JP2022053872A - Engine system - Google Patents

Abstract

To suppress deterioration of exhaust emission control performance of an exhaust gas treatment device while inhibiting an operating state of a supercharger from entering a surge region.SOLUTION: An ECU executes processing including: a step (S102) of calculating an operating region of a supercharger; a step (S106) of opening a second throttle valve when the operating region of the supercharger is within a predetermined range (Yes in S104); a step (S108) of acquiring first pressure and second pressure; a step (S110) of calculating a flow rate of a bypass passage; a step (S112) of controlling an engine to a target air-fuel ratio; and a step (S116) of closing the second throttle valve if the second throttle valve is in a valve opening state (Yes in S114) when the operating region of the supercharger is not within the predetermined range (No in S104).SELECTED DRAWING: Figure 2

Description

The present invention relates to the control of an engine system including a turbocharger and an exhaust treatment device.

In an engine equipped with a turbocharger, it is known to provide a bypass passage connecting the passage downstream of the compressor of the turbocharger and the passage downstream of the turbine so that the operating state of the turbocharger does not enter the surge region. be.

For example, in Japanese Patent Application Laid-Open No. 2007-162545 (Patent Document 1), a bypass flow path is provided between the downstream side of the compressor and the turbine and the catalyst, and gas in the bypass flow path is allowed to flow when a surge enters. Avoiding surges is disclosed.

JP-A-2007-162545

However, if the gas downstream of the compressor is circulated downstream of the turbine via the bypass passage so that the operating state of the turbocharger does not enter the surge region, the purification performance of the exhaust treatment device that purifies the exhaust gas downstream of the turbine is sufficient. It may not be possible to demonstrate it. This is because the temperature of the exhaust gas treatment device is lowered by the gas supplied downstream of the turbine via the bypass passage, and the temperature of the exhaust gas treatment device is out of the temperature range in which the purification performance of the exhaust gas treatment device is fully functional.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to prevent the operating state of the turbocharger from entering the surge region and to reduce the exhaust gas purification performance of the exhaust gas treatment device. It is to provide an engine system that suppresses.

An engine system according to an aspect of the present invention includes an engine, a turbocharger provided in an intake passage of the engine, a supercharger for supercharging the intake air sucked into the engine by using the compressor, and an exhaust passage of the engine. A plurality of exhaust treatment devices that purify the exhaust discharged from the engine, a first throttle valve that is installed between the compressor and the engine and is configured to be able to adjust the amount of air flowing through the intake passage, and an intake passage. A bypass passage in which one end is connected to a position between the compressor and the first throttle valve in the exhaust passage and the other end is connected to a position between two of the plurality of exhaust treatment devices in the exhaust passage. It includes a second throttle valve configured to be able to adjust the amount of air flowing through the bypass passage, and a control device for controlling the operation of the second throttle valve. The control device controls the second throttle valve so that the valve is opened in the state of being supercharged by the supercharger when a predetermined condition is satisfied.

In this way, when a predetermined condition is satisfied, the second throttle valve is opened in the state of being supercharged by the supercharger, so that the gas flowing between the compressor and the engine is opened. A part of the gas can be distributed downstream of the turbine via the bypass passage. Therefore, the pressure of the gas between the compressor and the engine can be adjusted to an appropriate pressure. Therefore, it is possible to prevent the operating region of the compressor from becoming a surge region. Further, air is supplied to the downstream side of the position where the other end of the bypass passage of the plurality of exhaust treatment devices is connected, and the air-fuel ratio of the exhaust supplied to the exhaust gas treatment device on the downstream side is set to a lean state. Can be done. Since the air-fuel ratio of the exhaust gas can be changed between the upstream side and the downstream side in this way, by supplying the exhaust gas with an appropriate air-fuel ratio between the upstream side and the downstream side to the exhaust gas treatment device, each exhaust gas treatment device. It is possible to improve the purification performance of the exhaust gas in.

Further, in a certain embodiment, a predetermined condition is that the operating region of the turbocharger, which is indicated by the pressure ratio in the compressor and the intake air amount, is on the surge region of the turbocharger and the intake air amount side of the surge region. It includes the condition that it is within the range including the first region adjacent to the boundary.

In this way, when a predetermined condition is satisfied, the second throttle valve is opened in the state of being supercharged by the supercharger, so that the gas flowing between the compressor and the engine is opened. A part of the gas can be distributed downstream of the turbine via the bypass passage. Therefore, it is possible to prevent the operating region of the turbocharger from changing to the surge region.

Further, in one embodiment, the control device has a working region represented by a pressure ratio calculated using a first pressure of air flowing out of the compressor and atmospheric pressure, and an amount of intake air flowing into the compressor. The operation with the second throttle valve is controlled so as to be within a predetermined second region including one region.

In this way, when a predetermined condition is satisfied, the second throttle valve is opened in the state of being supercharged by the supercharger, so that the gas flowing between the compressor and the engine is opened. A part of the gas can be distributed downstream of the turbine via the bypass passage. Therefore, it is possible to suppress the change of the operating region of the compressor to the surge region and appropriately operate the turbocharger within the range of the second region.

Further, in one embodiment, the upstream exhaust treatment device on the upstream side of the flowing exhaust gas among the two exhaust gas treatment devices includes a three-way catalyst, an oxidation catalyst, a PM removal filter, and a NOx purification catalyst. Includes at least one of.

In this way, the exhaust gas treatment device on the upstream side including at least one of the three-way catalyst, the oxidation catalyst, the PM removal filter, and the NOx purification catalyst is supplied with air via the bypass passage. Excluded. Therefore, it is possible to suppress the change of the air-fuel ratio of the exhaust gas flowing through the exhaust gas treatment device on the upstream side to the lean side and to prevent the temperature from dropping unnecessarily. As a result, it is possible to suppress the deterioration of the exhaust gas purification performance in the exhaust gas treatment device on the upstream side due to the change in the air-fuel ratio and the temperature decrease.

Further, in one embodiment, the upstream exhaust treatment device on the upstream side of the circulating exhaust of the two exhaust treatment devices includes a three-way catalyst. The downstream exhaust gas treatment device on the downstream side of the flowing exhaust gas among the two exhaust gas treatment devices includes at least one of a three-way catalyst, an oxidation catalyst, and a NOx purification catalyst. The predetermined conditions are that the oxygen storage amount in the upstream exhaust treatment device is lower than the threshold value and that the air-fuel ratio of the engine exhaust is at least one of a stoichiometric state and a rich state. Includes the condition that

By doing so, even if the predetermined conditions are satisfied and the second throttle valve is opened, the exhaust gas of the engine having the air-fuel ratio in the stoichiometric state or the rich state is included in the upstream exhaust treatment device. Since it is supplied to the original catalyst, NOx can be appropriately purified. Further, since air is supplied to the downstream exhaust treatment device via the bypass passage, the air-fuel ratio of the exhaust supplied to at least one of the three-way catalyst, the oxidation catalyst, and the NOx purification catalyst is set to the lean side. Can be changed to a value. Therefore, it is possible to improve the exhaust gas purification performance in these downstream exhaust gas treatment devices.

Further, in one embodiment, the upstream exhaust treatment device on the upstream side of the circulating exhaust of the two exhaust treatment devices includes a three-way catalyst. The downstream exhaust gas treatment device on the downstream side of the circulating exhaust gas among the two exhaust gas treatment devices includes a PM removal filter and a NOx purification catalyst.

By doing so, even if the predetermined conditions are satisfied and the second throttle valve is opened, the exhaust gas of the engine having the air-fuel ratio in the stoichiometric state and the rich state is included in the upstream exhaust treatment device. Since it is supplied to the original catalyst, NOx can be appropriately purified. Further, since the air is supplied to the downstream exhaust gas treatment device via the bypass passage, the air-fuel ratio of the exhaust gas flowing to the downstream exhaust gas treatment device can be changed to the lean side value. Therefore, the NOx can be purified by using the NOx purification catalyst, and the soot collected by the PM removal filter can be burned to regenerate the PM removal filter.

Further in certain embodiments, the NOx purification catalyst comprises at least one of a selective reduction NOx purification catalyst and a storage reduction NOx purification catalyst.

By doing so, when a selective reduction type NOx catalyst, an occlusion reduction NOx catalyst, or the like is used as the NOx purification catalyst, NOx can be appropriately purified.

Further, in one embodiment, the downstream exhaust treatment device on the downstream side of the circulating exhaust of the two exhaust treatment devices includes a PM removal filter. The predetermined conditions include the condition that the amount of PM deposited in the PM removal filter is larger than the threshold value.

In this way, when the predetermined execution conditions are satisfied and the second throttle valve is opened, the air supplied via the bypass passage causes the PM removal filter included in the downstream exhaust treatment device to be used. The air-fuel ratio of the circulated exhaust gas can be changed to the lean side. Therefore, the soot deposited on the PM removal filter can be burned to regenerate the PM removal filter.

Further, in certain embodiments, the turbocharger includes an adjusting device capable of adjusting the supercharging pressure. When a predetermined condition is satisfied, the control device controls the adjusting device so that the boost pressure becomes higher than the threshold value, and opens the second throttle valve.

By doing so, by opening the second throttle valve while being supercharged by the turbocharger, the air is discharged via the bypass passage to the downstream side of the two exhaust treatment devices. Can be supplied to the device. Therefore, it is possible to suppress the deterioration of the exhaust gas purification performance in the exhaust gas treatment device.

Further, in one embodiment, the control device calculates the flow rate of the gas flowing through the bypass passage and calculates the flow rate of the gas flowing through the engine calculated using the calculated flow rate.

By doing so, when the second throttle valve is opened, the flow rate of the gas flowing through the engine can be calculated. Therefore, the fuel injection amount of the engine is appropriately adjusted and the air-fuel ratio of the exhaust is appropriately adjusted. It can be adjusted to a high air-fuel ratio.

Further, in one embodiment, the control device calculates the flow rate of the gas flowing through the bypass passage and adjusts the opening degree of the second throttle valve so that the calculated flow rate becomes the target flow rate.

By doing so, when the second throttle valve is opened, the flow rate of the gas flowing through the bypass passage can be adjusted to the target flow rate, so that the exhaust treatment on the downstream side of the two exhaust treatment devices can be performed. The amount of air supplied to the device can be adjusted to an appropriate amount. Therefore, it is possible to suppress deterioration of the exhaust purification performance of the exhaust gas treatment device on the downstream side.

In a further embodiment, the engine system comprises a first pressure detector that detects the first pressure of the gas flowing between the compressor and the first throttle valve in the intake passage and a second of the gas in the bypass passage. Further, a second pressure detecting device for detecting the pressure is provided. The control device calculates the flow rate of the gas flowing through the bypass passage using the difference between the first pressure and the second pressure.

By doing so, the flow rate of the gas flowing through the bypass passage can be calculated with high accuracy by using the difference between the first pressure and the second pressure.

In a further embodiment, the engine system is further provided with a valve provided in the bypass passage to prevent backflow of gas from one end to the other in the bypass passage.

By doing so, it is possible to suppress the backflow of gas from the exhaust side to the intake side via the bypass passage.

According to the present invention, it is possible to provide an engine system that suppresses the deterioration of the exhaust gas purification performance of the exhaust gas treatment device while suppressing the operating state of the turbocharger from entering the surge region.

It is a figure which shows an example of the schematic structure of the engine system in 1st Embodiment. It is a flowchart which shows an example of the process executed by the ECU in 1st Embodiment. It is a figure which shows an example of the predetermined range of the operating point of a supercharger. It is a figure for demonstrating the change of the operating point of a supercharger by the operation of an ECU. It is a figure which shows an example of the schematic structure of the engine system which concerns on the modification of 1st Embodiment. It is a figure for demonstrating an example of the temperature change of DOC in the modification of 1st Embodiment. It is a figure which shows an example of the schematic structure of the engine system which concerns on 2nd Embodiment. It is a flowchart which shows an example of the process executed by the ECU in the 2nd Embodiment. It is a timing chart which shows the change of the air-fuel ratio, the oxygen occlusion amount, and the NOx emission amount. It is a figure which shows an example of the schematic structure of the engine system which concerns on 3rd Embodiment. It is a flowchart which shows an example of the process executed by the ECU in the 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, detailed explanations about them will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing an example of a schematic configuration of an engine system 1 according to a first embodiment. The engine system 1 includes an engine 2, a first throttle valve 12, a supercharger 50, a three-way catalyst (hereinafter, also referred to as TWC (Three-Way Catalyst)) 60, a PM removal filter 62, and NOx. It includes a purification catalyst 64, a bypass passage 70, a second throttle valve 72, an EGR (Exhaust Gas Recirculation) passage 80, an EGR valve 82, and an ECU (Electronic Control Unit) 100. The engine system 1 is mounted as a power source on a moving body such as a vehicle.

In the present embodiment, the engine 2 will be described, for example, by taking a diesel engine as an example, but may be another internal combustion engine such as a gasoline engine. The engine 2 includes, for example, a plurality of cylinders and a fuel injection device (none of which is shown) for injecting fuel into the cylinders. The amount of fuel supplied to the engine 2 is controlled, for example, by the engine control unit 102 of the ECU 100.

The turbocharger 50 includes a compressor 52, a turbine 54, and a shaft 56. One end of the first intake passage 10 is connected to the intake inlet of the compressor 52. An air cleaner (not shown) is provided at the other end of the first intake passage 10. A flow meter 200 is provided in the middle of the first intake passage 10.

The flow meter 200 detects the flow rate of the air flowing through the first intake passage 10 (hereinafter, referred to as the intake air amount). The flow meter 200 transmits a signal indicating the detected intake air amount to the ECU 100.

One end of the second intake passage 20 is connected to the intake outlet of the compressor 52. The other end of the second intake passage 20 is connected to an intake manifold (not shown) of the engine 2. Further, although not particularly shown, an intercooler (not shown) is provided in the middle of the second intake passage 20. A compressor wheel (not shown) is rotatably provided in the compressor 52.

The other end of the first exhaust passage 30 whose one end is connected to the exhaust manifold (not shown) of the engine 2 is connected to the exhaust inlet of the turbine 54. One end of the second exhaust passage 40 is connected to the exhaust outlet of the turbine 54. A turbine wheel (not shown) is rotatably provided in the turbine 54.

The shaft 56 connects a compressor wheel (not shown) in the compressor 52 and a turbine wheel (not shown) in the turbine 54.

The turbine wheel in the turbine 54 is rotated by the exhaust gas flowing from the exhaust inlet through the first exhaust passage 30 from the engine 2. The rotational force of the turbine wheel is transmitted to the compressor wheel in the compressor 52 via the shaft 56. As the compressor wheel rotates due to the transmitted rotational force, the air flowing from the first intake passage 10 is compressed and supplied from the intake outlet to the second intake passage 20.

A first pressure gauge 202 is provided in the second intake passage 20. The first pressure gauge 202 detects the pressure of the gas flowing out from the compressor 52 (hereinafter referred to as the first pressure). The first pressure gauge 202 transmits a signal indicating the detected first pressure to the ECU 100.

One end of the bypass passage 70 is connected to the second intake passage 20 on the downstream side of the compressor 52. Further, a first throttle valve 12 is provided at a position downstream of the connection position with the bypass passage 70 in the second intake passage 20.

The first throttle valve 12 adjusts the flow rate of gas passing through the first throttle valve 12 by adjusting the opening degree of the valve body. The first throttle valve 12 operates in response to the control signal C1 from the ECU 100. The first throttle valve 12 has, for example, a small opening degree for flowing EGR gas from the EGR passage 80 to the intake manifold, or a small opening degree for stopping combustion when the operation of the engine 2 is stopped. It is controlled to increase the pumping loss according to the accelerator off operation and reduce the opening degree in order to act the engine brake when the vehicle is running under heavy load.

The other end of the bypass passage 70 is connected to a third exhaust passage 42 connecting the three-way catalyst 60 and the PM removal filter 62. A second throttle valve 72 and a check valve 74 are provided in the middle of the bypass passage 70.

The check valve 74 is provided in the bypass passage 70 at a position on the other end side of the bypass passage 70 with respect to the second throttle valve 72, and suppresses the backflow of gas from the other end to one end. The check valve 74 may be provided in the bypass passage 70, and is not particularly limited to the position shown in FIG.

The second throttle valve 72 is switched from one of the valve open state and the valve closed state to the other state according to the control signal C2 from the ECU 100. When the second throttle valve 72 is in the closed state, the flow of air from the second intake passage 20 to the bypass passage 70 is suppressed. On the other hand, when the second throttle valve 72 is in the closed state, air flow from the second intake passage 20 to the bypass passage 70 is allowed.

One end of the EGR passage 80 is connected to a position downstream of the position where the first throttle valve 12 is provided in the second intake passage 20. The other end of the EGR passage 80 is connected in the middle of the first exhaust passage 30. An EGR valve 82 is provided in the middle of the EGR passage 80.

The EGR valve 82 adjusts the flow rate of the gas passing through the EGR valve 82 by adjusting the opening degree of the valve body. The EGR valve 82 operates in response to the control signal C3 from the ECU 100.

A second pressure gauge 204 is provided at a position between the second throttle valve 72 and the check valve 74 in the bypass passage 70. The second pressure gauge 204 detects the pressure of the gas flowing through the bypass passage 70 (hereinafter referred to as the second pressure). The second pressure gauge 204 transmits a signal indicating the detected second pressure to the ECU 100.

The TWC 60 is connected to the other end of the second exhaust passage 40, one end of which is connected to the turbine 54. The TWC60 simultaneously oxidizes and reduces harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust with a catalyst using platinum, palladium, and rhodium. Remove. Specifically, the TWC 60 oxidizes hydrocarbons to water and carbon dioxide, oxidizes carbon monoxide to carbon dioxide, and reduces nitrogen oxides to nitrogen. In order to appropriately purify (oxidize and reduce) harmful substances contained in the exhaust gas with the TWC 60, the engine 2 is operated in a stoichiometric state in which the air-fuel ratio becomes the stoichiometric air-fuel ratio. Further, the TWC 60 has a function of occluding oxygen components in the exhaust when the air-fuel ratio of the exhaust is in a lean state, and releasing the stored oxygen when the air-fuel ratio of the exhaust is in a rich state. ing.

The PM removal filter 62 collects particulate matter (hereinafter referred to as PM (Particulate Matter)) such as soot contained in the exhaust gas flowing from the third exhaust passage 42. The PM removal filter 62 is made of, for example, ceramic or the like. The collected PM is deposited in the PM removal filter 62.

The NOx purification catalyst 64 includes, for example, an SCR (Selective Catalytic Reduction) catalyst. The SCR catalyst is activated by being supplied with urea water as a reducing agent, and selectively reduces NOx in the exhaust gas. An addition valve (not shown) for adding urea water is provided upstream of the SCR catalyst. When urea water is added by the addition valve, the added urea water is hydrolyzed by the heat of the exhaust gas in the SCR catalyst and converted into ammonia. The chemical reaction between the changed ammonia and NOx in the exhaust gas reduces it to nitrogen and water, purifying the exhaust gas. The add-on valve is controlled according to a control signal from the ECU 100.

The NOx purification catalyst 64 may include an NSR (NOx Storage-Reduction) catalyst in place of or in addition to the SCR catalyst. The NSR catalyst absorbs NOx in a state where a large amount of oxygen is present in the exhaust gas (lean state), the oxygen concentration in the exhaust gas is low, and a reducing agent (for example, unburned components (HC and CO) of the fuel). ) Is present in a large amount, NOx is reduced to _N2 and released. By reducing NO ₂ and NO, HC and CO are themselves oxidized to H ₂ O and CO ₂ . That is, if the oxygen concentration in the exhaust gas, the HC component, and the CO component introduced into the NSR catalyst are appropriately adjusted, the HC, CO, and NOx in the exhaust gas can be purified.

An atmospheric pressure gauge 206 is connected to the ECU 100. Atmospheric pressure gauge 206 detects atmospheric pressure. The atmospheric pressure gauge 206 transmits a signal indicating the detected atmospheric pressure to the ECU 100.

The operation process of the engine 2 is executed by the ECU 100. The ECU 100 is a control including a CPU (Central Processing Unit) that performs various processes, a ROM (Read Only Memory) that stores programs and data, and a memory that includes a RAM (Random Access Memory) that stores the processing results of the CPU and the like. It is a device.

The ECU 100 determines that the engine 2 is in a desired operating state based on signals from each measuring device (eg, flow meter 200, first pressure gauge 202 and second pressure gauge 204), as well as maps and programs stored in memory. Control various devices so that The various processes executed by the ECU 100 are not limited to the processes by software, but can also be processed by dedicated hardware (electronic circuit).

The ECU 100 includes an engine control unit 102, a flow rate calculation unit 104, and a valve control unit 106.

The engine control unit 102 executes processing for controlling the engine 2 and the like. Specifically, the engine control unit 102 controls the engine 2 by using the information from the flow rate calculation unit 104, the valve control unit 106, and the atmospheric pressure gauge 206.

For example, the engine control unit 102 commands the fuel injection device based on the amount of air sucked into the engine 2 so that the air-fuel ratio of the exhaust of the engine 2 becomes the target air-fuel ratio (for example, a value indicating stoichiometry). Set the amount.

The engine control unit 102 calculates, for example, the amount of air sucked into the engine 2 from the flow rate of the air flowing through the bypass passage 70 and the amount of intake air. The engine control unit 102 acquires, for example, the intake air amount from the valve control unit 106. Further, the engine control unit 102 acquires the atmospheric pressure from the atmospheric pressure gauge 206.

Further, the engine control unit 102 sets a target EGR rate based on, for example, the operating state of the engine 2, and controls the valve with information on the opening degree of the EGR valve 82 calculated from the set target EGR rate or the target EGR rate. Output to unit 106. Further, the engine control unit 102 controls the operation of the turbocharger 50 by using, for example, the first pressure.

The flow rate calculation unit 104 executes a process of calculating the flow rate of the air flowing through the bypass passage 70. The flow rate calculation unit 104 acquires the first pressure by using, for example, the first pressure gauge 202. Further, the flow rate calculation unit 104 acquires the second pressure by using, for example, the second pressure gauge 204.

The flow rate calculation unit 104 calculates the flow rate of the air flowing through the bypass passage 70 by using, for example, the difference (pressure difference) between the first pressure and the second pressure. The flow rate calculation unit calculates the flow rate of the air flowing through the bypass passage 70 by using the pressure difference, the passage cross-sectional area of the second intake passage 20, the passage cross-sectional area of the bypass passage 70, and the like. As for the method of calculating the flow rate using the pressure difference, a well-known method may be used, and the detailed description thereof will not be given.

The flow rate calculation unit 104 outputs information on the calculated flow rate of air flowing through the bypass passage 70 and information on the first pressure to the engine control unit 102.

The valve control unit 106 executes processing for controlling the first throttle valve 12, the second throttle valve 72, and the EGR valve 82. The valve control unit 106 controls to control the first throttle valve 12, the second throttle valve 72, and the EGR valve 82 by using the intake air amount acquired by the flow meter 200 and the information received from the engine control unit 102. Signals C1 to C3 are output to each valve. The valve control unit 106 controls the first throttle valve 12 and the EGR valve 82 based on, for example, information regarding the target EGR rate and the opening degree of the EGR valve 82 received from the engine control unit 102.

In the engine system 1 having the above configuration, the turbocharger 50 is required to operate within a predetermined operating region so that the operating state of the turbocharger 50 does not enter the surge region. The surge region is a region where the pressure ratio between the boost pressure and the atmospheric pressure is high and the intake air amount is small. Therefore, for example, a bypass passage connecting the passage downstream of the compressor 52 of the supercharger 50 and the second exhaust passage 40 downstream of the turbine 54 is provided so that the operating state of the supercharger 50 does not enter the surge region. It is conceivable to provide the bypass passage through a valve or the like when the operating region of the turbocharger 50 becomes a surge region. With such a configuration, the pressure ratio can be lowered by lowering the pressure downstream of the compressor 52. Therefore, it is possible to prevent the operating region of the turbocharger 50 from becoming a surge region.

However, when the gas downstream of the compressor 52 is circulated to the second exhaust passage 40 downstream of the turbine 54 via the bypass passage, the air is mixed with the exhaust supplied to the plurality of exhaust treatment devices downstream of the turbine 54. Because the temperature of the exhaust gas drops and the air fuel ratio changes, depending on the exhaust treatment device, the exhaust gas is properly purified in each of the multiple exhaust gas treatment devices due to the change in the air fuel ratio and the decrease in temperature. You may not be able to do it.

Therefore, in the present embodiment, the engine system 1 includes a bypass passage 70 and a second throttle valve 72, and the ECU 100 is supercharged by the supercharger 50 when a predetermined condition is satisfied. It is assumed that the second throttle valve 72 is controlled so as to be in the valve open state in the state of being open. Further, in the present embodiment, the predetermined condition is within the range in which the operating region of the turbocharger 50 indicated by the pressure ratio in the compressor and the intake air amount includes the surge region and the predetermined first region. It shall include the condition that it is.

In this way, when a predetermined condition is satisfied, the second throttle valve 72 is opened in the state of being supercharged by the supercharger 50, so that the space between the compressor 52 and the engine 2 is reached. Since a part of the gas flowing through the compressor 52 can be circulated downstream of the turbine 54 via the bypass passage 70, it is possible to prevent the operating region of the compressor 52 from becoming a surge region. Further, by supplying air from the bypass passage 70, the air-fuel ratio of the exhaust becomes lean on the downstream side of the third exhaust passage 42. Therefore, in the TWC 60, the air-fuel ratio does not change due to the air supplied from the bypass passage 70, and the air-fuel ratio of the PM removal filter 62 and the NOx purification catalyst 64 is changed by the air supplied from the bypass passage 70. Exhaust that becomes lean is supplied. As a result, while suppressing the deterioration of the purification performance of the TWC 60, the PM removal filter 62 burns soot to enable regeneration, and the NOx purification catalyst 64 purifies NOx to purify each exhaust gas treatment device. It is possible to suppress the deterioration of purification performance.

Hereinafter, the process executed by the ECU 100 in the first embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing an example of processing executed by the ECU 100 in the first embodiment. The process shown in this flowchart is called and executed from the main routine (not shown) at predetermined control cycles.

At step 100 (hereinafter, step is referred to as S) 100, the ECU 100 acquires the intake air amount, the first pressure, and the atmospheric pressure. The ECU 100 acquires the intake air amount by using the flow meter 200. The ECU 100 acquires the first pressure by using the first pressure gauge 202. The ECU 100 acquires the atmospheric pressure using the atmospheric pressure gauge 206.

In S102, the ECU 100 calculates the operating point of the turbocharger 50. The ECU 100 calculates the pressure ratio of the compressor 52 from the acquired first pressure and the atmospheric pressure. The ECU 100 calculates the calculated pressure ratio of the compressor 52 and the intake air amount as the operating points of the turbocharger 50.

In S104, the ECU 100 determines whether or not the operating point of the turbocharger 50 is within a predetermined range.

FIG. 3 is a diagram showing an example of a predetermined range of operating points of the turbocharger 50. The horizontal axis of FIG. 3 indicates the intake air amount. The vertical axis of FIG. 3 shows the pressure ratio in the compressor 52. The solid line frame shown by LN1 in FIG. 3 indicates an area set as an operating area of the turbocharger 50. The shaded area shown by LN2 in FIG. 3 indicates a predetermined range set as an operating area of the turbocharger 50 that executes control to open the second throttle valve 72. LN3 in FIG. 3 shows an overlapping portion between a predetermined range and a region shown by a solid line frame of LN1 in FIG.

The predetermined range includes, for example, a surge region and an overlapping portion shown by LN3 in FIG. That is, the overlapping portion shown by LN3 in FIG. 3 corresponds to the "first region adjacent to the boundary on the intake air amount side of the surge region". Further, the region shown by the solid line frame of LN1 in FIG. 3 corresponds to the "predetermined second region including the first region".

The ECU 100 determines whether or not the calculated operating point of the turbocharger 50 is within the predetermined range shown by LN2 in FIG. When it is determined that the operating point of the turbocharger 50 is within the predetermined range shown by LN2 in FIG. 3 (YES in S104), the process is transferred to S106.

In S106, the ECU 100 controls the second throttle valve 72 so that the valve is opened. When the second throttle valve 72 is opened, the ECU 100 turns on a flag indicating that the second throttle valve 72 is in the opened state.

In S108, the ECU 100 acquires the first pressure and the second pressure. The ECU 100 acquires the first pressure by using the first pressure gauge 202 and acquires the second pressure by using the second pressure gauge 204. The ECU 100 may acquire the first pressure and the second pressure after a predetermined time for the pressure change to converge has elapsed after the second throttle valve 72 is opened.

In S110, the ECU 100 calculates the flow rate of air passing through the bypass passage 70. The ECU 100 calculates the flow rate of air passing through the bypass passage 70 by using the difference between the first pressure and the second pressure.

In S112, the ECU 100 controls the engine 2 so that the air-fuel ratio becomes the target air-fuel ratio. The ECU 100 calculates the amount of air flowing through the engine 2 from the flow rate of air passing through the bypass passage 70 and the amount of intake air, and the air-fuel ratio of the exhaust of the engine 2 becomes the target air-fuel ratio with respect to the calculated air amount. The fuel injection amount is set so as to be. The target air-fuel ratio may be, for example, a value indicating stoichiometry. The ECU 100 controls the fuel injection device so that the fuel of the set fuel injection amount is injected.

When it is determined that the operating point of the turbocharger 50 is not within the predetermined range shown by LN2 in FIG. 3 (NO in S104), the process is transferred to S114.

In S114, the ECU 100 determines whether or not the second throttle valve 72 is in the valve open state. The ECU 100 determines that the second throttle valve 72 is in the open state, for example, when the flag indicating that the second throttle valve 72 is in the open state is on. When it is determined that the second throttle valve 72 is in the valve open state (YES in S114), the process is transferred to S116.

In S116, the ECU 100 controls the second throttle valve 72 so that the valve is closed. At this time, when the second throttle valve 72 is closed, the ECU 100 turns off the flag indicating that the second throttle valve 72 is in the open state.

When it is determined that the second throttle valve 72 is not in the valve open state (NO in S114), this process is terminated.

The operation of the ECU 100 based on the above structure and the flowchart will be described with reference to FIG.

FIG. 4 is a diagram for explaining a change in the operating point of the turbocharger 50 due to the operation of the ECU 100. The horizontal axis of FIG. 4 indicates the intake air amount. The vertical axis of FIG. 4 shows the pressure ratio in the compressor 52. The solid line frame shown by LN1 in FIG. 4 indicates a region set as an operating area of the turbocharger 50, similarly to the solid line frame shown by LN1 in FIG. The shaded area shown by LN2 in FIG. 4 is set as an operating area of the turbocharger 50 that executes control to open the second throttle valve 72, similarly to the shaded area shown by LN2 in FIG. Indicates a predetermined range. The shaded area shown by LN3 in FIG. 4 shows an overlapped portion between the predetermined range and the region shown by the solid line frame of LN1 in FIG. 4, similarly to the shaded area shown by LN3 in FIG.

For example, when the intake air amount detected by the flow meter 200, the first pressure detected by the first pressure gauge 202, and the atmospheric pressure detected by the atmospheric pressure gauge 206 are acquired by the ECU 100 (S100), the acquisition is performed. The operating point of the turbocharger 50 is calculated from the sucked air amount, the first pressure, and the atmospheric pressure (S102). For example, when the point A in FIG. 4 is calculated as the operating point of the turbocharger 50, it is determined that the operating point of the turbocharger 50 is within the predetermined range indicated by the shaded area of LN2 in FIG. 4 (in S104). YES), the second throttle valve 72 is controlled so as to be in the valve open state (S106).

When the second throttle valve 72 is opened, a part of the air flowing out from the compressor 52 passes through the second throttle valve 72, flows to the third exhaust passage 42 via the bypass passage 70, and other parts. The portion is distributed to the engine 2. As a result, the operating point of the turbocharger 50 is suppressed from changing from the point A in FIG. 4 to the point B in the surge region. Therefore, as shown by the arrow from point A in FIG. 4, the operating point of the turbocharger 50 changes to point C while maintaining the area indicated by the solid line frame of LN1 in FIG. 4 without entering the surge region. .. As a result, the turbocharger 50 is suppressed from operating in the surge region. Since the check valve 74 is provided in the bypass passage 70, gas flows from the third exhaust passage 42 side to the second intake passage 20 side in the bypass passage 70 while the second throttle valve 72 is in the valve open state. Backflow is suppressed.

After that, the first pressure and the second pressure are acquired (S108), and the flow rate of the air flowing through the bypass passage 70 is calculated using the difference between the first pressure and the second pressure (S110). Then, when the amount of air flowing into the engine 2 is calculated using the calculated air flow rate, the air-fuel ratio of the exhaust gas from the engine 2 is set to the target air-fuel ratio (for example, the stoichiometric state) using the calculated air amount. The engine 2 is controlled so as to be (the value shown) (S112).

Since the exhaust gas whose air-fuel ratio is a value indicating the stoichiometric state is supplied to the TWC60, HC (hydrogen dioxide), CO (carbon monoxide) and NOx (nitrogen oxides) contained in the exhaust gas are appropriately purified and at the same time. Exhaust gas having an air-fuel ratio of a value indicating a lean state is supplied to the PM removal filter 62 and the NOx purification catalyst 64 by the air supplied through the bypass passage 70. As a result, the PM deposited in the PM removal filter 62 is easily burned, and the NOx purification catalyst 64 promotes the purification of NOx.

Then, when the intake air amount, the first pressure, and the atmospheric pressure are acquired (S100) and the point C is calculated as the operating point of the turbocharger 50 using the acquisition results, it is determined that the point C is not within the predetermined range (S104). Since NO), the second throttle valve 72 is in the open state (YES in S114), so that the second throttle valve 72 is controlled so as to be in the closed state (S116).

As described above, according to the engine system 1 according to the present embodiment, when the condition that the operating point of the supercharger 50 is within the predetermined range is satisfied, the turbocharger 50 is supercharged. The second throttle valve 72 is opened. Therefore, a part of the gas flowing between the compressor 52 and the engine 2 can be circulated downstream of the turbine 54 via the bypass passage 70, so that the operating region of the turbocharger 50 becomes a surge region. Can be suppressed. Further, the air-fuel ratio of the exhaust becomes lean due to the supply of air from the bypass passage 70. Therefore, in the TWC 60, the air-fuel ratio does not change due to the air supplied from the bypass passage 70, and the air-fuel ratio of the PM removal filter 62 and the NOx purification catalyst 64 is due to the air supplied from the bypass passage 70. Is supplied with lean exhaust. As a result, while suppressing the deterioration of the purification performance of the TWC 60, the PM removal filter 62 burns soot to enable regeneration, and the NOx purification catalyst 64 purifies NOx to purify each exhaust gas treatment device. It is possible to suppress the deterioration of purification performance. Therefore, it is possible to provide an engine system that suppresses the deterioration of the exhaust gas purification performance of the exhaust gas treatment device while suppressing the operating state of the turbocharger from entering the surge region.

Further, the flow rate of the gas flowing through the bypass passage 70 is calculated using the difference between the first pressure and the second pressure, and the flow rate of the gas flowing through the engine 2 is calculated using the calculated flow rate. The fuel injection amount of 2 can be appropriately adjusted, and the air-fuel ratio of the exhaust can be adjusted to an appropriate air-fuel ratio (target air-fuel ratio).

Further, since the check valve 74 is provided in the bypass passage 70, it is possible to suppress the backflow of gas from the exhaust side to the intake side via the bypass passage 70.

Further, since the TWC 60 is provided as an exhaust treatment device on the upstream side of the third exhaust passage 42 to which air is supplied from the bypass passage 70, the TWC 60 is excluded from the air supply target via the bypass passage 70. Therefore, it is possible to prevent the air-fuel ratio of the exhaust gas supplied to the TWC 60 from changing to the lean side and to prevent the temperature from dropping unnecessarily. As a result, it is possible to suppress a decrease in the exhaust gas purification performance of the TWC60.

Hereinafter, modification examples will be described.
In the above-described embodiment, the second throttle valve 72 has been described as switching from one of the valve open state and the valve closed state to the other state, but the second throttle valve 72 is described. The opening may be configured to be adjustable. By doing so, for example, the opening degree of the second throttle valve 72 can be adjusted so that the flow rate of the gas flowing through the bypass passage 70 becomes the target flow rate. Therefore, by appropriately setting the target flow rate, the amount of air supplied to the exhaust treatment device on the downstream side of the third exhaust passage 42 can be adjusted to an appropriate amount. Therefore, it is possible to suppress deterioration of the exhaust purification performance of the exhaust gas treatment device on the downstream side. Alternatively, by increasing the opening as the operating point of the turbocharger 50 is closer to the surge region, it is possible to prevent the operating point of the turbocharger 50 from becoming the surge region and unnecessarily increase the boost pressure. It is possible to suppress the decrease.

Further, in the above-described embodiment, when the operating point of the turbocharger 50 is within a predetermined range, the second throttle valve 72 is controlled so as to be in the valve open state. When the change direction of the operating point of the turbocharger 50 is in the direction approaching the surge region (for example, the direction in which the intake air amount decreases), the valve is opened so as to be in the second valve state. The throttle valve 72 may be controlled. By doing so, it is possible to prevent the operating point of the turbocharger 50 from becoming a surge region and to prevent the supercharging pressure from being unnecessarily reduced.

Further, in the above-described embodiment, when the operating point of the turbocharger 50 is within a predetermined range, the second throttle valve 72 is controlled so as to be in the valve open state. When the opening degree of the first throttle valve 12 is within the range of the above and the opening degree of the first throttle valve 12 is equal to or less than the threshold value, the second throttle valve 72 may be controlled so as to be in the valve open state. By doing so, it is possible to prevent the operating point of the turbocharger 50 from becoming a surge region.

Further, in the above-described embodiment, the flow rate calculation unit 104 has been described as calculating the flow rate of the air flowing through the bypass passage 70 from the difference between the first pressure and the second pressure, but the opening of the second throttle valve 72 has been described. If the degree can be adjusted, the flow rate of the air flowing through the bypass passage 70 may be calculated as follows. That is, a map showing the relationship between the first pressure, the opening degree of the second throttle valve 72, and the flow rate of the air flowing through the bypass passage 70 is created by an experiment or the like, and the flow rate calculation unit 104 uses the first pressure. And, the flow rate of the air flowing through the bypass passage 70 may be calculated from the opening degree of the second throttle valve 72 and the above map.

Further, in the above-described embodiment, the configuration in which the TWC 60 is provided as the exhaust treatment device on the upstream side of the third exhaust passage 42 to which the air from the bypass passage 70 is supplied has been described as an example, but the exhaust treatment on the upstream side has been described. The device is not particularly limited to the TWC60. The exhaust gas treatment device on the upstream side may include, for example, TWC60, an oxidation catalyst (hereinafter referred to as DOC (Diesel Oxidation Catalyst)), a PM removal filter, and at least one of a NOx purification catalyst. good.

Hereinafter, a configuration in which the DOC is provided in place of the TWC 60 in the engine system 1 will be described as an example of a modification.

FIG. 5 is a diagram showing an example of a schematic configuration of an engine system 1 according to a modified example of the first embodiment. The configuration of the engine system 1 shown in FIG. 5 differs from the configuration of the engine system 1 shown in FIG. 1 in that the DOC 66 is provided instead of the TWC 60. Other configurations are the same as the configuration of the engine system 1 shown in FIG. 1, and the same reference numerals are given. Therefore, the detailed description of their configuration will not be repeated.

The DOC 66 is connected to the other end of the second exhaust passage 40. The DOC 66 is made of a cell-shaped cylinder formed of a ceramic columnar or the like, and a large number of through holes are formed in the axial direction thereof, and a precious metal such as platinum (Pt) is coated on the inner surface thereof. The DOC 66 oxidizes and removes carbon monoxide, hydrocarbons, and the like contained in the exhaust gas by passing the exhaust gas through a large number of through holes under a predetermined temperature.

In the engine system 1 having such a configuration, the ECU 100 executes the process shown in the flowchart of FIG. Since the processing shown in the flowchart of FIG. 2 is as described above, the detailed description thereof will not be repeated.

The operation of the ECU 100 based on the above structure and the flowchart will be described.

For example, the intake air amount, the first pressure, and the atmospheric pressure are acquired (S100), and the operating point of the turbocharger 50 is calculated from the acquired intake air amount, the first pressure, and the atmospheric pressure (S102). ). When it is determined that the calculated operating point of the turbocharger 50 is within the predetermined range (YES in S104), the second throttle valve 72 is controlled so as to be in the valve open state (S106).

When the second throttle valve 72 is opened, a part of the air flowing out from the compressor 52 passes through the second throttle valve 72 and flows to the third exhaust passage 42 via the bypass passage 70. As a result, the operating point of the turbocharger 50 changes while being maintained within a predetermined range without entering the surge region. As a result, the turbocharger 50 is suppressed from operating in the surge region.

After that, the first pressure and the second pressure are acquired (S108), and the flow rate of the air flowing through the bypass passage 70 is calculated using the difference between the first pressure and the second pressure (S110). Then, the control of the engine 2 is executed using the calculated flow rate of air (S112).

Exhaust gas having an air-fuel ratio of a value indicating a lean state is supplied to the PM removal filter 62 and the NOx purification catalyst 64 by the air supplied through the bypass passage 70. As a result, the PM deposited in the PM removal filter 62 is easily burned, and the NOx purification catalyst 64 promotes the purification of NOx.

On the other hand, since the air supplied to the third exhaust passage 42 via the bypass passage 70 is not supplied to the DOC 66, it is suppressed that the temperature of the DOC 66 is lowered by the air flowing through the bypass passage 70.

FIG. 6 is a diagram for explaining an example of a temperature change of the DOC 66 in the modified example of the first embodiment. The horizontal axis of FIG. 6 indicates time. The vertical axis of FIG. 6 shows the floor temperature of DOC66 (hereinafter, also referred to as catalyst floor temperature). LN4 (solid line) in FIG. 6 shows the temperature change of the DOC 66 in the engine system 1 according to this modification. LN5 (dashed line) in FIG. 6 shows the temperature change of the DOC 66 when the other end of the bypass passage 70 is connected to the second exhaust passage 40. The catalyst bed temperature Tc (0) indicates the lower limit of the temperature at which the catalyst is activated.

For example, when the second throttle valve 72 is opened at time t (0), air flows through the bypass passage 70. When the other end of the bypass passage 70 is connected to the second exhaust passage 40, as shown in LN5 of FIG. 6, the air flowing from the other end of the bypass passage 70 to the second exhaust passage 40 is supplied to the DOC 66. , The temperature of the DOC66 decreases due to the supplied air. Then, at time t (1), the temperature of DOC66 falls below the catalyst bed temperature Tc (0), and the purification performance of the exhaust gas of DOC66 deteriorates.

On the other hand, in the engine system 1 according to this modification, when the other end of the bypass passage 70 is connected to the third exhaust passage 42, the air flowing from the other end of the bypass passage 70 to the third exhaust passage 42. Is not supplied to the DOC66, so that the temperature of the DOC66 is maintained higher than the catalyst bed temperature Tc (0), as shown in LN4 of FIG. Therefore, it is possible to suppress a decrease in the purification performance of the DOC 66.

Similarly, when a PM removal filter is provided instead of the TWC60 and when a NOx purification catalyst is provided, the temperature of each exhaust gas treatment device can be maintained within an activating temperature range, so that purification is possible. It is possible to suppress the deterioration of performance.

Further, in the above-described embodiment, the case where the supercharger 50 is a turbocharger has been described as an example, but the supercharger 50 is, for example, a supercharger in which the compressor is driven by the power of the engine 2. It may be an electric turbocharger in which the compressor is operated by a motor.

Further, in the above-described embodiment, the exhaust gas treatment device downstream from the position where the other end of the bypass passage 70 is connected includes the PM removal filter 62 and the NOx purification catalyst 64, but the PM removal filter has been described. In addition to or in place of 62 and the NOx purification catalyst 64, at least one of a three-way catalyst and an oxidation catalyst may be provided as a downstream exhaust treatment device.

In addition, the above-mentioned modification may be carried out by combining all or a part thereof.
<Second embodiment>
In the first embodiment, when the predetermined condition that the operating point of the turbocharger 50 is within the predetermined range is satisfied, the valve is opened in the state of being supercharged by the turbocharger 50. The second throttle valve 72 was controlled so as to be. On the other hand, in the second embodiment, the ECU 100 is opened in a state of being supercharged by the supercharger 50 when predetermined conditions for the oxygen storage amount and the air-fuel ratio in the TWC 60 are satisfied. It is assumed that the second throttle valve 72 is controlled so as to be in a valve state.

FIG. 7 is a diagram showing an example of a schematic configuration of the engine system 1 according to the second embodiment. In the configuration of the engine system 1 according to the second embodiment shown in FIG. 7, the atmospheric pressure meter 206 is omitted as compared with the configuration of the engine system 1 according to the first embodiment shown in FIG. It is different in that it includes an air-fuel ratio meter 208 and that the turbine 54 includes a variable nozzle mechanism 58. Other configurations are the same as the configuration of the engine system 1 shown in FIG. 1, and the same reference numerals are given. Therefore, the detailed description of their configuration will not be repeated.

The air-fuel ratio meter 208 is connected to the ECU 100. The air-fuel ratio meter 208 detects the air-fuel ratio of the exhaust gas flowing through the second exhaust passage 40. The air-fuel ratio meter 208 transmits a signal indicating the detected air-fuel ratio to the ECU 100.

The variable nozzle mechanism 58 changes the flow velocity of the exhaust gas that operates the turbine 54. The variable nozzle mechanism 58 is arranged on the outer peripheral side of the turbine wheel of the turbine 54, and rotates a plurality of nozzle vanes (not shown) that guide the exhaust gas supplied from the exhaust inlet to the turbine wheel, and each of the plurality of nozzle vanes. Includes a drive device (not shown) that changes the gap between adjacent nozzle vanes (hereinafter referred to as VN opening degree). The variable nozzle mechanism 58 changes the VN opening degree by rotating the nozzle vane using, for example, a drive device that operates in response to the control signal C4 from the ECU 100. For example, by controlling the VN opening degree to be small, the gap between adjacent nozzle vanes becomes small. Therefore, the flow velocity of the exhaust gas increases, and the rotational speed of the turbine wheel is increased, so that the boost pressure can be increased. Similarly, by greatly controlling the VN opening degree, the flow velocity of the exhaust gas is reduced, and the rotational speed of the turbine wheel is reduced, so that the boost pressure can be reduced.

In such a configuration, in the present embodiment, in the ECU 100, the oxygen storage amount in the TWC 60 is equal to or less than the threshold value, and the air-fuel ratio of the exhaust gas detected by the air-fuel ratio meter 208 is in a stoichiometric state or a rich state. When the predetermined condition of the indicated value is satisfied, the second throttle valve 72 is controlled so as to be in the valve open state in the state of being supercharged by the supercharger 50.

In this way, since the air-fuel ratio of the exhaust gas of the engine 2 is a value indicating a stoichiometric state or a rich state, the exhaust gas treatment device on the upstream side of the connection position between the other end of the bypass passage 70 and the third exhaust passage 42 Exhaust components such as HC, CO and NOx can be purified in the contained three-way catalyst. Further, if the oxygen storage amount in the TWC 60 is low, oxygen is not discharged from the TWC 60, but air is supplied to the exhaust treatment device on the downstream side of the connection position via the bypass passage 70, so that the exhaust on the downstream side is exhausted. It is possible to improve the exhaust gas purification performance of the PM removal filter 62 and the NOx purification catalyst 64 included in the processing apparatus. Therefore, PM is easily burned in the PM removal filter 62, and NOx purification is promoted in the NOx purification catalyst 64.

Hereinafter, the process executed by the ECU 100 in the second embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing an example of the process executed by the ECU 100 in the second embodiment. The process shown in this flowchart is called from the main routine and executed every predetermined control cycle.

In S200, the ECU 100 acquires the first pressure and the air-fuel ratio. The ECU 100 acquires the first pressure by using the first pressure gauge 202. The ECU 100 acquires the air-fuel ratio by using the air-fuel ratio meter 208.

In S202, the ECU 100 estimates the oxygen storage amount of the TWC60. The ECU 100 estimates the oxygen storage amount of the TWC 60 by using, for example, the operation history of the engine 2 including the air-fuel ratio.

For example, when the air-fuel ratio is in a lean state, the ECU 100 stores an excess amount of oxygen in a predetermined period (for example, a control cycle), so that the amount of increase in the amount of oxygen stored is increased from the air-fuel ratio. presume. The ECU 100 calculates the estimated value of the stored amount this time by adding the increased amount of the estimated stored amount of oxygen to the estimated value of the previous stored amount. Similarly, for example, when the air-fuel ratio is in a rich state, the ECU 100 estimates the decrease in the amount of oxygen stored from the air-fuel ratio because the insufficient oxygen is discharged. The ECU 100 calculates the estimated value of the stored amount this time by adding the amount of decrease in the estimated stored amount of oxygen to the estimated value of the previous stored amount. In addition to the air-fuel ratio, the operating state of the engine 2 may be taken into consideration in the estimation of the increase and the estimation of the decrease.

In S204, the ECU 100 determines whether or not the oxygen storage amount is equal to or less than the threshold value and the air-fuel ratio is a value indicating a stoichiometric state or a rich state. The threshold value is, for example, a value for determining a state in which the oxygen storage amount is insufficient. The threshold value may be, for example, zero or a value larger than zero, and is a predetermined value adapted by experiments or the like. When the oxygen storage amount is equal to or less than the threshold value and the air-fuel ratio is determined to be a value indicating a stoichiometric state or a rich state (YES in S204), the process is transferred to S206.

In S206, the ECU 100 executes the boost pressure increase control. The ECU 100 controls, for example, the variable nozzle mechanism 58 so that the first pressure exceeds the threshold value. The ECU 100 controls, for example, the variable nozzle mechanism 58 so that the opening degree corresponds to the difference between the first pressure and the threshold value. The ECU 100 sets the opening degree by using, for example, a map showing the relationship between the difference between the first pressure and the threshold value and the VN opening degree, and controls the variable nozzle mechanism 58 so as to have the set opening degree. .. The threshold value may be at least a pressure at which air can flow to the third exhaust passage 42 via the bypass passage 70, and is not particularly limited, and is, for example, a predetermined value. The ECU 100 maintains the control state of the variable nozzle mechanism 58 when the first pressure exceeds the threshold value.

In S208, the ECU 100 controls the second throttle valve 72 so that the valve is opened. When the second throttle valve 72 is opened, the ECU 100 turns on a flag indicating that the second throttle valve 72 is in the opened state.

In S210, the ECU 100 acquires the first pressure and the second pressure. The ECU 100 acquires the first pressure by using the first pressure gauge 202 and acquires the second pressure by using the second pressure gauge 204. It is desirable that the ECU 100 acquires the first pressure and the second pressure after a predetermined time for the pressure change to converge after the second throttle valve 72 is opened.

In S212, the ECU 100 calculates the flow rate of air passing through the bypass passage 70. The ECU 100 calculates the flow rate of air passing through the bypass passage 70 using the pressure difference between the first pressure and the second pressure.

In S214, the ECU 100 controls the engine 2 so that the air-fuel ratio becomes the target air-fuel ratio. The specific control method is the same as the control method of the engine 2 shown in the process of S112 in the flowchart of FIG. 2 in the first embodiment described above. Therefore, the detailed explanation will not be repeated.

If the oxygen storage amount is larger than the threshold value or the air-fuel ratio is a value indicating a lean state (NO in S204), the process is transferred to S216.

In S216, the ECU 100 determines whether or not the second throttle valve 72 is in the valve open state. The ECU 100 determines that the second throttle valve 72 is in the open state when the flag indicating that the second throttle valve 72 is in the open state is on. When it is determined that the second throttle valve 72 is in the valve open state (YES in S216), the process is transferred to S218.

In S218, the ECU 100 controls the second throttle valve 72 so that the valve is closed. For example, when the second throttle valve 72 is closed, the ECU 100 turns off the flag indicating that the second throttle valve 72 is in the open state.

When it is determined that the second throttle valve 72 is not in the valve open state (NO in S216), this process is terminated.

The operation of the ECU 100 based on the above structure and the flowchart will be described with reference to FIG. FIG. 9 is a timing chart showing changes in the air-fuel ratio, oxygen storage amount, and NOx emission amount. The horizontal axis of FIG. 9 indicates time. The vertical axis of FIG. 9 shows the air-fuel ratio, the oxygen occlusion amount, and the NOx emission amount. LN6 in FIG. 9 shows the change in the air-fuel ratio. LN7 in FIG. 9 shows the change in oxygen storage amount. LN8 in FIG. 9 shows a change in the amount of NOx discharged from the NOx purification catalyst 64 when the second throttle valve 72 is not opened when the oxygen storage amount decreases. LN9 in FIG. 9 shows a change in the amount of NOx discharged from the NOx purification catalyst 64 when the second throttle valve 72 is opened when the oxygen storage amount decreases.

When the first pressure and the air-fuel ratio are acquired (S200), the oxygen storage amount of the TWC 60 is estimated using the operation history of the engine 2 including the air-fuel ratio (S202).

For example, as shown in LN6 before the time t (2) in FIG. 9, when the air-fuel ratio of the exhaust gas from the engine 2 is a value indicating a lean state and the oxygen storage amount is the upper limit value in the TWC60 ( NO in S204), the closed state of the second throttle valve 72 is maintained (NO in S216). At this time, since the air-fuel ratio of the exhaust gas is in a lean state, the increase in NOx emissions is suppressed by purifying NOx in each of the TWC 60 and the NOx purification catalyst 64.

When the air-fuel ratio of the exhaust gas becomes rich due to a change in the operating state of the engine 2 at time t (2), oxygen occluded in the TWC 60 is supplied, and the catalyst surface of the TWC 60 is maintained in a stoichiometric state. Purification of HC, CO and NOx is performed. As a result, the amount of oxygen stored in the TWC 60 will decrease.

Then, at time t (3), when the air-fuel ratio of the exhaust remains rich and the oxygen storage amount becomes equal to or less than the threshold value (YES in S204), the boost pressure increase control is executed to perform the first step. The variable nozzle mechanism 58 is controlled so that the pressure exceeds the threshold value (S206), and the second throttle valve 72 is opened (S208). Then, when the first pressure and the second pressure are acquired (S210), the flow rate of the air flowing through the bypass passage 70 is calculated using the acquired pressure difference between the first pressure and the second pressure (S210). S212). The control of the engine 2 is executed using the calculated air flow rate (S214).

Exhaust gas having an air-fuel ratio of a value indicating a lean state is supplied to the PM removal filter 62 and the NOx purification catalyst 64 by the air supplied through the bypass passage 70. As a result, the PM deposited in the PM removal filter 62 is easily burned, and the NOx purification catalyst 64 promotes the purification of NOx.

For example, when the second throttle valve 72 is not in the valve open state, NOx is not sufficiently purified in the TWC 60 due to a decrease in oxygen storage amount, and NOx is also produced in the NOx purification catalyst 64 due to the rich air-fuel ratio. Not sufficiently purified. Therefore, as shown in LN8 of FIG. 9, the NOx emission amount increases after the time t (3), and then the state in which a certain amount of NOx is discharged continues.

On the other hand, when the second throttle valve 72 is opened at time t (3), the second throttle valve 72 is opened via the bypass passage 70. Since NOx is purified in the NOx purification catalyst 64 by the supplied air, as shown in LN9 of FIG. 9, the state in which NOx is not discharged continues even after the time t (3).

When the air-fuel ratio becomes lean (NO in S204) at time t (4), the second throttle valve 72 is in the open state (YES in S216), so that the valve is closed. The second throttle valve 72 is controlled (S218).

As described above, according to the engine system 1 according to the present embodiment, at least one of the condition that the oxygen storage amount is lower than the threshold value and the air-fuel ratio of the exhaust gas of the engine is in a stoichiometric state or a rich state. When a predetermined condition including the condition that the value indicates the state is satisfied, the second throttle valve 72 is opened in the state of being appropriately supercharged by the supercharger 50. Therefore, even if NOx cannot be sufficiently purified in the TWC 60 included in the upstream exhaust gas treatment device, air is supplied to the downstream exhaust gas treatment device via the bypass passage 70, so that the exhaust gas supplied to the NOx purification catalyst 64 is supplied. Since the air-fuel ratio can be changed to a value on the lean side, deterioration of NOx purification performance can be suppressed. Therefore, it is possible to provide an engine system that suppresses the deterioration of the exhaust gas purification performance of the exhaust gas treatment device while suppressing the operating state of the turbocharger from entering the surge region.

Further, the ECU 100 calculates the flow rate of the gas flowing through the bypass passage 70 using the pressure difference between the first pressure and the second pressure, and calculates the flow rate of the gas flowing through the engine 2 using the calculated flow rate. Can be calculated. Therefore, the fuel injection amount of the engine 2 can be appropriately adjusted, and the air-fuel ratio of the exhaust can be adjusted to an appropriate air-fuel ratio.

Further, since the check valve 74 is provided in the bypass passage 70, it is possible to suppress the backflow of gas from the exhaust side to the intake side via the bypass passage 70.

Further, since the TWC 60 is provided as an exhaust treatment device on the upstream side of the third exhaust passage 42 to which air is supplied from the bypass passage 70, the TWC 60 is excluded from the air supply target via the bypass passage 70. Therefore, it is possible to prevent the temperature of the TWC 60 from dropping unnecessarily.

Hereinafter, modification examples will be described.
In the above-described embodiment, the second throttle valve 72 has been described as switching from one of the valve open state and the valve closed state to the other state, but the second throttle valve 72 is described. , The opening degree may be configured to be adjustable. By doing so, for example, the opening degree of the second throttle valve 72 can be adjusted so that the flow rate of the gas flowing through the bypass passage 70 becomes the target flow rate. Therefore, the amount of air supplied to the exhaust treatment device on the downstream side of the third exhaust passage 42 can be adjusted to an appropriate amount. Therefore, it is possible to suppress deterioration of the exhaust purification performance of the exhaust gas treatment device on the downstream side.

Further, in the above-described embodiment, the flow rate calculation unit 104 has been described as calculating the flow rate of the air flowing through the bypass passage 70 from the pressure difference between the first pressure and the second pressure. If the opening degree can be adjusted, the flow rate of the air flowing through the bypass passage 70 may be calculated as follows. That is, a map showing the relationship between the first pressure, the opening degree of the second throttle valve 72, and the flow rate of the air flowing through the bypass passage 70 is created by an experiment or the like, and the flow rate calculation unit 104 uses the first pressure. And, the flow rate of the air flowing through the bypass passage 70 may be calculated from the opening degree of the second throttle valve 72 and the above map.

Further, in the above-described embodiment, the configuration in which the TWC 60 is provided as the exhaust treatment device on the upstream side of the third exhaust passage 42 to which the air from the bypass passage 70 is supplied has been described as an example, but the exhaust treatment on the upstream side has been described. The device is not particularly limited to the TWC60. The exhaust gas treatment device on the upstream side may include, for example, at least one of an oxidation catalyst (DOC), a PM removal filter, and a NOx purification catalyst instead of the TWC60.

Further, in the above-described embodiment, the case where the supercharger 50 is a turbocharger has been described as an example, but the supercharger 50 may be, for example, a supercharger or an electric turbocharger. good.

Further, in the above-described embodiment, the exhaust treatment device downstream from the position where the other end of the bypass passage 70 is connected includes the PM removal filter 62 and the NOx purification catalyst 64, but at least NOx purification is described. It suffices if the catalyst 64 is provided. For example, in addition to the NOx purification catalyst 64, at least one of the PM removal filter, the three-way catalyst, and the oxidation catalyst may be provided as the exhaust gas treatment device on the downstream side. good.

In addition, the above-mentioned modification may be carried out by combining all or a part thereof.
<Third embodiment>
In the first embodiment, when the predetermined condition that the operating point of the turbocharger 50 is within the predetermined range is satisfied, the valve is opened in the state of being supercharged by the turbocharger 50. The second throttle valve 72 was controlled so as to be. On the other hand, in the third embodiment, when the predetermined condition for the amount of PM accumulated in the PM removal filter 62 is satisfied, the ECU 100 is supercharged by the supercharger 50. It is assumed that the second throttle valve 72 is controlled so as to be in the valve open state.

FIG. 10 is a diagram showing an example of a schematic configuration of the engine system 1 according to the third embodiment. In the configuration of the engine system 1 according to the third embodiment shown in FIG. 10, the atmospheric pressure gauge 206 is omitted as compared with the configuration of the engine system 1 according to the first embodiment shown in FIG. Further, the ECU 100 further includes the PM deposit amount estimation unit 108, and the turbine 54 includes the variable nozzle mechanism 58. Other configurations are the same as the configuration of the engine system 1 shown in FIG. 1, and the same reference numerals are given. Therefore, the detailed description of their configuration will not be repeated. Further, since the variable nozzle mechanism 58 is the same as the variable nozzle mechanism 58 described in the second embodiment described above, the detailed description thereof will not be repeated.

The ECU 100 further includes a PM deposition amount estimation unit 108. The PM deposit estimation unit 108 estimates the PM deposit in the PM removal filter 62. The ECU 100 determines, for example, the amount of PM discharged from the engine 2 for a predetermined period (for example, a control cycle) from the operating conditions of the engine 2 (for example, the command value of the engine speed and the fuel injection amount, the intake air amount, etc.). Is calculated. The ECU 100 estimates the PM accumulation amount by integrating the PM emission amount for the calculated predetermined period. The ECU 100 may estimate the amount of PM deposited in the PM removal filter 62 by, for example, the pressure difference between the upstream and downstream of the PM removal filter 62. The PM deposit estimation unit 108 outputs the estimation result of the PM deposit to the engine control unit 102.

In such a configuration, in the present embodiment, the ECU 100 uses the turbocharger 50 when a predetermined condition including a condition that the PM accumulation amount in the PM removal filter 62 is equal to or more than the threshold value is satisfied. It is assumed that the second throttle valve 72 is controlled so as to be in the valve open state in the supercharged state.

In this way, when the predetermined execution conditions are satisfied and the second throttle valve 72 is opened, the exhaust treatment on the downstream side of the third exhaust passage 42 to which the other end of the bypass passage 70 is connected is established. Air is supplied to the PM removal filter 62, which is an apparatus, via the third exhaust passage. Therefore, the air-fuel ratio of the exhaust gas flowing through the PM removal filter 62 can be changed to the lean side. Therefore, the soot collected by the PM removal filter 62 can be burned to regenerate the PM removal filter 62.

Hereinafter, the process executed by the ECU 100 in the third embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing an example of the process executed by the ECU 100 in the third embodiment. The process shown in this flowchart is called from the main routine and executed every predetermined control cycle.

In S300, the ECU 100 acquires the first pressure. The ECU 100 acquires the first pressure by using the first pressure gauge 202.

In S302, the ECU 100 estimates the amount of PM deposited in the PM removal filter 62. Since the method for estimating the PM deposition amount is as described above, the detailed description thereof will not be repeated.

In S304, the ECU 100 determines whether or not the PM deposit amount is equal to or greater than the threshold value. The threshold value is, for example, a value for determining whether or not the regeneration process is necessary in the PM removal filter 62, and is fitted by an experiment or the like. If it is determined that the PM deposit is equal to or greater than the threshold value (YES in S304), the process is transferred to S306.

In S306, the ECU 100 executes the boost pressure increase control. The specific control method is the same as the boost pressure increase control shown in the process of S206 in the flowchart of FIG. 8 in the second embodiment described above. Therefore, the detailed explanation will not be repeated.

In S308, the ECU 100 controls the second throttle valve 72 so that the valve is opened. When the second throttle valve 72 is opened, the ECU 100 turns on a flag indicating that the second throttle valve 72 is in the opened state.

In S310, the ECU 100 acquires the first pressure and the second pressure. The ECU 100 acquires the first pressure by using the first pressure gauge 202 and acquires the second pressure by using the second pressure gauge 204. It is desirable that the ECU 100 acquires the first pressure and the second pressure after a predetermined time for the pressure change to converge after the second throttle valve 72 is opened.

In S312, the ECU 100 calculates the flow rate of air passing through the bypass passage 70. The ECU 100 calculates the flow rate of air passing through the bypass passage 70 using the pressure difference between the first pressure and the second pressure.

In S314, the ECU 100 controls the engine 2 so that the air-fuel ratio becomes the target air-fuel ratio. The specific control method is the same as the control method of the engine 2 shown in the process of S112 in the flowchart of FIG. 2 in the first embodiment described above. Therefore, the detailed explanation will not be repeated.

If the PM deposition amount is smaller than the threshold value (NO in S304), the treatment is transferred to S316.

In S316, the ECU 100 determines whether or not the second throttle valve 72 is in the valve open state. The ECU 100 determines that the second throttle valve 72 is in the open state, for example, when the flag indicating that the second throttle valve 72 is in the open state is on. When it is determined that the second throttle valve 72 is in the valve open state (YES in S316), the process is transferred to S318.

In S318, the ECU 100 controls the second throttle valve 72 so that the valve is closed. When the second throttle valve 72 is closed, the ECU 100 turns off the flag indicating that the second throttle valve 72 is in the open state.

When it is determined that the second throttle valve 72 is not in the valve open state (NO in S316), this process is terminated.

The operation of the ECU 100 based on the above structure and the flowchart will be described. It is assumed that the second throttle valve 72 is in a closed state.

As the first pressure is acquired (S300), the amount of PM deposited in the PM removal filter 62 is estimated (S302). It is determined whether or not the estimated PM deposit is equal to or greater than the threshold value (S304). When the PM deposit amount is smaller than the threshold value (NO in S304), the closed state of the second throttle valve 72 is maintained (NO in S316). As the operation of the engine 2 continues, the amount of PM deposited in the PM removal filter 62 increases with the passage of time.

When the PM deposit amount exceeds the threshold value (YES in S304), the variable nozzle mechanism 58 is controlled so that the first pressure exceeds the threshold value by executing the boost pressure increase control (S306). ), The second throttle valve 72 is opened (308). Then, when the first pressure and the second pressure are acquired (S310), the flow rate of the air flowing through the bypass passage 70 is calculated using the acquired pressure difference between the first pressure and the second pressure (S310). S312). The control of the engine 2 is executed using the calculated air flow rate (S314).

Exhaust gas having an air-fuel ratio of a value indicating a lean state is supplied to the PM removal filter 62 and the NOx purification catalyst 64 by the air supplied through the bypass passage 70. As a result, the PM accumulated in the PM removal filter 62 is burned to promote the regeneration of the PM removal filter 62 and promote the purification of NOx in the NOx purification catalyst 64.

If the PM deposit amount is smaller than the threshold value (NO in S304) and the second throttle valve 72 is in the valve open state (YES in S316), the second throttle valve is closed. The valve 72 is controlled (S318).

As described above, according to the engine system 1 according to the present embodiment, the turbocharger 50 is appropriate when a predetermined condition including a condition that the PM deposit amount becomes larger than the threshold value is satisfied. The second throttle valve 72 is opened in the state of being supercharged. Therefore, since air is supplied to the PM removal filter 62 via the bypass passage 70, the PM accumulated in the PM removal filter 62 can be burned to regenerate the PM removal filter 62. Therefore, it is possible to provide an engine system that suppresses the deterioration of the exhaust gas purification performance of the exhaust gas treatment device while suppressing the operating state of the turbocharger from entering the surge region.

Further, the ECU 100 calculates the flow rate of the gas flowing through the bypass passage 70 using the pressure difference between the first pressure and the second pressure, and calculates the flow rate of the gas flowing through the engine 2 using the calculated flow rate. Can be calculated. Therefore, the fuel injection amount of the engine 2 can be appropriately adjusted, and the air-fuel ratio of the exhaust can be adjusted to an appropriate air-fuel ratio.

Further, since the check valve 74 is provided in the bypass passage 70, it is possible to suppress the backflow of gas from the exhaust side to the intake side via the bypass passage 70.

Further, since the TWC 60 is provided as an exhaust treatment device on the upstream side of the third exhaust passage 42 to which air is supplied from the bypass passage 70, the TWC 60 is excluded from the air supply target via the bypass passage 70. Therefore, it is possible to prevent the temperature of the TWC 60 from dropping unnecessarily.

Hereinafter, modification examples will be described.
In the above-described embodiment, the second throttle valve 72 has been described as switching from one of the valve open state and the valve closed state to the other state, but the second throttle valve 72 is described. , The opening degree may be configured to be adjustable. By doing so, for example, the opening degree of the second throttle valve 72 can be adjusted so that the flow rate of the gas flowing through the bypass passage 70 becomes the target flow rate. Therefore, the amount of air supplied to the exhaust treatment device on the downstream side of the third exhaust passage 42 can be adjusted to an appropriate amount. Therefore, it is possible to suppress deterioration of the exhaust purification performance of the exhaust gas treatment device on the downstream side.

Further, in the above-described embodiment, the flow rate calculation unit 104 has been described as calculating the flow rate of the air flowing through the bypass passage 70 from the pressure difference between the first pressure and the second pressure. If the opening degree can be adjusted, the flow rate of the air flowing through the bypass passage 70 may be calculated as follows. That is, a map showing the relationship between the first pressure, the opening degree of the second throttle valve 72, and the flow rate of the air flowing through the bypass passage 70 is created by an experiment or the like, and the flow rate calculation unit 104 uses the first pressure. And, the flow rate of the air flowing through the bypass passage 70 may be calculated from the opening degree of the second throttle valve 72 and the above map.

Further, in the above-described embodiment, the configuration in which the TWC 60 is provided as the exhaust treatment device on the upstream side of the third exhaust passage 42 to which the air from the bypass passage 70 is supplied has been described as an example, but the exhaust treatment on the upstream side has been described. The device is not particularly limited to the TWC60. The exhaust gas treatment device on the upstream side may include, for example, at least one of an oxidation catalyst (DOC), a PM removal filter, and a NOx purification catalyst instead of the TWC60.

Further, in the above-described embodiment, the case where the supercharger 50 is a turbocharger has been described as an example, but the supercharger 50 may be, for example, a supercharger or an electric turbocharger. good.

Further, in the above-described embodiment, the exhaust gas treatment device downstream from the position where the other end of the bypass passage 70 is connected includes the PM removal filter 62 and the NOx purification catalyst 64, but at least PN removal. A filter 62 may be provided. For example, in addition to the PM removal filter 62, at least one of a NOx purification catalyst, a three-way catalyst, and an oxidation catalyst may be provided as an exhaust gas treatment device on the downstream side. good.

In addition, the above-mentioned modification may be carried out by combining all or a part thereof.
It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 engine system, 2 engine, 10 1st intake passage, 12 1st throttle valve, 20 2nd intake passage, 30 1st exhaust passage, 40 2nd exhaust passage, 42 3rd exhaust passage, 50 supercharger, 52 compressor , 54 turbine, 56 shaft, 58 variable nozzle mechanism, 60 three-way catalyst, 62 PM removal filter, 64 NOx purification catalyst, 70 bypass passage, 72 second throttle valve, 74 check valve, 80 EGR passage, 82 EGR valve, 100 ECU, 102 engine control unit, 104 flow rate calculation unit, 106 valve control unit, 108 PM accumulation amount estimation unit, 200 flow meter, 202 first pressure gauge, 204 second pressure gauge, 206 atmospheric pressure gauge, 208 air-fuel ratio gauge.

Claims (13)

With the engine
A turbocharger including a compressor provided in the intake passage of the engine and supercharging the intake air sucked into the engine by using the compressor.
A plurality of exhaust treatment devices provided in the exhaust passage of the engine to purify the exhaust gas discharged from the engine, and
A first throttle valve provided between the compressor and the engine and configured to be able to adjust the amount of air flowing through the intake passage.
One end is connected to a position in the intake passage between the compressor and the first throttle valve, and the other end is located in the exhaust passage between two of the plurality of exhaust treatment devices. Bypass passage to be connected and
A second throttle valve configured to be able to adjust the amount of air flowing through the bypass passage,
A control device for controlling the operation of the second throttle valve is provided.
The control device is an engine system that controls the second throttle valve so that the valve is opened in a state of being supercharged by the supercharger when a predetermined condition is satisfied. The predetermined condition is that the operating region of the turbocharger, which is indicated by the pressure ratio and the intake air amount in the compressor, is adjacent to the boundary between the surge region of the turbocharger and the intake air amount side of the surge region. The engine system according to claim 1, wherein the engine system includes the condition that the first region is included in the engine system. In the control device, the operating region indicated by the pressure ratio calculated by using the first pressure and the atmospheric pressure of the air flowing out from the compressor and the intake air amount flowing into the compressor is the first. The engine system according to claim 2, wherein the operation with the second throttle valve is controlled so as to be within a predetermined second region including the region. The upstream exhaust treatment device on the upstream side of the circulating exhaust gas among the two exhaust gas treatment devices includes at least one of a three-way catalyst, an oxidation catalyst, a PM removal filter, and a NOx purification catalyst. The engine system according to any one of claims 1 to 3. Of the two exhaust treatment devices, the upstream side exhaust treatment device on the upstream side of the circulating exhaust gas includes a three-way catalyst.
The downstream exhaust gas treatment device on the downstream side of the circulating exhaust gas among the two exhaust gas treatment devices includes at least one of a three-way catalyst, an oxidation catalyst, and a NOx purification catalyst.
The predetermined conditions are that the oxygen storage amount in the upstream exhaust treatment device is lower than the threshold value and that the air-fuel ratio of the exhaust of the engine is at least one of a stoichiometric state and a rich state. The engine system according to claim 1, comprising the condition that the value indicates. Of the two exhaust treatment devices, the upstream side exhaust treatment device on the upstream side of the circulating exhaust gas includes a three-way catalyst.
The engine system according to claim 1, wherein the downstream exhaust gas treatment device on the downstream side of the circulating exhaust gas of the two exhaust gas treatment devices includes a PM removal filter and a NOx purification catalyst. The engine system according to claim 5 or 6, wherein the NOx purification catalyst comprises at least one of a selective reduction type NOx purification catalyst and a storage reduction type NOx purification catalyst. The downstream exhaust treatment device on the downstream side of the circulating exhaust of the two exhaust treatment devices includes a PM removal filter.
The engine system according to claim 1, wherein the predetermined condition includes a condition that the amount of PM deposited in the PM removal filter is larger than the threshold value. The turbocharger includes an adjusting device capable of adjusting the supercharging pressure.
When the predetermined conditions are satisfied, the control device controls the adjusting device so that the boost pressure becomes higher than the threshold value, and opens the second throttle valve. The engine system according to any one of claims 5 to 8. The control device calculates the flow rate of the gas flowing through the bypass passage, and calculates the flow rate of the gas flowing through the engine using the calculated flow rate, according to any one of claims 1 to 9. The engine system described. The control device calculates the flow rate of the gas flowing through the bypass passage, and adjusts the opening degree of the second throttle valve so that the calculated flow rate becomes the target flow rate, according to any one of claims 1 to 10. The engine system described in. The engine system is
A first pressure detecting device for detecting the first pressure of the gas flowing between the compressor and the first throttle valve in the intake passage, and a first pressure detecting device.
A second pressure detecting device for detecting the second pressure of the gas in the bypass passage is further provided.
The engine system according to claim 10 or 11, wherein the control device calculates the flow rate of gas flowing through the bypass passage by using the difference between the first pressure and the second pressure. The engine system according to any one of claims 1 to 12, further comprising a valve provided in the bypass passage and suppressing a backflow of gas from the other end to the one end in the bypass passage.

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