiometric air-fuel ratio ST. Here, the lean judged air-fuel ratio LD is greater than the stoichiometric air-fuel ratio ST. The rich judged air-fuel ratio RD is less than the stoichiometric air-fuel ratio ST. The lean target air-fuel ratio TL is greater than the stoichiometric air-fuel ratio ST. The rich target air-fuel ratio TR is less 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 performed by the air-fuel ratio control unit.

Figure 2 is a timing chart illustrating the progression of the detected air-fuel ratio AFb. In this embodiment, the lean judgment 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 the air-fuel ratio LD0. The air-fuel ratio LD4 is greater than the air-fuel ratio LD3. First, we will explain the progression of the detected air-fuel ratio AFb when the lean judgment air-fuel ratio LD is set to the air-fuel ratio LD0. 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, the 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. As the amount of oxygen stored in 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.

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 the predetermined rich target air-fuel ratio TR to the 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. As the amount of oxygen stored in the first catalyst 32a increases, the oxygen concentration in the exhaust gas discharged from the first catalyst 32a increases, and the detected air-fuel ratio AFb rises toward the lean side.

Figure 2 shows detected air-fuel ratios AFb1 to AFb4 when the lean judgment 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.

The larger the lean-determined air-fuel ratio LD that is set, 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 lean-determined air-fuel ratio LD that is set, the greater 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 judged air-fuel ratio LD is set to the air-fuel ratio LD3 is greater than the amount of oxygen supplied when the lean judged 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.

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 in FIG. 3. FIG. 3 is an example of a map that defines the lean judgment air-fuel ratio LD, which 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, accumulation amount threshold P0 is the smallest. Accumulation amount threshold P1 is higher than accumulation amount threshold P2. Accumulation amount threshold P0 is an example of a reference accumulation amount threshold. Accumulation amount thresholds P1 and P2 are examples of first and second accumulation amount thresholds, respectively. Of the temperature thresholds T0 to T2, temperature threshold T0 is the lowest temperature. Temperature threshold T1 is higher than temperature threshold T2. Temperature threshold T0 is an example of a reference temperature threshold. Temperature thresholds T1 and T2 are examples of first and second temperature thresholds, respectively. The ECU 100 sets the lean judgment air-fuel ratio LD to one of the air-fuel ratios LD0 to LD4 depending on the temperature T and the accumulation amount P.

Figure 4 is a flowchart illustrating air-fuel ratio control. This air-fuel ratio control is repeatedly performed 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, engine load factor, and ignition timing. The accumulation amount P may also be estimated based on the temperature of the engine coolant or operating history. The temperature T may be detected by a temperature sensor provided on the filter 33. The temperature T and 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 performed by the acquisition unit.

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 burn, causing the filter 33 to overheat. 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 filter 33 from overheating. If the answer to step S2 is Yes, this is an example of the first state.

If step S2 is No, ECU 100 determines whether temperature T is higher than temperature threshold T2 and whether deposition amount P is greater than deposition amount threshold P2 (step S4). If step S4 is Yes 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 suffer thermal degradation. Therefore, if step S4 is Yes, 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 preventing thermal degradation of the filter 33 and the second catalyst 32b. If step S2 is No and step S4 is Yes, this is an example of the second state.

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 both 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 both 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 capacity of the second catalyst 32b.

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

As described above, by setting the lean judgment air-fuel ratio LD according to the temperature T and deposition amount P of the filter 33, it is possible to control the amount of oxygen supplied to the filter 33 and second catalyst 32b. This makes it possible to prevent various problems caused by the condition of the filter 33.

[Modification]
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, a description will be given of 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. 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 judged 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). After that, when the detected air-fuel ratio AFb falls 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).

Figure 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 higher 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 higher 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 judgment air-fuel ratio LD. Here, the filter 33 is located away from the exhaust port of the engine body 10. Therefore, exhaust gas discharged from the exhaust port of the engine body 10 reaches the filter 33 after a predetermined time has elapsed. Therefore, 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 takes time 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 is 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. In other words, 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.

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. When the lean target air-fuel ratio TL is set to the air-fuel ratio TL2, the amount of oxygen supplied is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL1. When the lean target air-fuel ratio TL is set to the air-fuel ratio TL0, the amount of oxygen supplied is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL2. When the lean target air-fuel ratio TL is set to the air-fuel ratio TL3, the amount of oxygen supplied is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL0. When the lean target air-fuel ratio TL is set to the air-fuel ratio TL4, the amount of oxygen supplied is greater than the amount of oxygen supplied when the lean target air-fuel ratio TL is set to the air-fuel ratio TL3.

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 in Figure 6. Figure 6 is an example of a map that defines the lean target air-fuel ratio TL, which is set according to the amount P of exhaust particulate matter accumulated on the filter 33 and the temperature T of the filter 33. Figure 6 corresponds to Figure 3.

Figure 7 is a flowchart illustrating a modified example of air-fuel ratio control. Figure 7 corresponds to Figure 4. Explanations of steps in Figure 7 that are the same as those in Figure 4 will be omitted. If the answer is Yes in step S2, 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 is Yes in step S4, 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 are Yes in steps S6 and S7, 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 step S6 is Yes and step S7 is No, ECU 100 sets the lean target air-fuel ratio TL to air-fuel ratio TL4 (step S9a). This ensures the supply of oxygen to filter 33 and promotes the combustion of exhaust particulates. If step S6 is No, ECU 100 sets the lean target air-fuel ratio TL to air-fuel ratio TL0 (step S10a).

As described above, by setting the lean target air-fuel ratio TL according to the temperature T and deposition amount P of the filter 33, it is possible to control the amount of oxygen supplied to the filter 33 and second catalyst 32b. This makes it possible to prevent various problems caused by the condition of the filter 33.

The above-described embodiment may be combined with this modified example. That is, the amount of oxygen supplied to the filter 33 and the second catalyst 32b may be controlled by setting both the lean judgment air-fuel ratio LD and the lean target air-fuel ratio TL according to the temperature T and deposition amount P of the filter 33.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims.

1 Engine system 10 Engine body 30 Exhaust passage 31b Second sensor (sensor)
32a First catalyst 32b Second catalyst 33 Filter 100 ECU (air-fuel ratio control unit, acquisition unit, oxygen supply amount control unit)

Claims (5)

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. 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. 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. The engine system of claim 3, wherein in a third state in which the temperature is higher than the reference temperature threshold but equal to or lower than the second temperature threshold and the deposition amount is higher than the reference deposition amount threshold but equal to or lower 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. 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.