JP2023016352A - Exhaust emission control system - Google Patents

Abstract

To provide an exhaust emission control system capable of regenerating a particulate matter collection function without generating white smoke in exhaust gas in an internal combustion engine having turbochargers provided in parallel.SOLUTION: An emission control catalyst device is disposed in an exhaust gas passage of an internal combustion engine in which a main turbocharger and an auxiliary turbocharger are provided in parallel. In the emission control catalyst device, a temperature of exhaust gas is raised by oxidizing unburned fuel added to exhaust gas from a fuel addition valve disposed upstream of the emission control catalyst device so as to regenerate a particulate matter collection function. On the basis of an inlet side exhaust gas temperature detected via a first exhaust temperature detection device disposed upstream of the emission control catalyst device, an exhaust gas flow rate acquired via an exhaust gas flow rate acquisition device and a supercharging state obtained by the main turbocharger and the auxiliary turbocharger, a fuel limitation addition amount is calculated as an upper limit value of addition amount per unit time of the unburned fuel added to exhaust gas from the fuel addition valve.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust purification system that purifies exhaust gas discharged from an engine.

An exhaust purification system for a diesel engine is a particulate matter removal filter (usually called a Diesel Particulate Filter, hereinafter referred to as "DPF") that collects and removes particulate matter (PM) in exhaust gas. ) and selective reduction catalyst with filter (hereinafter referred to as “SCR-DPF”). Here, since the DPF and SCR-DPF are for collecting particulate matter in the exhaust gas, the DPF and SCR-DPF must be removed before exhaust resistance increases due to clogging due to accumulation of particulate matter (PM). -Various proposals have been made regarding techniques for regenerating the trapping function by burning and incinerating particulate matter in the DPF.

For example, in the exhaust purification device described in Patent Document 1 below, an oxidizing device that oxidizes and purifies HC (hydrocarbon) and CO (carbon monoxide) contained in the exhaust gas is provided in the exhaust passage on the downstream side of the turbocharger. A catalytic converter and a DPF for trapping particulate matter (PM) are arranged in sequence. A first exhaust gas temperature sensor is arranged in the exhaust passage on the upstream side of the oxidation catalytic converter. A second exhaust temperature sensor is arranged in the exhaust passage between the oxidation catalytic converter and the DPF. Furthermore, a differential pressure sensor is provided to detect the differential pressure between the upstream side pressure and the downstream side pressure of the DPF.

Then, the ECU estimates the amount of PM accumulated in the DPF based on the output signal of the differential pressure sensor, and executes filter regeneration processing to regenerate the DPF when the amount reaches a predetermined amount. Specifically, from the exhaust gas flow rate estimated based on the output signal of the air flow meter and the temperature of the oxidation catalytic converter (catalyst bed temperature) estimated from the exhaust gas temperature detected by the second exhaust temperature sensor, Find the total fuel supply that does not cause white smoke in the exhaust gas. Then, the amount of fuel to be injected into the combustion chamber is subtracted from the total fuel supply amount to calculate the "A/F limited addition amount" that does not cause white smoke in the exhaust gas that can be supplied from the fuel addition valve.

Further, from the exhaust gas flow rate estimated based on the output signal of the air flow meter and the oxidation catalyst converter temperature (catalyst bed temperature) estimated from the exhaust gas temperature detected by the second exhaust temperature sensor, the oxidation catalyst converter Calculate the "required addition amount" to raise the temperature of the catalyst bed temperature to the target catalyst bed temperature. Then, the smaller of the "required addition amount" and the "A/F restricted addition amount" is integrated to calculate the effective standby fuel addition amount. After that, when the effective standby fuel addition amount reaches the reference addition amount, the reference addition amount is added (injected) from the addition valve toward the oxidation catalyst converter at the fuel addition timing.

JP 2011-231645 A

However, in an internal combustion engine equipped with turbochargers in parallel, the exhaust gas flows into the oxidation catalytic converter from the main turbine and the secondary turbine. (i.e., the mixed state of added fuel and exhaust gas, etc.) changes from moment to moment depending on the operating conditions. Further, the exhaust gas temperature detected by the second exhaust temperature sensor is the temperature of the exhaust gas that has been raised by oxidizing the unburned fuel, so the accuracy of estimating the catalyst bed temperature of the oxidation catalytic converter is low. Therefore, when the fuel addition amount is determined based on the state quantity (exhaust gas temperature, exhaust gas flow rate, etc.) on the outlet side of the oxidation catalytic converter, white smoke (unburned fuel) is generated in the exhaust gas. There is fear.

Therefore, the present invention has been invented in view of such points, and has a function of collecting particulate matter without generating white smoke in the exhaust gas in an internal combustion engine equipped with a turbocharger in parallel. An object of the present invention is to provide an exhaust purification system that can be regenerated.

In order to solve the above problems, a first aspect of the present invention provides an internal combustion engine having a main turbocharger and a sub-turbocharger connected in parallel to the main turbocharger, and an exhaust gas of the internal combustion engine. A purification catalyst device disposed in a passage to oxidize unburned fuel in the exhaust gas to raise the temperature of the exhaust gas and regenerate a particulate matter trapping function; and the purification catalyst device in the exhaust gas passage. a fuel addition valve for adding the unburned fuel to the exhaust gas; and an inlet side exhaust gas flowing into the purification catalyst device disposed upstream of the purification catalyst device in the exhaust gas passage. a first exhaust temperature detection device that detects gas temperature; an exhaust gas flow rate acquisition device that acquires an exhaust gas flow rate; a supercharging state acquisition device that acquires a supercharging state by the main turbocharger and the sub turbocharger; The inlet-side exhaust gas temperature detected via the first exhaust temperature detection device, the exhaust gas flow rate obtained via the exhaust gas flow rate obtaining device, and the supercharging obtained via the supercharging state obtaining device and a limit addition amount calculation device for calculating a limit addition amount of fuel as an upper limit value of the addition amount per unit time of the unburned fuel added to the exhaust gas from the fuel addition valve, based on the condition. , is an exhaust purification system.

Next, according to a second aspect of the present invention, in the exhaust purification system according to the first aspect, the supercharging state includes a single turbo mode in which only the main turbocharger is operated for supercharging; a twin-turbo mode in which the charger and the sub-turbocharger are operated for supercharging, and the limit addition amount calculation device is provided corresponding to the single turbo mode, and the limit addition amount of fuel is the exhaust gas. A single-turbo mode map set to decrease as the gas flow rate increases and increase as the inlet-side exhaust gas temperature increases; a twin-turbo mode map that is set to decrease as the exhaust gas flow rate increases and to increase as the inlet side exhaust gas temperature increases; When the supercharging state acquired via the device is the single turbo mode, the inlet side exhaust gas temperature detected via the first exhaust temperature detection device and the exhaust gas flow rate acquisition device The obtained exhaust gas flow rate is compared with the map for single turbo mode to calculate the limited addition amount of fuel, and the supercharging state obtained through the supercharging state obtaining device is used in the twin turbo mode. In the case of, the inlet side exhaust gas temperature detected via the first exhaust temperature detection device and the exhaust gas flow rate obtained via the exhaust gas flow rate obtaining device are stored in the twin turbo mode map. It is an exhaust gas purification system that compares and calculates the limited fuel addition amount.

Next, according to a third invention of the present invention, in the exhaust purification system according to the first invention or the second invention, the purification catalyst device carries a noble metal that oxidizes the unburned fuel in the exhaust gas. an oxidation catalyst; a filter-equipped selective reduction catalyst arranged downstream of the oxidation catalyst for collecting particulate matter and selectively purifying NOx in the exhaust gas with a reducing agent solution having a predetermined concentration; a reducing agent addition valve arranged downstream of the oxidation catalyst and upstream of the filter-equipped selective reduction catalyst for adding the reducing agent solution to the exhaust gas; a deposition amount acquiring device for acquiring the deposition amount of the particulate matter collected by the catalyst; and determining whether or not the deposition amount of the particulate matter acquired via the deposition amount acquisition device has reached a predetermined deposition amount. and when it is determined by the deposition amount determination device that the deposition amount of the particulate matter has reached a predetermined deposition amount, the remaining amount of the particulate matter is added to the exhaust gas through the fuel addition valve. an exhaust purification system comprising a reducing agent addition stop setting device that sets so as to add fuel at a predetermined timing and sets so that the reducing agent solution is not added to the exhaust gas from the reducing agent addition valve. be.

Next, according to a fourth invention of the present invention, in the exhaust purification system according to any one of the first to third inventions, one end of the main turbocharger is connected to the outlet side of the main turbine of the main turbocharger. a first exhaust pipe for guiding exhaust gas to the inlet side of the purification catalyst device; one end connected to the outlet side of the sub-turbine of the sub-turbocharger; and the other end connected to the first exhaust pipe, a second exhaust pipe that guides exhaust gas to the inlet side of the purification catalyst device, wherein the fuel addition valve and the first exhaust gas temperature detection device are arranged in the first exhaust pipe. is.

According to the first invention, the purification catalyst device is arranged in an exhaust gas passage of an internal combustion engine having a main turbocharger and a sub-turbocharger in parallel. The purification catalyst device oxidizes the unburned fuel added to the exhaust gas from the fuel addition valve arranged upstream of the purification catalyst device, thereby raising the temperature of the exhaust gas and regenerating the particulate matter collection function. be done. Also, the temperature of the inlet-side exhaust gas flowing into the purification catalyst device is detected via the first exhaust gas temperature detection device arranged upstream of the purification catalyst device. Then, based on the inlet side exhaust gas temperature, the exhaust gas flow rate acquired via the exhaust gas flow rate acquisition device, and the supercharging state by the main turbocharger and the sub-turbocharger, fuel is added to the exhaust gas from the fuel addition valve. A fuel limit addition amount is calculated as an upper limit value of the addition amount of unburned fuel per unit time.

As a result, the amount of unburned fuel added to the exhaust gas from the fuel addition valve per unit time is made equal to or less than the fuel limit addition amount, thereby reducing the total amount of unburned fuel added to the exhaust gas from the fuel addition valve. It is possible to raise the temperature of the exhaust gas by oxidizing it with the purification catalyst device. As a result, in an internal combustion engine having a main turbocharger and a sub-turbocharger in parallel, the particulate matter trapping function can be regenerated without producing white smoke in the exhaust gas.

According to the second invention, when the supercharging state is the single turbo mode in which only the main turbocharger is operated for supercharging, the limited addition amount calculating device calculates the inlet side exhaust gas temperature and the exhaust gas flow rate. The fuel limit addition amount is calculated by referring to the map for single turbo mode. In addition, when the supercharging state is the twin-turbo mode in which the main turbocharger and the sub-turbocharger are operated for supercharging, the limited addition amount calculation device calculates the inlet-side exhaust gas temperature and the exhaust gas flow rate in the twin-turbo mode. The fuel limit addition amount is calculated by referring to the map for use. As a result, the limited fuel addition amount can be quickly set according to the operation states of the main turbocharger and the sub-turbocharger when the supercharging state is the single turbo mode and when the supercharging state is the twin turbo mode. be able to.

According to the third invention, when the accumulated amount of particulate matter collected by the selective reduction catalyst with filter (SCR-DPF) reaches the predetermined accumulated amount, the amount of accumulated particulate matter is reduced to the exhaust gas through the fuel addition valve. The setting is made such that the fuel is added at a predetermined timing, and the reducing agent addition valve is set so as not to add the reducing agent solution to the exhaust gas. As a result, the particulate matter collection function of the filter-equipped selective reduction catalyst (SCR-DPF) is regenerated, and a decrease in the catalyst bed temperature of the filter-equipped selective reduction catalyst due to the reducing agent solution is suppressed, resulting in a collection function. It is possible to shorten the playback time of

According to the fourth aspect of the invention, the fuel addition valve and the first exhaust gas temperature detection device have one end connected to the outlet side of the main turbine of the main turbocharger, and guide the exhaust gas to the inlet side of the purification catalyst device. located in the exhaust pipe. As a result, in the case of the single turbo mode in which only the main turbocharger is operated for supercharging, and in the case of the twin turbo mode in which the main turbocharger and the sub turbocharger are operated for supercharging, Unburned fuel can be added to the exhaust gas from the fuel addition valve, and the inlet-side exhaust gas temperature can be detected.

Therefore, in both the single-turbo mode and the twin-turbo mode, by making the amount of unburned fuel added to the exhaust gas from the fuel addition valve per unit time equal to or less than the fuel limit addition amount, The entire amount of unburned fuel added to the exhaust gas from the fuel addition valve can be oxidized by the purification catalyst device to raise the temperature of the exhaust gas. As a result, in an internal combustion engine having a main turbocharger and a sub-turbocharger in parallel, the particulate matter trapping function can be regenerated without producing white smoke in the exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining an example of a schematic structure of the exhaust gas purification system which concerns on this embodiment. FIG. 4 is a diagram showing an example of an operating region map that determines operating regions in single turbo mode and twin turbo mode; FIG. 5 is a diagram showing an example of a supercharging mode setting map that determines the setting states of an exhaust switching valve, an intake switching valve, and an intake bypass valve in each supercharging mode; 4 is a main flowchart showing an example of filter regeneration processing for regenerating an SCR-DPF, which is executed by the control device according to the present embodiment; FIG. 5 is a sub-flowchart showing a sub-process of a "PM deposition state acquisition process" shown in FIG. 4; FIG. FIG. 5 is a sub-flowchart showing a sub-process of a "fuel addition amount acquisition process" shown in FIG. 4; FIG. FIG. 5 is a sub-flowchart showing sub-processing of "PM counter update processing" shown in FIG. 4; FIG. FIG. 5 is an explanatory diagram showing an example of the concentration of HC discharged from the tail pipe with respect to the amount of added fuel when the temperature of the exhaust gas on the inlet side of the oxidation catalyst is constant and the flow rate of the exhaust gas is changed. FIG. 5 is an explanatory diagram showing an example of the concentration of HC discharged from the tail pipe with respect to the fuel addition amount when the exhaust gas flow rate is constant and the exhaust gas temperature on the inlet side of the oxidation catalyst is changed. FIG. 10 is a diagram showing an example of a map for determining a limited fuel addition amount in single turbo mode; FIG. FIG. 10 is a diagram showing an example of a map for determining a restricted fuel addition amount in twin-turbo mode; FIG. FIG. 4 is a diagram showing an example of the relationship between the catalyst bed temperature of the SCR-DPF and the PM burning rate; FIG. 11 is a sub-flowchart showing a sub-process of a “second fuel addition amount acquisition process” according to another first embodiment; FIG. FIG. 10 is a diagram showing an example of a map for obtaining a restricted fuel addition amount in a twin switching mode; FIG. FIG. 10 is a diagram showing an example of a map for determining a limited fuel addition amount in single switching mode; FIG. 11 is a sub-flowchart showing sub-processing of “third fuel addition amount acquisition processing” according to another second embodiment; FIG. FIG. 11 is a diagram illustrating an example of the configuration of an exhaust gas purification system according to another third embodiment; FIG. 11 is a diagram illustrating an example of the configuration of an exhaust gas purification system according to another fourth embodiment; FIG. 11 is a diagram illustrating an example of the configuration of an exhaust gas purification system according to another fifth embodiment;

DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description will be given below with reference to the drawings based on an embodiment of an exhaust purification system according to the present invention. First, a schematic configuration of an exhaust purification system 1 according to the present invention will be described with reference to FIG. FIG. 1 shows a schematic configuration of an exhaust purification system 1 according to the present invention.

As shown in FIG. 1, an exhaust purification system 1 according to the present embodiment includes an air cleaner 5, an intake flow rate detection device 6, an engine (for example, a diesel engine) 10 (internal combustion engine) mounted on a vehicle, a main turbo It is composed of a charger 21, a sub-turbocharger 22, an exhaust gas purification device 61 (purification catalyst device), an ECU 80, and the like. The engine 10 is a multi-cylinder engine having a left bank 10L and a right bank 10R. A main turbocharger 21 is provided in the left bank 10L and a sub-turbocharger 22 is provided in the right bank 10R.

Further, the left bank 10L is provided with a fuel injection device 15L capable of directly injecting fuel into each cylinder via a fuel injection valve (not shown) according to a control signal from the ECU 80. FIG. The right bank 10R is provided with a fuel injection device 15R capable of directly injecting fuel into each cylinder via a fuel injection valve (not shown) in response to a control signal from the ECU 80. FIG. Each member and the like will be described below while describing an intake path to the engine 10 and an exhaust path from the engine 10 .

The air cleaner 5 purifies air (intake air) obtained from the outside and supplies the air to the intake pipe 3 . The intake pipe 3 is branched into intake pipes 31L and 31R on the way. Further, an intake flow rate detection device (for example, an airflow meter) 6 for detecting the intake flow rate supplied to the intake pipe 3 before the intake pipe 3 is branched from the air cleaner 5 is arranged downstream of the air cleaner 5. It is

The downstream side of the intake pipe 31L is connected to the intake port of the main compressor 21B of the main turbocharger 21 . A discharge port of the main compressor 21B is connected to the upstream side of the intake pipe 32L. Further, the downstream side of the intake pipe 31R is connected to the intake port of the sub-compressor 22B of the sub-turbocharger 22. As shown in FIG. A discharge port of the sub-compressor 22B is connected to the upstream side of the intake pipe 32R. The downstream sides of the intake pipes 32L and 32R are connected to the upstream side of the intake pipe 33 . In the vicinity of the discharge port of the main compressor 21B of the intake pipe 32L, there is an intake air temperature detection device (for example, a temperature detection sensor) 27 for detecting the temperature of the intake air on the outlet side of the main compressor 21B, that is, the temperature at the outlet of the main compressor 21B. is provided.

The downstream side of the intake pipe 33 is connected to the upstream side of the intake manifold 34 . The intake manifold 34 supplies intake air to each cylinder of the right bank 10R and each cylinder of the left bank 10L of the engine 10, respectively. An intercooler 38 is arranged between the intake pipe 33 and the intake manifold 34 to cool the supercharged intake air. Further, an electronic throttle valve 39 capable of adjusting the amount of intake air introduced to the intake manifold 34 is arranged downstream of the intercooler 38 between the intake pipe 33 and the intake manifold 34 . The rotational position of the electronic throttle valve 39 is continuously driven and controlled from the fully closed position to the fully opened position by a control signal from the ECU 80 .

The main compressor 21B is rotationally driven by the main turbine 21A that is rotationally driven by the exhaust gas, compresses the air sucked from the intake pipe 31L, and passes through the intake pipes 32L and 33, the intercooler 38, and the electronic throttle valve 39. Then, it is discharged to the intake manifold 34 . An intake switching valve 51 for opening and closing the intake pipe 32R is provided in the intake pipe 32R whose upstream side is connected to the discharge port of the sub-compressor 22B. The intake switching valve 51 is driven by, for example, a diaphragm actuator, and is opened and closed by a control signal from the ECU 80 .

One end of the intake bypass pipe 36 is connected to the intake pipe 32R between the discharge port of the auxiliary compressor 22B and the intake switching valve 51, that is, upstream of the intake switching valve 51, and the other end is connected to the intake pipe 32R. , is connected upstream of the intake port of the main compressor 21B of the intake pipe 31L. That is, the intake bypass pipe 36 bypasses the downstream side of the discharge port of the sub-compressor 22B and the upstream side of the intake port of the main compressor 21B. An intake bypass valve 52 (bypass solenoid valve) for opening and closing the intake bypass pipe 36 is provided between both ends of the intake bypass pipe 36 . The intake bypass valve 52 is driven by, for example, a solenoid type electromagnetic actuator, and is opened and closed by a control signal from the ECU 80 .

Therefore, when the intake switching valve 51 opens the intake pipe 32R and the intake bypass valve 52 closes the intake bypass pipe 36, the auxiliary compressor 22B is rotated by the auxiliary turbine 22A which is rotationally driven by the exhaust gas. It is driven, compresses the air sucked from the intake pipe 31R, and discharges it to the intake manifold 34 via the intake pipes 32R and 33, the intercooler 38, and the electronic throttle valve 39. Further, a supercharging pressure sensor 55 for detecting the supercharging pressure P5 of the intake air supplied to the intake manifold 34 is provided downstream of the electronic throttle valve 39 . A pressure sensor 23 for detecting the outlet pressure P2 of the sub-compressor 22B is provided at a position downstream of the discharge port of the sub-compressor 22B.

On the other hand, when the intake switching valve 51 closes the intake pipe 32R and the intake bypass valve 52 opens the intake bypass pipe 36, the auxiliary compressor 22B is rotated by the auxiliary turbine 22A that is rotationally driven by the exhaust gas. It is driven, compresses the air taken in from the intake pipe 31R, passes through the intake pipe 32R and the intake bypass pipe 36, and discharges it into the intake pipe 31L connected to the intake port of the main compressor 21B. In other words, intake air cannot be supplied from the auxiliary compressor 22B to the intake manifold 34 via the intake pipes 32R and 33.

An exhaust manifold 41L is connected to the exhaust side of the left bank 10L of the engine 10, and an exhaust manifold 41R is connected to the exhaust side of the right bank 10R. The upstream side of the exhaust pipe 42L is connected to the downstream side of the exhaust manifold 41L. The upstream side of an upstream main exhaust pipe 43L connected to the inlet (inlet side) of the main turbine 21A of the main turbocharger 21 is connected to the downstream side of the exhaust pipe 42L.

Further, the upstream side of the exhaust pipe 42R is connected to the downstream side of the exhaust manifold 41R. The upstream side of the upstream side sub-exhaust pipe 43R connected to the inlet (inlet side) of the sub-turbine 22A of the sub-turbocharger 22 is connected to the downstream side of the exhaust pipe 42R. One end of the communication pipe 45 is connected to the downstream side of the exhaust pipe 42L, and the other end thereof is connected to the downstream side of the exhaust pipe 42R. That is, the exhaust pipe 42L and the exhaust pipe 42R are communicated by the communication pipe 45. As shown in FIG.

Further, the engine 10 is provided with an engine speed detection device 28 and the like. The engine rotation speed detection device 28 is, for example, a rotation angle sensor capable of detecting the rotation speed of the crankshaft of the engine 10 (engine rotation speed), the rotation angle of the crankshaft (for example, the compression top dead center timing of each cylinder), and the like. is. The ECU 80 can detect the rotation speed, rotation angle, etc. of the crankshaft of the engine 10 based on the detection signal from the engine rotation speed detection device 28 .

The main turbine 21A is rotationally driven by the exhaust gas flowing in from the upstream main exhaust pipe 43L, and rotationally drives the directly connected main compressor 21B. The sub-turbine 22A is rotationally driven by the exhaust gas flowing in from the upstream side sub-exhaust pipe 43R, and rotationally drives the directly connected sub-compressor 22B. Therefore, the sub-turbocharger 22 is connected in parallel with the main turbocharger 21 .

Further, an exhaust switching valve 53 for opening and closing the upstream side sub-exhaust pipe 43R is provided in the upstream side sub-exhaust pipe 43R. The exhaust switching valve 53 is driven by, for example, a diaphragm actuator, and is opened and closed by a control signal from the ECU 80 . As a result, both the intake switching valve 51 and the exhaust switching valve 53 are opened, and when the intake bypass valve 52 is closed, the exhaust gas flows into the main turbine 21A and the auxiliary turbine 22A. As a result, the main turbocharger 21 and the sub-turbocharger 22 are activated, and the intake air is supercharged by the main compressor 21B and the sub-compressor 22B (hereinafter sometimes referred to as "twin turbo mode").

On the other hand, when the intake switching valve 51, the exhaust switching valve 53, and the intake bypass valve 52 are all closed, the exhaust gas flows into the main turbine 21A, but is prevented from flowing into the sub-turbine 22A. As a result, the main turbocharger 21 operates and the intake air is supercharged by the main compressor 21B, but the sub-turbocharger 22 does not operate and the intake air is not supercharged by the sub-compressor 22B (hereinafter referred to as "single turbocharger"). (Sometimes referred to as "turbo mode".) That is, the intake switching valve 51, the intake bypass valve 52, and the exhaust switching valve 53 are interlocked to switch between opening and closing. In FIG. 1, dotted arrows indicate the flow of intake air and exhaust gas when both the intake switching valve 51 and the exhaust switching valve 53 are open and the intake bypass valve 52 is closed.

Further, the main turbine 21A is provided with a main variable nozzle mechanism 57 that controls the flow velocity of the exhaust gas to the main turbine 21A. The main variable nozzle mechanism 57 includes a plurality of variable nozzles (VN: Variable Nozzles) 57A, an actuator 57B, and a nozzle opening sensor 57C. A plurality of variable nozzles 57A are arranged in an exhaust inflow portion around the rotation axis of the turbine wheel, and guide the exhaust gas flowing in from the upstream main exhaust pipe 43L to the turbine wheel.

The actuator 57B rotates each of the plurality of variable nozzles 57A to adjust the gap between adjacent variable nozzles 57A (in the following description, this gap is referred to as "nozzle opening"). The actuator 57B is composed of, for example, a stamping motor or the like, and adjusts the nozzle opening of the variable nozzle 57A according to a control signal from the ECU 80. By closing the variable nozzle 57A (increasing the nozzle opening), the intake supercharging pressure P increases, and by opening the variable nozzle 57A (decreasing the nozzle opening), the intake supercharging pressure P decreases. do. Also, the nozzle opening sensor 57C detects the nozzle opening of the variable nozzle 57A and outputs a detection signal to the ECU 80 .

Further, the sub-turbine 22A is provided with a sub-variable nozzle mechanism 58 that controls the flow velocity of the exhaust gas to the sub-turbine 22A. The secondary variable nozzle mechanism 58 includes a plurality of variable nozzles (VN: Variable Nozzles) 58A, an actuator 58B, and a nozzle opening sensor 58C. The multiple variable nozzles 58A have substantially the same configuration as the multiple variable nozzles 57A that constitute the main variable nozzle mechanism 57 described above. The actuator 58B and the nozzle opening sensor 58C also have substantially the same configuration as the actuator 57B and the nozzle opening sensor 57C that constitute the main variable nozzle mechanism 57 described above.

Accordingly, the plurality of variable nozzles 58A have their nozzle openings adjusted by driving the actuator 58B, thereby changing the flow velocity of the exhaust gas flowing into the sub-turbine 22A. Accordingly, by closing the variable nozzle 58A (increasing the nozzle opening), the intake supercharging pressure P rises, and by opening the variable nozzle 58A (decreasing the nozzle opening), the intake supercharging pressure P decreases.

The upstream side of the first exhaust pipe 46L (exhaust gas passage) is connected to the discharge port (outlet side) of the main turbine 21A. Further, the upstream side of the second exhaust pipe 46R (exhaust gas passage) is connected to the discharge port (outlet side) of the auxiliary turbine 22A. The downstream side of the first exhaust pipe 46</b>L and the downstream side of the second exhaust pipe 46</b>R are connected and connected to an inflow port (inlet side) of the exhaust gas purification device 61 . Further, downstream of the first exhaust pipe 46L, a first exhaust temperature detection device (for example, a temperature detection sensor) 25 for detecting the temperature of the inlet-side exhaust gas discharged from the main turbine 21A and flowing into the exhaust gas purification device 61. is provided. The first exhaust temperature detection device 25 outputs a detection signal corresponding to the temperature of the exhaust gas flowing into the exhaust gas purification device 61 to the ECU 80 .

A fuel addition valve 29 is arranged in the first exhaust pipe 46L at a position downstream of the first exhaust gas temperature detection device 25 and upstream of the exhaust gas purification device 61 . This fuel addition valve 29 is provided so as to be able to directly add (inject) fuel into the exhaust gas in the first exhaust pipe 46L in response to a control signal from the ECU 80. As shown in FIG. Further, the second exhaust pipe 46R is provided with a second exhaust temperature detection device (for example, a temperature detection sensor) 26 for detecting the temperature of the inlet-side exhaust gas discharged from the auxiliary turbine 22A and flowing into the exhaust gas purification device 61. ing.

Inside the exhaust gas purification device 61, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 62 and an SCR-DPF 63 (filtered selective reduction catalyst) are provided from the upstream side. Further, the exhaust gas purification device 61 is provided with an intermediate exhaust gas temperature detection device 66 and a urea water addition valve 68 on the downstream side of the oxidation catalyst 62 and the upstream side of the SCR-DPF 63 . The upstream side of the exhaust pipe 47 is connected to the downstream side (outlet side) of the SCR-DPF 63 in the exhaust gas purification device 61 .

A downstream exhaust temperature detector 67 and a NOx sensor 69 are provided upstream of the exhaust pipe 47 . Further, in the exhaust gas purification device 61, the exhaust pressure downstream of the oxidation catalyst (DOC) 62 and upstream of the SCR-DPF 63 (equivalent to the exhaust pipe internal pressure) and the exhaust pipe internal pressure downstream of the SCR-DPF 63 , and a differential pressure sensor 65 for detecting a differential pressure (pressure difference).

The differential pressure sensor 65 detects the difference between the exhaust pressure (equivalent to the exhaust pipe internal pressure) downstream of the oxidation catalyst (DOC) 62 and upstream of the SCR-DPF 63 and the exhaust pipe internal pressure downstream of the SCR-DPF 63. A detection signal corresponding to the pressure (pressure difference) is output to the ECU 80 . The intermediate exhaust temperature detection device 66 and the downstream exhaust temperature detection device 67 output detection signals corresponding to the exhaust gas temperature to the ECU 80 . During normal operation of the engine 10, the urea solution addition valve 68 releases urea into the exhaust gas toward the SCR-DPF 63 every predetermined time (for example, 200 milliseconds to 400 milliseconds) according to a control signal from the ECU 80. Water (reducing agent solution) is added (sprayed). The NOx sensor 69 outputs a detection signal to the ECU 80 according to the NOx concentration in the exhaust gas.

The exhaust gas purification device 61 constitutes an exhaust gas passage, and removes harmful substances contained in the exhaust gas while the exhaust gas passes from the upstream side to the downstream side. Here, although the engine 10 is highly efficient and excellent in durability, it emits harmful substances such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). , is discharged together with the exhaust gas.

The oxidation catalyst (DOC) 62 consists of a cell-shaped cylindrical body made of ceramic, which is formed in a columnar shape or the like. ing. Then, the oxidation catalyst (DOC) 62 passes the exhaust gas through a number of through-holes at a predetermined temperature (for example, about 200 [° C.] to 400 [° C.]) to reduce carbon monoxide ( CO), hydrocarbons (HC), etc. are removed by oxidation.

The SCR-DPF63 is an integrated DPF and a selective catalytic reduction (SCR). Specifically, the SCR-DPF 63 is formed in a columnar shape or the like from a porous member made of a ceramic material or the like, and has a honeycomb-structured cellular cylindrical body with a large number of small holes provided in the axial direction. The holes are closed by plugging members at different ends alternately between adjacent holes. In the SCR-DPF 63, an SCR layer of titania/vanadium catalyst (V ₂ O ₅ /WO ₃ /TiO ₂ ) or the like is formed on the surface of each small hole of the honeycomb structure by wash coating or the like. .

The SCR-DPF 63 configured in this way collects particulate matter (PM) in each small hole of the honeycomb structure by allowing the exhaust gas flowing into each small hole from the upstream side to pass through the porous material. Only the gas is allowed to flow downstream through the adjacent small hole. In addition, the SCR-DPF 63 is supplied with urea water (reducing agent solution) of a predetermined concentration (for example, urea 32 .5%, pure water 67.5%) to detoxify nitrogen oxides (NOx).

Specifically, the urea water added ₍ injected) from the urea water addition valve 68 is hydrolyzed by the exhaust heat of the exhaust gas. be done.
( _NH2 )2CO+ _H2O → _2NH3 + _CO2 ( ₁ )

When the exhaust gas passes through the SCR-DPF 63, nitrogen oxides (NOx) in the exhaust gas are selectively reduced and purified by ammonia (NH ₃ ) adsorbed on the surface of each small hole of the honeycomb structure. . At that time, NOx is reduced and purified by the reduction reactions shown in the following formulas (2) to (4).
4NO+ _{4NH3 + O2} →4N2+6H2O ( ₂ )
6NO ₂ +8NH ₃ →7N ₂ +12H ₂ O (3)
NO+NO2 _{+ 2NH3-} >2N2 _{+ 3H2O} (4)

Further, the fuel addition valve 29 reacts with the exhaust gas in the oxidation catalyst (DOC) 62 when regenerating the SCR-DPF 63 on which particulate matter (PM) is accumulated (when burning and incinerating the particulate matter). It injects fuel to raise the temperature of the exhaust gas. Specifically, the fuel injected into the exhaust gas from the fuel addition valve 29 by a control signal from the ECU 80 undergoes an oxidation reaction with the oxygen remaining in the exhaust gas due to the noble metal carried on the oxidation catalyst (DOC) 62. The exhaust gas temperature rises due to the heat generated.

Then, when the temperature of the catalyst bed of the SCR-DPF 63 rises due to this high-temperature exhaust gas and reaches a predetermined temperature or higher (for example, 500° C. or higher), particulate matter (PM) accumulated in the SCR-DPF 63 burns. incinerated. By maintaining such a state for a predetermined time, the particulate matter (PM) accumulated in the SCR-DPF 63 is burned and removed, and the particulate matter (PM) in the exhaust gas is collected. The collection function of the DPF 63 can be restored (regenerated) (so-called filter regeneration processing).

The ECU 80 is a known one including a CPU, EEPROM, RAM, timer, backup RAM (not shown), and the like. The CPU executes various arithmetic processes based on various programs and various parameters stored in the EEPROM. In addition, the RAM temporarily stores the results of operations performed by the CPU and the data input from each detection device, and the EEPROM and the backup RAM store data to be saved, for example, when the engine 10 is stopped. do.

The ECU 80 is electrically connected to the fuel injection devices 15L and 15R, the intake switching valve 51, the intake bypass valve 52, the exhaust switching valve 53, the actuators 57B and 58B, the fuel addition valve 29, the urea water addition valve 68, and the like. The ECU 80 also includes an intake air flow rate detection device 6, a pressure sensor 23, a first exhaust temperature detection device 25, a second exhaust temperature detection device 26, an intake air temperature detection device 27, an engine speed detection device 28, a boost pressure sensor 55, and a , nozzle opening sensors 57C and 58C, an intermediate exhaust temperature detector 66, a downstream exhaust temperature detector 67, a NOx sensor 69, and an accelerator pedal depression amount detector 71. The accelerator pedal depression amount detection device 71 is, for example, an accelerator pedal depression angle sensor, and is provided on the accelerator pedal.

The ECU 80 can detect the intake air flow rate taken by the engine 10 based on the detection signal from the intake air flow rate detection device 6 . The ECU 80 can detect the temperature of the exhaust gas flowing into the oxidation catalyst (DOC) 62 from the outlet side of the main turbine 21A based on the detection signal from the first exhaust temperature detection device 25 . The ECU 80 can detect the rotation speed, rotation angle, etc. of the crankshaft of the engine 10 based on the detection signal from the engine rotation speed detection device 28 .

The ECU 80 can detect the temperature of the exhaust gas flowing out of the oxidation catalyst (DOC) 62 and flowing into the SCR-DPF 63 based on the detection signal from the intermediate exhaust temperature detection device 66 . The ECU 80 can detect the temperature of the exhaust gas flowing out from the SCR-DPF 63 based on the detection signal from the downstream side exhaust temperature detection device 67 . The ECU 80 can detect the amount of depression of the accelerator pedal by the driver (the driver's request for acceleration or deceleration) based on the detection signal from the accelerator pedal depression amount detection device 71 .

The ECU 80 also outputs a valve opening signal for opening or closing the intake switching valve 51, the intake bypass valve 52, and the exhaust switching valve 53 according to the operating state. The ECU 80 also outputs drive signals for driving the actuators 57B and 58B based on the detection signals of the nozzle opening sensors 57C and 58C, and adjusts the nozzle opening of the plurality of variable nozzles 57A and 58A. Further, the ECU 80 outputs control signals for driving the fuel injection devices 15L and 15R based on detection signals from the engine speed detection device 28, the accelerator pedal depression amount detection device 71, etc., and directly injects fuel into each cylinder. Controls the amount of fuel injection.

Next, in the exhaust gas purification system 1 configured as described above, a "twin turbo mode" in which the main turbocharger 21 and the sub-turbocharger 22 are operated to perform supercharging, which is executed by the ECU 80; Control for switching to the "single turbo mode" in which only the main turbocharger 21 operates and is supercharged will be described with reference to FIGS. 2 and 3. FIG. First, the selection of the "single turbo mode" and the "twin turbo mode" will be described with reference to FIG. FIG. 2 shows an example of an operating region map that determines the operating regions of the single-turbo mode and the twin-turbo mode.

In FIG. 2, the horizontal axis indicates the engine speed, and the vertical axis indicates the required torque (fuel injection amount). A solid line 81 indicates the operating characteristic of the "single turbo mode", and a dashed line 82 indicates the operating characteristic of the "twin turbo mode". When the operating point determined by the engine speed and the required torque (fuel injection amount) is below the solid line 81, the engine 10 operates in "single turbo mode". Further, when the engine speed and the required torque increase and the operating point enters the region above the solid line 81, the engine 10 operates in "twin turbo mode". That is, when the operating point is below the switching line surrounded by the dashed line 83, the "single turbo mode" is selected, and when it is above the switching line, the "twin turbo mode" is selected.

Next, the setting states of the exhaust switching valve 53, the intake switching valve 51, and the intake bypass valve 52 set by the ECU 80 in each supercharging mode will be described based on the supercharging mode setting map 85 shown in FIG. The supercharging mode setting map 85 is stored in advance in the EEPROM, and the ECU 80 controls opening/closing of the exhaust switching valve 53, the intake switching valve 51, and the intake bypass valve 52 based on the supercharging mode setting map 85. Set the valve.

As shown in FIG. 3, when the engine 10 is operated in the "single turbo mode", the ECU 80 outputs control signals for closing the exhaust switching valve 53, the intake switching valve 51, and the intake bypass valve 52. The exhaust switching valve 53, the intake switching valve 51, and the intake bypass valve 52 are all set to the "closed state". The ECU 80 also reads out the single turbo mode flag from the RAM, sets it to "ON", and stores it in the RAM again. The ECU 80 also reads out the twin switching mode flag, the twin turbo mode flag, and the single switching mode flag from the RAM, sets them to "OFF", and stores them in the RAM again.

Further, when switching the engine 10 from the "single turbo mode" to the "twin turbo mode", the ECU 80 operates in the "twin switching mode" to the twin turbo mode, for example, for about 0.5 seconds to 1 second. , operate in "twin turbo mode". When operating the engine 10 in the "twin switching mode" to the twin turbo mode, the ECU 80 maintains the "closed state" of the intake switching valve 51 and opens the exhaust switching valve 53 and the intake bypass valve 52. to set the exhaust switching valve 53 and the intake bypass valve 52 to the "valve open state".

As a result, the auxiliary turbocharger 22 is operated to increase the rotation of the auxiliary turbine 22A to the rotation in the "twin turbo mode", and the intake air pressurized by the auxiliary compressor 22B flows through the intake bypass pipe 36 and the intake pipe 31L. and supplied to the inlet side of the main compressor 21B. The ECU 80 also reads out the twin switching mode flag from the RAM, sets it to "ON", and stores it in the RAM again. In addition, the ECU 80 reads the single turbo mode flag, the twin turbo mode flag, and the single switching mode flag from the RAM, sets them to "OFF", and stores them in the RAM again.

Thereafter, when operating the engine 10 in the "twin turbo mode", the ECU 80 maintains the "valve open state" of the exhaust switching valve 53 and outputs a control signal for opening the intake switching valve 51 to " At the same time, a valve closing control signal is output to the intake bypass valve 52 to set it to a "valve closed state." The ECU 80 also reads out the twin turbo mode flag from the RAM, sets it to "ON", and stores it in the RAM again. The ECU 80 also reads out the single turbo mode flag, the twin switching mode flag, and the single switching mode flag from the RAM, sets them to "OFF", and stores them in the RAM again. As a result, the intake air pressurized by the main compressor 21B and the sub-compressor 22B is supplied to the intake manifold 34 via the intake pipes 32L, 32R, 33. As shown in FIG.

Further, when switching the engine 10 from the "twin turbo mode" to the "single turbo mode", the ECU 80 operates in the "single switching mode" to the single turbo mode for about 0.5 seconds to 1 second, for example. , to operate in "single turbo mode". When the engine 10 is operated in the "single switching mode" to the single turbo mode, the ECU 80 outputs a valve closing control signal to the exhaust switching valve 53 and the intake switching valve 51 to set them to the "valve closed state". , outputs a valve opening control signal to the intake bypass valve 52 to set it to the "valve open state".

As a result, even if the exhaust switching valve 53 is in the "closed state", the sub-turbine 22A rotates due to inertia, but the intake air pressurized by the sub-compressor 22B passes through the intake bypass pipe 36 and the intake pipe 31L. It is supplied to the inlet side of the compressor 21B and is not supplied to the intake pipe 33. After that, when the rotation of the secondary turbine 22A decreases, the ECU 80 causes the engine 10 to operate in "single turbo mode". The ECU 80 also reads out the single switching mode flag from the RAM, sets it to "ON", and stores it in the RAM again. The ECU 80 also reads out the single turbo mode flag, the twin switching mode flag, and the twin turbo mode flag from the RAM, sets them to "OFF", and stores them in the RAM again.

[Filter regeneration process]
Next, in the exhaust purification system 1 configured as described above, an example of "filter regeneration processing" for burning and removing particulate matter (PM) trapped in the SCR-DPF 63 by the ECU 80 will be described with reference to FIGS. 14. During operation of the engine 10, the ECU 80 repeatedly executes the processing procedure shown in the flowchart of FIG.

As shown in FIG. 4, first, in step S11, the ECU 80 reads the filter regeneration request flag from the RAM and determines whether or not it is set to "ON". When the filter regeneration request flag is set to "ON", the particulate matter (PM) deposited on the SCR-DPF 63 reaches a predetermined PM deposition amount W3 (for example, approximately 50 g), and the SCR-DPF 63 is regenerated. This indicates that the collection function needs to be restored. Note that the filter regeneration request flag is set to "OFF" and stored in the RAM when the ECU 80 is activated.

Then, when it is determined that the filter regeneration request flag is set to "ON" (S11: YES), the ECU 80 proceeds to the process of step S16, which will be described later. On the other hand, when it is determined that the filter regeneration request flag is set to "OFF" (S11: NO), the ECU 80 proceeds to the process of step S12. In step S12, the ECU 80 executes a sub-process of "PM accumulation state acquisition process", and then proceeds to the process of step S13. The "PM deposition state acquisition process" is collected by the SCR-DPF 63 during a predetermined time interval (for example, intervals of several tens of milliseconds to several hundreds of milliseconds). This is a process of acquiring the amount (PM deposition amount).

[PM Accumulation State Acquisition Processing]
Details of the sub-processing of the "PM accumulation state acquisition processing" will now be described with reference to FIG. As shown in FIG. 5, first, in step S111, the ECU 80 detects the engine speed of the engine 10 and the engine load (fuel injection amount) based on detection signals from the accelerator pedal depression amount detection device 71, the engine speed detection device 28, and the like. ) and the like and stored in the RAM, the process proceeds to step S112.

In step S112, based on a map (not shown) showing the relationship between the operating state of the engine 10 and the deposition amount of particulate matter (PM) per unit time, the ECU 80 controls the operation at predetermined time intervals (for example, several tens of milliseconds to several hundreds of milliseconds). interval), the amount of particulate matter (PM) deposited on the SCR-DPF 63 is calculated, and the process proceeds to step S113. In step S113, the ECU 80 adds the accumulated amount of particulate matter (PM) calculated in step S112 (hereinafter also referred to as "PM accumulated amount") to the previously calculated PM accumulated amount of the SCR-DPF 63, and stores it in the EEPROM. , the sub-process is terminated, the process returns to the main flowchart, and the process proceeds to step S13.

Specifically, in step S113, the ECU 80 sets a count value corresponding to the PM accumulation amount calculated in step S112 to a PM counter representing the PM accumulation amount accumulated in the entire SCR-DPF 63 provided in the EEPROM. After adding it to the count value and updating the PM counter, the sub-process is terminated, the process returns to the main flowchart, and the process proceeds to step S13. Therefore, the count value of the PM counter provided in the EEPROM indicates the accumulation amount of particulate matter (PM) accumulated on the entire SCR-DPF 63 (PM accumulation amount).

Next, as shown in FIG. 4, in step S13, the ECU 80 reads the count value of the PM counter from the EEPROM and determines whether or not the count value of the PM counter is equal to or greater than the regeneration start threshold value C1. In other words, the ECU 80 burns the particulate matter (PM) deposited on the SCR-DPF 63 to determine whether or not it is necessary to regenerate the particulate matter (PM) trapping function of the SCR-DPF 63. do. Then, when it is determined that the count value of the PM counter is less than the regeneration start threshold value C1, that is, when it is determined that it is not necessary to regenerate the collecting function of the SCR-DPF 63 for collecting particulate matter (PM), (S13: NO), the ECU 80 ends the process.

On the other hand, when it is determined that the count value of the PM counter is equal to or greater than the regeneration start threshold value C1, that is, it is determined that the collecting function of the SCR-DPF 63 for collecting particulate matter (PM) needs to be regenerated. If so (S13: YES), the ECU 80 proceeds to the process of step S14. In step S14, the ECU 80 reads from the RAM a filter regeneration request flag indicating that it is necessary to regenerate the collecting function of the SCR-DPF 63 for collecting particulate matter (PM), sets it to "ON", and sets it to "ON" again. After storing in the RAM, the process proceeds to step S15.

In step S15, the ECU 80 reads the aqueous urea solution addition permission flag from the RAM, sets it to "OFF" and stores it in the RAM again, and then proceeds to the process of step S16. When the urea water addition permission flag is set to "OFF", the urea water addition valve 68 does not permit addition (spraying) of urea water (reducing agent solution) of a predetermined concentration toward the SCR-DPF 63. express the purpose. As a result, it is executed by the ECU 80 at a timing different from the "filter regeneration process", and is directed to the SCR-DPF 63 in the exhaust gas every predetermined time (for example, 200 milliseconds to 400 milliseconds). Execution of the "urea water addition process" for adding (spraying) urea water (reducing agent solution) is stopped.

The urea water addition permission flag is set to "ON" and stored in the RAM when the ECU 80 is activated. When the urea water addition permission flag is set to "ON", the urea water addition valve 68 permits addition (spraying) of urea water (reducing agent solution) of a predetermined concentration toward the SCR-DPF 63. express the purpose. As a result, it is executed by the ECU 80 at a timing different from the "filter regeneration process", and is directed to the SCR-DPF 63 in the exhaust gas every predetermined time (for example, 200 milliseconds to 400 milliseconds). A "urea water addition process" for adding (spraying) urea water (reducing agent solution) is executed.

In step S<b>16 , the ECU 80 detects the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 via the first exhaust temperature detection device 25 . Then, the ECU 80 determines whether or not the exhaust gas temperature TG is equal to or higher than the fuel addition permission temperature TS. That is, the ECU 80 determines whether the temperature of the exhaust gas flowing into the oxidation catalyst (DOC) 62 is equal to or higher than the permission temperature for adding (injecting) fuel via the fuel addition valve 29 . The fuel addition permission temperature TS is obtained in advance by CAE (Computer Aided Engineering) analysis or experiment, is set to about 250° C. to 300° C., and is stored in EEPROM in advance.

When it is determined that the exhaust gas temperature TG is lower than the fuel addition permission temperature TS (S16: NO), the ECU 80 determines that the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 is lower than the fuel addition permission temperature TS. Wait until it rises above On the other hand, when it is determined that the exhaust gas temperature TG is equal to or higher than the fuel addition permission temperature TS (S16: YES), the ECU 80 proceeds to the process of step S17.

In step S17, the ECU 80 executes the sub-process of "fuel addition amount acquisition process", and then proceeds to the process of step S18. A sub-process of the “fuel addition amount acquisition process” is a process of acquiring the addition amount of fuel to be added (injected) from the fuel addition valve 29 into the exhaust gas.

[Fuel Addition Amount Acquisition Processing]
Here, the details of the sub-processing of the "fuel addition amount acquisition process" will be described with reference to FIGS. 6 and 8 to 11. FIG. As shown in FIG. 6, first, in step S211, the ECU 80 detects the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 via the first exhaust temperature detection device 25, and stores it in the RAM. The process proceeds to step S212.

In step S<b>212 , the ECU 80 calculates the intake air flow rate GA [g/sec] from the detection signal input from the intake air flow rate detection device 6 . Further, the ECU 80 reads from the RAM the fuel injection amounts instructed to the respective fuel injection devices 15L and 15R from the present to a predetermined time (for example, one second) before. After storing the total value of the intake air flow rate GA and the fuel injection amount as the exhaust gas flow rate GG [g/sec] in the RAM, the ECU 80 proceeds to step S213. The ECU 80 may calculate the intake air flow rate GA [g/sec] from the detection signal input from the intake air flow rate detection device 6 and store it in the RAM as the exhaust gas flow rate GG [g/sec].

In step S213, the ECU 80 reads from the EEPROM a target catalyst bed temperature TF (for example, approximately 500° C.) for the SCR-DPF 63 that can burn particulate matter (PM) deposited on the SCR-DPF 63 . The ECU 80 also reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG [g/sec] calculated in step S212. The target catalyst bed temperature TF (for example, about 500° C.) of the SCR-DPF 63 is a value set in advance through experiments and simulations, and stored in EEPROM in advance.

Then, the ECU 80 determines the required fuel addition amount Q [mm ³ /sec] is calculated using the following equation (5) and stored in the RAM, and then the process proceeds to step S214. Note that "K" in the following equation (5) is a model constant, a value preset through experiments and simulations, and stored in EEPROM in advance.

Required fuel addition amount Q=exhaust gas flow rate GG×(target catalyst bed temperature TF−exhaust gas temperature TG)×K (5)

In step S214, the ECU 80 determines whether or not the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is a "single turbo mode" in which only the main turbocharger 21 operates and supercharges. That is, the ECU 80 reads the single turbo mode flag (see FIG. 3) from the RAM and determines whether or not the single turbo mode flag is set to "ON". Then, when it is determined that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "single turbo mode", that is, when it is determined that the single turbo mode flag is set to "ON". (S214: YES), the ECU 80 proceeds to the process of step S215.

In step S215, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG [g/sec] calculated in step S212. Then, the ECU 80 uses the single turbo mode fuel restriction addition amount map M11 (single turbo mode map) shown in FIG. A limited fuel addition amount [mm ³ /sec] in the single turbo mode corresponding to the exhaust gas flow rate GG [g/sec] is calculated.

Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. The process proceeds to S219. Note that the fuel restriction addition amount map M11 for the single turbo mode is pre-stored in the EEPROM.

Here, as shown in FIG. 8, when the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 is constant, for example, when it is constant at 300 [° C.], the exhaust gas flow rate GG [g/ sec], the amount of fuel added per unit time from the fuel addition valve 29 to the exhaust gas becomes smaller where the HC concentration [ppm] discharged from the tail pipe reaches the white smoke limit concentration where white smoke does not occur. . That is, when the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 is kept constant, the white smoke added from the fuel addition valve 29 to the exhaust gas increases as the exhaust gas flow rate GG [g/sec] increases. The upper limit value of the fuel addition amount (the limited fuel addition amount [mm ³ /sec]) becomes small.

Further, as shown in FIG. 9, when the exhaust gas flow rate GG [g/sec] flowing into the oxidation catalyst (DOC) 62 is constant, for example, when it is constant at 80 [g/sec], oxidation As the exhaust gas temperature TG flowing into the catalyst (DOC) 62 increases, the HC concentration [ppm] discharged from the tail pipe becomes the white smoke limit concentration at which white smoke does not occur. The amount of fuel added per hour is increased. That is, when the exhaust gas flow rate GG [g/sec] flowing into the oxidation catalyst (DOC) 62 is constant, the higher the temperature TG of the exhaust gas flowing into the oxidation catalyst (DOC) 62, the more The upper limit of the amount of fuel added to the exhaust gas that does not produce white smoke (limited fuel addition amount [mm ³ /sec]) increases.

Therefore, as shown in FIG. 10, the limited fuel addition amount map M11 for the single turbo mode is based on the relationships shown in FIGS. The inflowing exhaust gas temperature TG [°C] is used as a parameter. Further, the fuel restriction addition amount map M11 shows that when the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "single turbo mode", the fuel added from the fuel addition valve 29 into the exhaust gas does not emit white smoke. The upper limit of the addition amount (fuel limit addition amount [mm ³ /sec]) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is mapped.

As a result, the restricted fuel addition amount [mm ³ /sec] stored in the fuel restriction addition amount map M11 for the single turbo mode decreases as the exhaust gas flow rate GG [g/sec] increases, and the oxidation catalyst (DOC) It is set to increase as the exhaust gas temperature TG [° C.] flowing into 62 increases. 10, the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG calculated in step S212 [g/sec] is a value between points on the map, the upper limit value of the fuel addition amount (fuel limit addition amount [mm ³ /sec]) is calculated by interpolation processing.

On the other hand, as shown in FIG. 6, when it is determined in step S214 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is not in the "single turbo mode", that is, the single turbo mode flag is "OFF". (S214: NO), the ECU 80 proceeds to the process of step S216. In step S216, the ECU 80 determines whether or not the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is the "twin turbo mode" in which the main turbocharger 21 and the sub-turbocharger 22 operate to supercharge. judge.

That is, the ECU 80 reads the twin turbo mode flag (see FIG. 3) from the RAM and determines whether or not the twin turbo mode flag is set to "ON". Then, when it is determined that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin turbo mode", that is, when it is determined that the twin turbo mode flag is set to "ON". (S216: YES), the ECU 80 proceeds to the process of step S217.

In step S217, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG [g/sec] calculated in step S212. Then, the ECU 80 uses the twin-turbo mode fuel restriction addition amount map M12 (twin-turbo mode map) shown in FIG. The exhaust gas flow rate GG [g/sec] and the fuel limit addition amount [mm ³ /sec] corresponding to the twin turbo mode are calculated.

Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. The process proceeds to S219. Note that the fuel restriction addition amount map M12 for the twin turbo mode is pre-stored in the EEPROM.

Here, as shown in FIG. 11, the fuel restriction addition amount map M12 for the twin turbo mode is based on the relationships shown in FIGS. and the exhaust gas temperature TG [° C.] flowing into . The limited fuel addition amount map M12 indicates that the fuel added from the fuel addition valve 29 into the exhaust gas does not emit white smoke when the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin turbo mode". The upper limit of the addition amount (fuel limit addition amount [mm ³ /sec]) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is mapped.

As a result, the restricted fuel addition amount [mm ³ /sec] stored in the fuel restriction addition amount map M12 for the twin-turbo mode decreases as the exhaust gas flow rate GG [g/sec] increases. It is set to increase as the exhaust gas temperature TG [° C.] flowing into 62 increases. 11, the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG calculated in step S212 [g/sec] is a value between points on the map, the upper limit value of the fuel addition amount (fuel limit addition amount [mm ³ /sec]) is calculated by interpolation processing.

On the other hand, as shown in FIG. 6, when it is determined in step S216 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is not in the "twin turbo mode," that is, the twin turbo mode flag is "OFF." (S216: NO), the ECU 80 proceeds to the process of step S218. That is, the ECU 80 switches the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 from the "single turbo mode" to the "twin turbo mode" in the "twin switching mode", or from the "twin turbo mode" to the "single turbo mode". mode", and the process proceeds to step S218.

In step S218, the ECU 80 sets "0 [mm ³ /sec]" to the exhaust gas from the fuel addition valve 29. The upper limit of the fuel addition amount that does not cause white smoke (fuel addition amount [mm ³ /sec]) , and then proceeds to the processing of step S219. That is, the ECU 80 controls the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 to operate in the "twin switching mode" or the "single switching mode", for example, for about 0.5 seconds to 1 second. After the fuel addition valve 29 is set so as not to add (inject) fuel into the exhaust gas, the process proceeds to step S219.

In step S219, the ECU 80 determines the required fuel addition amount Q [mm ³ /sec] calculated in step S213 and the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 into the exhaust gas without causing white smoke. The limited addition amount [mm ³ /sec] is read out from the RAM. Then, the ECU 80 determines whether or not the requested fuel addition amount Q is equal to or less than the restricted fuel addition amount. That is, the ECU 80 determines whether or not the required fuel addition amount Q is a fuel addition amount that does not emit white smoke from the tail pipe when added from the fuel addition valve 29 to the exhaust gas.

Then, when it is determined that the required fuel addition amount Q is equal to or less than the restricted fuel addition amount (S219: YES), the ECU 80 proceeds to the process of step S220. That is, the ECU 80 determines that the required fuel addition amount Q is a fuel addition amount that does not produce white smoke from the tail pipe when added from the fuel addition valve 29 to the exhaust gas (S219: YES), and step S220. proceed to the processing of In step S220, the ECU 80 stores the required fuel addition amount Q [mm ³ /sec] in the RAM as the fuel addition amount [mm ³ /sec] to be added to the exhaust gas from the fuel addition valve 29, and then executes the sub-process. When finished, the process returns to the main flow chart and proceeds to the process of step S18.

On the other hand, when it is determined that the required fuel addition amount Q is a fuel addition amount larger than the restricted fuel addition amount (S219: NO), the ECU 80 proceeds to the process of step S221. That is, the ECU 80 determines that the required fuel addition amount Q is a fuel addition amount that produces white smoke from the tail pipe when added to the exhaust gas from the fuel addition valve 29 (S219: NO), and step S221. proceed to the processing of

In step S221, the ECU 80 sets a limited fuel addition amount [mm ³ /sec], which is the upper limit of the amount of fuel to be added from the fuel addition valve 29 into the exhaust gas without causing white smoke, into the exhaust gas from the fuel addition valve 29. After the amount of added fuel [mm ³ /sec] is stored in the RAM, the sub-process is finished, the process returns to the main flow chart, and the process proceeds to step S18.

As a result, in each of the "single turbo mode" and the "twin turbo mode", which are the supercharging states of the main turbocharger 21 and the sub-turbocharger 22, the amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 per unit time It is possible to set the added amount per unit to be equal to or less than the fuel limit added amount. As a result, the entire amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 can be oxidized by the oxidation catalyst (DOC) 62 to raise the temperature of the exhaust gas. Therefore, in the engine 10 equipped with the main turbocharger 21 and the sub-turbocharger 22 in parallel, the particulate matter (PM) collection of the SCR-DPF 63 is prevented without causing white smoke in the exhaust gas discharged from the tail pipe. function can be played.

In addition, when the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is the "twin switching mode" or the "single switching mode", the state of the exhaust gas on the inlet side of the oxidation catalyst (DOC) 62 The amount of change that changes from time to time (such as the effect of the swirling flow of the exhaust gas and the mixed state of the additive fuel and the exhaust gas.) growing. Therefore, in the "twin switching mode" or the "single switching mode", the ECU 80 sets the upper limit value of the fuel addition amount (fuel addition amount limit) to be added (injected) from the fuel addition valve 29 into the exhaust gas to "0 [ mm ³ /sec]", it is possible to effectively suppress the generation of white smoke in the exhaust gas.

In addition, the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 operates in the "twin switching mode" or the "single switching mode", for example, for about 0.5 seconds to 1 second. A decrease in catalyst bed temperature of the catalyst (DOC) 62 can be effectively suppressed. As a result, the ECU 80 can reproduce the particulate matter (PM) trapping function of the SCR-DPF 63 without generating white smoke in the exhaust gas discharged from the tail pipe.

As shown in FIG. 4, in step S18, the ECU 80 determines whether or not the fuel addition execution timing for adding fuel from the fuel addition valve 29 has arrived. This fuel execution timing is, for example, the timing at which the first cylinder reaches the exhaust stroke, that is, the fuel addition execution timing is reached every time the crank angle rotates by 720°. As a result, by performing fuel addition from the fuel addition valve 29 in synchronism with the exhaust stroke of the first cylinder, the added fuel is easily diffused into the exhaust gas.

Then, when it is determined that the fuel addition execution timing for adding fuel from the fuel addition valve 29 has not come (S18: NO), the ECU 80 terminates the process. On the other hand, when it is determined that the fuel addition execution timing for adding fuel from the fuel addition valve 29 has arrived (S18: YES), the ECU 80 proceeds to the process of step S19. In step S19, the ECU 80 reads again from the RAM the fuel addition amount [mm ³ /sec] to be added to the exhaust gas from the fuel addition valve 29 stored in the RAM in step S220 or S221.

Then, the ECU 80 multiplies this fuel addition amount [mm ³ /sec] by the time interval for starting the process shown in FIG. After adding (injecting) the fuel of the fuel addition amount [mm ³ ] calculated through the fuel addition valve 29 into the exhaust gas, the process proceeds to step S20. In step S20, the ECU 80 executes the "PM counter update process" sub-process, and then proceeds to the process of step S21. A sub-process of the "PM counter update process" is a process of subtracting a count value corresponding to incinerated particulate matter (PM) from a PM counter (not shown).

[PM counter update process]
Here, the details of the sub-processing of "PM counter update processing" will be described with reference to FIGS. 7 and 12. FIG. As shown in FIG. 7, first, in step S311, the ECU 80 detects the exhaust gas temperature T2 flowing into the SCR-DPF 63 based on the detection signal from the intermediate exhaust gas temperature detection device 66, and stores it in the RAM. Further, the ECU 80 detects the exhaust gas temperature T3 flowing out of the SCR-DPF 63 based on the detection signal from the downstream side exhaust temperature detection device 67, stores it in the RAM, and then proceeds to the processing of step S312.

In step S312, the ECU 80 performs SCR- After calculating (estimating) the catalyst bed temperature TP1 of the DPF 63 and storing it in the RAM, the process proceeds to step S313.

In step S313, the ECU 80 reads the catalyst bed temperature TP1 of the SCR-DPF 63 from the RAM. Then, the ECU 80 reads the "PM combustion lower limit temperature TD1" from the EEPROM and determines whether or not the current catalyst bed temperature TP1 of the SCR-DPF 63 is equal to or higher than the "PM combustion lower limit temperature TD1". The "PM combustion lower limit temperature TD1" is the lower limit temperature at which particulate matter (PM) is combusted and incinerated, and is, for example, approximately 500°C to 600°C, and is pre-stored in the EEPROM.

Then, when it is determined that the current catalyst bed temperature TP1 of the SCR-DPF 63 is less than the "PM combustion lower limit temperature TD1" (S313: NO), the ECU 80 terminates the sub-processing and Returning to the main flowchart, the process proceeds to step S21. On the other hand, when it is determined that the current catalyst bed temperature TP1 of the SCR-DPF 63 is equal to or higher than the "PM combustion lower limit temperature TD1" (S313: YES), the ECU 80 proceeds to the process of step S314.

In step S314, the ECU 80 uses the PM burning speed map M21 that associates the relationship between the catalyst bed temperature of the SCR-DPF 63 and the PM burning speed shown in FIG. After acquiring the PM burning rate corresponding to the temperature TP1 and storing it in the RAM, the process proceeds to step S315. The PM burning rate is the amount of particulate matter (PM) burned per unit volume and per unit time inside the SCR-DPF 63 .

FIG. 12 shows an example of the relationship between the catalyst bed temperature TP1 of the SCR-DPF 63 and the PM burning rate. As shown in FIG. 12, in the PM burning speed map M21, the higher the catalyst bed temperature TP1 of the SCR-DPF 63, the faster the PM burning speed at which particulate matter (PM) burns. Incidentally, the PM burning speed map M21 for obtaining the PM burning speed is obtained in advance by CAE (Computer Aided Engineering) analysis or experimentation, and is stored in EEPROM in advance according to maps and formulas.

As shown in FIG. 7, in step S315, the ECU 80 reads the PM burning rate corresponding to the catalyst bed temperature TP1 of the SCR-DPF 63 from the RAM, and also reads the volume of the SCR-DPF 63 from the EEPROM. Then, the ECU 80 multiplies the PM combustion speed by the volume of the SCR-DPF 63 and a predetermined time (for example, the time between injections of fuel by the fuel addition valve 29), and the fuel in the SCR-DPF 63 within the predetermined time. Calculate the amount of combusted particulate matter (PM).

Subsequently, the ECU 80 subtracts the calculated count value corresponding to the amount of particulate matter (PM) burned from the count value of the PM counter provided in the EEPROM, then terminates the sub-processing, and returns to the main flowchart. Return to step S21. In other words, the ECU 80 determines that the amount of particulate matter that is burned in the SCR-DPF 63 within a predetermined time (for example, the time between fuel injections by the fuel addition valve 29) from the amount of PM deposited in the SCR-DPF 63. After subtracting the amount of combustion of (PM), the sub-process is finished, the process returns to the main flow chart, and the process proceeds to step S21.

As shown in FIG. 4, in step S21, the ECU 80 reads the count value of the PM counter provided in the EEPROM and determines whether or not the count value of the PM counter is smaller than the "regeneration end threshold value C2". That is, the ECU 80 determines whether or not substantially all of the particulate matter (PM) within the SCR-DPF 63 has been burned. Then, when it is determined that the count value of the PM counter is equal to or greater than the "regeneration end threshold value C2" (S21: NO), the ECU 80 determines that all the particulate matter (PM) in the SCR-DPF 63 has not yet been burned. It is determined that there is not, and the process ends.

On the other hand, when determining that the count value of the PM counter is smaller than the "regeneration end threshold value C2" (S21: YES), the ECU 80 determines that substantially all of the particulate matter (PM) in the SCR-DPF 63 has been burned. Then, the injection (addition) of fuel by the fuel addition valve 29 is terminated, and the process proceeds to step S22. In step S22, the ECU 80 reads the filter regeneration request flag from the RAM, sets it to "OFF" and stores it in the RAM again, and then proceeds to the process of step S23. In step S23, the ECU 80 reads the aqueous urea solution addition permission flag from the RAM, sets it to "ON", stores it in the RAM again, and then terminates the process.

When the urea water addition permission flag is set to "ON", the urea water addition valve 68 permits addition (spraying) of urea water (reducing agent solution) of a predetermined concentration toward the SCR-DPF 63. express the purpose. As a result, it is executed by the ECU 80 at a timing different from the "filter regeneration process", and is directed to the SCR-DPF 63 in the exhaust gas every predetermined time (for example, 200 milliseconds to 400 milliseconds). Execution of the "urea water addition process" for adding (spraying) urea water (reducing agent solution) is started again. As a result, when the exhaust gas passes through the SCR-DPF 63, nitrogen oxides (NOx) in the exhaust gas are selectively reduced and purified by ammonia (NH ₃ ) adsorbed on the surface of each small hole of the honeycomb structure. At the same time, particulate matter (PM) is trapped inside the SCR-DPF 63 .

Here, engine 10 functions as an example of an internal combustion engine. The exhaust gas purification device 61 functions as an example of a purification catalyst device. The intake air flow rate detection device 6 and the ECU 80 constitute an example of an exhaust gas flow rate acquisition device. The ECU 80 functions as an example of a supercharging state acquisition device, a limited addition amount calculation device, a deposition amount acquisition device, a deposition amount determination device, and a reducing agent addition stop setting device. The fuel restriction addition amount map M11 for single turbo functions as an example of a map for single turbo mode. The fuel restriction addition amount map M12 for twin-turbo mode functions as an example of a map for twin-turbo mode. The urea water addition valve 68 functions as an example of a reducing agent addition valve.

Further, the numerical values used in the description of the above embodiment are examples, and the present invention is not limited to these numerical values. Greater than (≧), less than (≦), greater than (>), less than (<), etc. may or may not include an equal sign.

The exhaust purification system of the present invention is not limited to the configuration, structure, appearance, shape, processing procedure, etc. described in the above embodiment, and various modifications, improvements, and additions can be made without changing the gist of the present invention. , can be deleted. In the following description, the same reference numerals as those of the engine 10 and the like according to the embodiment shown in FIGS. 1 to 12 denote the same or corresponding parts as the engine 10 and the like according to the embodiment.

[Another First Embodiment]
(A) For example, in step S17 described above, instead of the sub-process of the "fuel addition amount acquisition process" (see FIG. 6), the sub-process of the "second fuel addition amount acquisition process" shown in FIG. 13 is executed. You may make it progress to the process of step S18. Here, the sub-process of the "second fuel addition amount acquisition process" will be described with reference to FIGS. 13 to 15. FIG. As shown in FIG. 13, the sub-process of the "second added fuel amount acquisition process" has substantially the same procedure as the sub-process of the above-described "added fuel amount acquisition process" (see FIG. 6).

However, if it is determined in step S216 that the supercharging states of the main turbocharger 21 and the sub-turbocharger 22 are not in the "twin turbo mode", that is, it is determined that the twin turbo mode flag is set to "OFF". If so (S216: NO), the ECU 80 is different in that it executes the processes of steps S311 to S313 instead of the process of step S218.

Specifically, as shown in FIG. 13, when it is determined in step S216 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is not in the "twin turbo mode," that is, when the twin turbo mode flag is set to " OFF" (S216: NO), the ECU 80 proceeds to the process of step S311. In step S311, the ECU 80 determines whether or not the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin switching mode" for switching from the "single turbo mode" to the "twin turbo mode".

That is, the ECU 80 reads the twin switching mode flag (see FIG. 3) from the RAM and determines whether or not the twin switching mode flag is set to "ON". Then, when it is determined that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin switching mode", that is, when it is determined that the twin switching mode flag is set to "ON". (S311: YES), the ECU 80 proceeds to the process of step S312.

At step S312, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected at step S211 and the exhaust gas flow rate GG [g/sec] calculated at step S212. Then, the ECU 80 uses the twin switching mode fuel restriction addition amount map M13 (twin switching mode map) shown in FIG. The exhaust gas flow rate GG [g/sec] and the fuel limit addition amount [mm ³ /sec] corresponding to the twin switching mode are calculated.

Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. Execute the following processes. Note that the fuel restriction addition amount map M13 for the twin switching mode is pre-stored in the EEPROM.

Here, as shown in FIG. 14, the twin switching mode fuel restriction addition amount map M13 is based on the relationships shown in FIGS. and the exhaust gas temperature TG [° C.] flowing into . Further, the fuel restriction addition amount map M13 indicates that when the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin switching mode", the fuel added from the fuel addition valve 29 into the exhaust gas does not emit white smoke. The upper limit of the addition amount (fuel limit addition amount [mm ³ /sec]) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is mapped.

As a result, the restricted fuel addition amount [mm ³ /sec] stored in the fuel restriction addition amount map M13 for the twin switching mode decreases as the exhaust gas flow rate GG [g/sec] increases, and the oxidation catalyst (DOC) It is set to increase as the exhaust gas temperature TG [° C.] flowing into 62 increases. 14, the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG calculated in step S212 [g/sec] is a value between points on the map, the upper limit value of the fuel addition amount (fuel limit addition amount [mm ³ /sec]) is calculated by interpolation processing.

On the other hand, as shown in FIG. 13, when it is determined in step S311 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is not in the "twin switching mode", that is, the twin switching mode flag is "OFF". (S311: NO), the ECU 80 proceeds to the process of step S312. That is, the ECU 80 determines that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "single switching mode" for switching from the "twin turbo mode" to the "single turbo mode", and proceeds to the process of step S312. move on.

At step S312, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected at step S211 and the exhaust gas flow rate GG [g/sec] calculated at step S212. 15 (single switching mode map), the ECU 80 determines the current exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 and the current A limited fuel addition amount [mm ³ /sec] in the single switching mode corresponding to the exhaust gas flow rate GG [g/sec] is calculated.

Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. Execute the following processes. It should be noted that the fuel restriction addition amount map M14 for the single switching mode is pre-stored in the EEPROM.

Here, as shown in FIG. 15, the fuel restriction addition amount map M14 for the single switching mode is based on the relationships shown in FIGS. and the exhaust gas temperature TG [° C.] flowing into . Further, the fuel restriction addition amount map M14 shows that when the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "single switching mode", the fuel added from the fuel addition valve 29 into the exhaust gas does not emit white smoke. The upper limit of the addition amount (fuel limit addition amount [mm ³ /sec]) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is mapped.

As a result, the restricted fuel addition amount [mm ³ /sec] stored in the fuel restriction addition amount map M14 for the single switching mode becomes smaller as the exhaust gas flow rate GG [g/sec] increases, and the oxidation catalyst (DOC) It is set to increase as the exhaust gas temperature TG [° C.] flowing into 62 increases. 15, the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG calculated in step S212 [g/sec] is a value between points on the map, the upper limit value of the fuel addition amount (fuel limit addition amount [mm ³ /sec]) is calculated by interpolation processing.

As a result, in each of the "single turbo mode", "twin turbo mode", "twin switching mode", and "single switching mode", which are the supercharging states of the main turbocharger 21 and the sub-turbocharger 22, The amount of unburned fuel added to the exhaust gas per unit time can be set to be equal to or less than the fuel limit addition amount. As a result, the entire amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 can be oxidized by the oxidation catalyst (DOC) 62 to raise the temperature of the exhaust gas.

Therefore, in the engine 10 equipped with the main turbocharger 21 and the sub-turbocharger 22 in parallel, the particulate matter (PM) collection of the SCR-DPF 63 is prevented without causing white smoke in the exhaust gas discharged from the tail pipe. function can be played. Also in the case of the "twin switching mode" and the "single switching mode", the ECU 80 can add (inject) fuel into the exhaust gas from the fuel addition valve 29, and the particulate matter (PM) of the SCR-DPF 63 ) can be shortened.

[Another Second Embodiment]
(B) In addition, for example, in step S17, instead of the sub-process of the "fuel addition amount acquisition process" (see FIG. 6), the sub-process of the "third fuel addition amount acquisition process" shown in FIG. 16 is executed. After that, the process may proceed to step S18. Here, the sub-process of the "third fuel addition amount acquisition process" will be described with reference to FIG. As shown in FIG. 16, the sub-process of the "third added fuel amount acquisition process" has substantially the same processing procedure as the sub-process of the above-described "second added fuel amount acquisition process" (see FIG. 13).

However, when it is determined in step S311 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin switching mode" (S311: YES), the ECU 80 performs the steps after step S217. They are different in that they perform processing. Further, when it is determined in step S311 that the supercharging states of the main turbocharger 21 and the sub-turbocharger 22 are not in the "twin switching mode" (S311: NO), the ECU 80 is in the "single switching mode." is determined, and the processes after step S215 are executed. Also, the fuel restriction addition amount map M13 (see FIG. 14) for the twin switching mode and the fuel restriction addition amount map M14 (see FIG. 15) for the single switching mode are different in that they are not pre-stored in the EEPROM.

Here, when the engine 10 is operated in the "twin switching mode", the ECU 80 sets the intake switching valve 51 to the "closed state" and sets the exhaust switching valve 53 and the intake bypass valve 52 to the "valve open state." ” (see FIG. 3). When operating the engine 10 in the "twin turbo mode", the ECU 80 sets the exhaust switching valve 53 and the intake switching valve 51 to the "valve open state" and sets the intake bypass valve 52 to the "valve closed state". do. Therefore, in the "twin switching mode" and the "twin turbo mode", the exhaust gas switching valve 53 is set to the "valve open state" in each of them, so the exhaust gas state quantity ( the effect of the swirling flow of the exhaust gas, the mixed state of the added fuel and the exhaust gas, etc.) are considered to be approximately the same state quantity.

Therefore, when it is determined in step S311 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "twin switching mode" (S311: YES), the ECU 80 proceeds to the process of step S217. You can also try to In step S217, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG [g/sec] calculated in step S212.

Then, the ECU 80 uses the twin-turbo mode fuel restriction addition amount map M12 (twin-turbo mode map) shown in FIG. The limited fuel addition amount [mm ³ /sec] in the twin-turbo mode corresponding to the exhaust gas flow rate GG [g/sec] may be calculated. Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. You may make it perform subsequent processes. Note that the fuel restriction addition amount map M12 (see FIG. 11) for the twin turbo mode is pre-stored in the EEPROM.

When operating the engine 10 in the "single switching mode", the ECU 80 sets the exhaust switching valve 53 and the intake switching valve 51 to the "closed state" and sets the intake bypass valve 52 to the "open state". do. Further, when the engine 10 is operated in the "single turbo mode", the ECU 80 sets the exhaust switching valve 53, the intake switching valve 51 and the intake bypass valve 52 all to the "closed state". Therefore, in the "single switching mode" and the "single turbo mode", the exhaust gas switching valve 53 is set to the "valve closed state" in each of them. the effect of the swirling flow of the exhaust gas, the mixed state of the added fuel and the exhaust gas, etc.) are considered to be approximately the same state quantity.

Therefore, when it is determined in step S311 that the supercharging state of the main turbocharger 21 and the sub-turbocharger 22 is in the "single switching mode" (S311: NO), the ECU 80 proceeds to the process of step S215. You can also try to In step S215, the ECU 80 reads from the RAM the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 detected in step S211 and the exhaust gas flow rate GG [g/sec] calculated in step S212.

Then, the ECU 80 uses the single turbo mode fuel restriction addition amount map M11 (single turbo mode map) shown in FIG. The limited fuel addition amount [mm ³ /sec] in the single turbo mode corresponding to the exhaust gas flow rate GG [g/sec] may be calculated. Then, the ECU 80 stores the calculated restricted fuel addition amount [mm ³ /sec] in the RAM as the upper limit value of the fuel addition amount to be added from the fuel addition valve 29 to the exhaust gas without causing white smoke. You may make it perform subsequent processes. Note that the fuel restriction addition amount map M11 (see FIG. 10) for the single turbo mode is pre-stored in the EEPROM.

As a result, in each of the "single turbo mode", "twin turbo mode", "twin switching mode", and "single switching mode", which are the supercharging states of the main turbocharger 21 and the sub-turbocharger 22, The amount of unburned fuel added to the exhaust gas per unit time can be set to be equal to or less than the fuel limit addition amount. As a result, the entire amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 can be oxidized by the oxidation catalyst (DOC) 62 to raise the temperature of the exhaust gas.

Therefore, in the engine 10 equipped with the main turbocharger 21 and the sub-turbocharger 22 in parallel, the particulate matter (PM) collection of the SCR-DPF 63 is prevented without causing white smoke in the exhaust gas discharged from the tail pipe. function can be played. Furthermore, since it is not necessary to store the fuel restriction addition amount map M13 (see FIG. 14) for the twin switching mode and the fuel restriction addition amount map M14 (see FIG. 15) for the single switching mode in advance in the EEPROM, the storage capacity of the ECU 80 is reduced. can be reduced.

[Another third embodiment]
(C) Further, for example, instead of the exhaust gas purification device 61, an exhaust gas purification device 86 (purification catalyst device) shown in FIG. 17 may be used. The exhaust gas purification device 86 will be described with reference to FIG. 17 . As shown in FIG. 17, the exhaust gas purifying device 86 has substantially the same configuration as the exhaust gas purifying device 61 . Therefore, the downstream side of the first exhaust pipe 46L and the downstream side of the second exhaust pipe 46R are connected and connected to the inflow port (inlet side) of the exhaust gas purifier 86 .

Further, downstream of the first exhaust pipe 46L, there is a first exhaust temperature detection device (for example, a temperature detection sensor) 25 for detecting the temperature of the inlet-side exhaust gas discharged from the main turbine 21A and flowing into the exhaust gas purification device 86. is provided. A fuel addition valve 29 is arranged in the first exhaust pipe 46L at a position downstream of the first exhaust temperature detection device 25 and upstream of the exhaust gas purification device 86 .

However, it differs in that an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 62 and a DPF (Diesel Particulate Filter) 87 instead of the SCR-DPF 63 are arranged from the upstream side inside the exhaust gas purification device 86. there is Further, the exhaust gas purification device 86 is provided with an intermediate exhaust gas temperature detection device 66 on the downstream side of the oxidation catalyst 62 and on the upstream side of the DPF 87, but is different in that the urea water addition valve 68 is not provided. ing. Therefore, the exhaust gas purification device 86 functions as an example of a purification catalyst device.

Also, in the filter regeneration process (see FIG. 4), the ECU 80 does not execute the processes of steps S15 and S23 because the urea water addition valve 68 is not arranged in the exhaust gas purification device 86. A urea water addition valve 68 and a selective reduction catalyst (SCR: Selective Catalytic Reduction) that renders NOx harmless may be arranged in the exhaust pipe on the downstream side of the DPF 87 .

The DPF 87 is formed in a columnar shape or the like from a porous member made of a ceramic material or the like, and has a honeycomb-structured cellular cylindrical body with a large number of small holes provided in the axial direction. different ends are closed by plugging members. The DPF 87 collects particulate matter (PM) by allowing the exhaust gas flowing into each small hole from the upstream side to pass through the porous material, and allows only the exhaust gas to flow out downstream through the adjacent small hole. .

As a result, in each of the "single turbo mode" and the "twin turbo mode", which are the supercharging states of the main turbocharger 21 and the sub-turbocharger 22, the amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 per unit time It is possible to set the added amount per unit to be equal to or less than the fuel limit added amount. As a result, the entire amount of unburned fuel added to the exhaust gas from the fuel addition valve 29 can be oxidized by the oxidation catalyst (DOC) 62 to raise the temperature of the exhaust gas. Therefore, in the engine 10 having the main turbocharger 21 and the sub-turbocharger 22 in parallel, the particulate matter (PM) trapping function of the DPF 87 can be used without causing white smoke in the exhaust gas discharged from the tail pipe. can be played.

[Another fourth embodiment]
(D) Further, for example, as shown in FIG. 18, the downstream side of the first exhaust pipe 46L and the downstream side of the second exhaust pipe 46R are connected and connected to the upstream side of the third exhaust pipe 88. You may do so. The downstream side of the third exhaust pipe 88 may be connected to the inlet of the exhaust gas purification device 61 . Further, the fuel addition valve 29 may be arranged downstream of the first exhaust pipe 46L, and the first exhaust temperature detection device 25 may be arranged in the third exhaust pipe 88. Accordingly, the ECU 80 can improve the detection accuracy of the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 based on the detection signal from the first exhaust temperature detection device 25 .

[Another Fifth Embodiment]
(E) Further, for example, as shown in FIG. 19, the downstream side of the first exhaust pipe 46L and the downstream side of the second exhaust pipe 46R are connected and connected to the upstream side of the third exhaust pipe 88. You may do so. The downstream side of the third exhaust pipe 88 may be connected to the inlet of the exhaust gas purification device 61 . Then, the first exhaust temperature detection device 25 may be provided in the third exhaust pipe 88 . Further, the fuel addition valve 29 may be arranged in the third exhaust pipe 88 downstream of the first exhaust temperature detection device 25 and upstream of the exhaust gas purification device 61 . .

Accordingly, the ECU 80 can improve the detection accuracy of the exhaust gas temperature TG flowing into the oxidation catalyst (DOC) 62 based on the detection signal from the first exhaust temperature detection device 25 . In addition, the unburned fuel added (injected) from the fuel addition valve 29 can smoothly flow into the oxidation catalyst (DOC) 62, and the efficiency of raising the temperature of the exhaust gas can be improved.

REFERENCE SIGNS LIST 1 exhaust purification system 6 intake flow rate detection device 10 engine 21 main turbocharger 22 sub turbocharger 25 first exhaust temperature detection device 29 fuel addition valve 46L first exhaust pipe 46R second exhaust pipe 61, 86 exhaust gas purification device 62 oxidation catalyst (DOC)
63 Filtered selective reduction catalyst (SCR-DPF)
65 differential pressure sensor 68 urea solution addition valve 80 ECU
87 Particulate matter removal filter (DPF)
88 Third exhaust pipe M11 Fuel addition limit map for single turbo mode M12 Fuel addition limit map for twin turbo mode

Claims (4)

an internal combustion engine having a primary turbocharger and a secondary turbocharger connected in parallel with the primary turbocharger;
a purification catalyst device disposed in an exhaust gas passage of the internal combustion engine, and oxidizing unburned fuel in the exhaust gas to raise the temperature of the exhaust gas and regenerate the particulate matter trapping function;
a fuel addition valve arranged upstream of the purification catalyst device in the exhaust gas passage and adding the unburned fuel to the exhaust gas;
a first exhaust gas temperature detection device arranged upstream of the purification catalyst device in the exhaust gas passage and detecting the temperature of inlet-side exhaust gas flowing into the purification catalyst device;
an exhaust gas flow rate acquisition device for acquiring an exhaust gas flow rate;
a supercharging state acquiring device for acquiring a supercharging state of the main turbocharger and the sub-turbocharger;
The inlet side exhaust gas temperature detected via the first exhaust temperature detection device, the exhaust gas flow rate obtained via the exhaust gas flow rate obtaining device, and the supercharging state obtaining device obtained via a limited addition amount calculation device for calculating a limited addition amount of fuel as an upper limit value of the addition amount per unit time of the unburned fuel added to the exhaust gas from the fuel addition valve, based on the supply state;
with
Exhaust purification system. In the exhaust purification system according to claim 1,
The supercharging state includes a single turbo mode in which only the main turbocharger is operated for supercharging, and a twin turbo mode in which the main turbocharger and the sub turbocharger are operated for supercharging,
The limit addition amount calculation device is
A single turbo mode map that is provided corresponding to the single turbo mode and is set such that the fuel limit addition amount decreases as the exhaust gas flow rate increases and increases as the inlet side exhaust gas temperature increases. and,
A map for twin turbo mode, which is provided corresponding to the twin turbo mode and is set such that the fuel limit addition amount decreases as the exhaust gas flow rate increases and increases as the inlet side exhaust gas temperature increases. and,
has
The limit addition amount calculation device is
When the supercharging state acquired via the supercharging state acquisition device is the single turbo mode, the inlet side exhaust gas temperature detected via the first exhaust temperature detection device and the exhaust gas flow rate The exhaust gas flow rate acquired via an acquisition device is collated with the single turbo mode map to calculate the fuel limit addition amount,
When the supercharging state acquired via the supercharging state acquisition device is the twin turbo mode, the inlet-side exhaust gas temperature detected via the first exhaust temperature detection device and the exhaust gas flow rate Computing the exhaust gas flow rate acquired via the acquisition device with the twin turbo mode map to calculate the limited fuel addition amount;
Exhaust purification system. In the exhaust purification system according to claim 1 or claim 2,
The purification catalyst device is
an oxidation catalyst carrying a precious metal that oxidizes the unburned fuel in the exhaust gas;
a filter-equipped selective reduction catalyst that is disposed downstream of the oxidation catalyst, collects the particulate matter, and selectively purifies NOx in the exhaust gas with a reducing agent solution of a predetermined concentration;
a reducing agent addition valve disposed downstream of the oxidation catalyst and upstream of the filtered selective reduction catalyst for adding the reducing agent solution to the exhaust gas;
has
a deposition amount acquisition device that acquires the deposition amount of the particulate matter collected by the selective reduction catalyst with filter;
a deposition amount determination device that determines whether or not the deposition amount of the particulate matter acquired via the deposition amount acquisition device has reached a predetermined deposition amount;
When it is determined by the deposition amount determination device that the deposition amount of the particulate matter has reached a predetermined deposition amount, the unburned fuel is added to the exhaust gas at a predetermined timing via the fuel addition valve. a reducing agent addition stop setting device that sets such that the reducing agent solution is not added to the exhaust gas from the reducing agent addition valve;
with
Exhaust purification system. In the exhaust purification system according to any one of claims 1 to 3,
a first exhaust pipe having one end connected to the outlet side of the main turbine of the main turbocharger and guiding exhaust gas to the inlet side of the catalyst purification device;
a second exhaust pipe having one end connected to the outlet side of the sub turbine of the sub turbocharger and the other end connected to the first exhaust pipe for guiding exhaust gas to the inlet side of the purification catalyst device;
with
The fuel addition valve and the first exhaust temperature detection device are arranged in the first exhaust pipe,
Exhaust purification system.

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