JP2005042604A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

In an exhaust gas purification system for an internal combustion engine, there is provided a technique capable of supplying air compressed by a supercharger as secondary air to an exhaust gas purification means while keeping the supercharging pressure constant at a required pressure.
SOLUTION: An exhaust purification means 14 provided in an exhaust passage 13 of an internal combustion engine 1, a supercharger 15 provided in an intake passage 9 of the internal combustion engine 1, a downstream of the supercharger 15 and the internal combustion engine 1. A communication pipe 25 that communicates the intake passage 9 upstream of the internal combustion engine 1 with the exhaust passage 13 downstream of the internal combustion engine 1 and upstream of the exhaust gas purification means 14, and a flow rate adjustment that adjusts the flow rate of the gas flowing through the communication pipe 25 And when the intake pressure is higher than the required pressure, the flow regulating valve 26 is opened to introduce air upstream of the exhaust purification means 14.
[Selection] Figure 1

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification system for an internal combustion engine that supplies secondary air into the exhaust gas of the internal combustion engine.
[0002]
[Prior art]
When air is supplied to the particulate filter, the oxidation of the particulate matter captured by the particulate filter can be promoted. Further, when air is supplied to the particulate filter or the exhaust purification catalyst, the temperature of the particulate filter or the like can be lowered, and overheating can be suppressed.
[0003]
For example, oil discharged from an oil pump is injected into a hydraulic turbine of a turbo rotating shaft to perform auxiliary driving of the turbocharger and supply a part of the supercharged air discharged from the turbocharger to the catalyst. A technique for suppressing overheating is known (see, for example, Patent Document 1). In addition, it has two superchargers for low and high rotation speeds, and when secondary air is needed, the start point for high rotation speeds is shifted to a higher rotation speed, resulting in a shortage of secondary air. (For example, refer to Patent Document 2), while operating the pressurizing pump at a predetermined supercharging pressure or higher and decelerating, pressurizes the air supercharged by the pressurizing pump and secondary air upstream of the catalyst (See, for example, Patent Document 3), reducing agent and secondary air are introduced from the turbocharger downstream to the catalyst upstream to promote atomization of the reducing agent, and the secondary air is supercharged when secondary air is unnecessary. A technique for storing air in a tank (for example, see Patent Document 4) is known.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-189720
[Patent Document 2]
JP-A-6-221172
[Patent Document 3]
JP-A-7-189716
[Patent Document 4]
JP-A-8-200047
[0005]
[Problems to be solved by the invention]
However, when air is supplied to the filter or the exhaust gas purification means using the supercharger as described above, it is necessary to provide a separate device to keep the supercharging pressure constant at the required pressure. In addition, a space for installing the apparatus is required. Even if the air from the supercharger is introduced into the exhaust system, the supercharging pressure is lowered, and the output of the internal combustion engine may be lowered.
[0006]
The present invention has been made in view of the above-described problems. In an exhaust gas purification system for an internal combustion engine, air compressed by a supercharger while maintaining a supercharging pressure constant at a required pressure is used as secondary air. It aims at providing the technique which can be supplied to an exhaust gas purification means.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention employs the following means. That is,
Exhaust purification means for purifying harmful components in the exhaust provided in the exhaust passage of the internal combustion engine;
A supercharger provided in an intake passage of the internal combustion engine for increasing the pressure of the intake air;
A communication pipe communicating with an intake passage downstream of the supercharger and upstream of the internal combustion engine and an exhaust passage downstream of the internal combustion engine and upstream of the exhaust gas purification means;
A flow rate adjusting valve for adjusting the flow rate of the gas flowing through the communication pipe;
With
When the pressure of the intake air raised by the supercharger becomes higher than the required pressure, the flow rate adjustment valve is opened to supply air to the exhaust passage upstream of the exhaust purification means. Features.
[0008]
The greatest feature of the present invention is that the boost pressure is kept constant at the required pressure by opening the flow rate adjusting valve only when the pressure of the intake air, that is, the supercharging pressure is equal to or higher than the required pressure. The air that sometimes flows out is to be supplied as secondary air to the exhaust gas purification means.
[0009]
Here, there is a required pressure (required pressure) for the supercharging pressure of the internal combustion engine, and the supercharging pressure is controlled to be the required pressure. The supercharging pressure can be controlled by discharging air in the intake passage and reducing the pressure in the intake passage when the supercharging pressure becomes higher than the required pressure. As a result, the supercharging pressure can be kept constant at the required pressure. Further, by supplying the air discharged at this time to the exhaust passage upstream of the exhaust purification means, it becomes possible to supply air to the exhaust purification means. In other words, it is possible to introduce excess air into the exhaust passage while leaving the air necessary for keeping the supercharging pressure constant at the required pressure in the intake passage. The air thus supplied to the exhaust passage is supplied as secondary air to the exhaust purification means.
[0010]
In the present invention, the supercharger is a variable capacity turbocharger in which the flow rate of the exhaust gas blown to the turbine wheel is made variable by opening and closing the nozzle vanes so that the intake pressure becomes a desired pressure.
When the pressure of the intake air raised by the supercharger is lower than the required pressure and when air is supplied to the exhaust passage upstream of the exhaust purification means, the nozzle vane is controlled to the closed side. Thus, the intake pressure can be increased to the required pressure.
[0011]
When the supercharging pressure is lower than the required pressure, if the flow regulating valve is opened and air is introduced into the exhaust passage, the supercharging pressure is further reduced and the output of the internal combustion engine is reduced. Therefore, in such a case, the supercharging pressure can be increased to the required pressure by controlling the nozzle vane to the closing side, that is, the side to increase the supercharging pressure. And it becomes possible to supply surplus air to the exhaust passage.
[0012]
In the present invention, the exhaust gas purification means includes a particulate filter capable of temporarily capturing particulate matter contained in the exhaust gas, and the flow rate adjustment is performed when the particulate matter captured by the particulate filter is oxidized and removed. Air can be supplied to the exhaust passage by opening the valve.
[0013]
Since the air supplied to the exhaust passage through the communication pipe contains a lot of oxygen, when introduced into the particulate filter, it is possible to promote the oxidation of the particulate matter captured by the particulate filter by the oxygen. Become.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
A specific embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, a case where the exhaust gas purification system for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
[0015]
FIG. 1 is a diagram showing a schematic configuration of an engine and its intake / exhaust system according to the present embodiment.
[0016]
An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0017]
The engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 that accumulates fuel to a predetermined pressure.
[0018]
The common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5. This fuel pump 6 is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source, and a crank pulley in which a pump pulley 6a attached to the input shaft of the fuel pump 6 is attached to the crankshaft. 1a and belt 7 are connected. The fuel pump 6 discharges fuel at a pressure corresponding to the rotational torque transmitted from the crankshaft to the input shaft of the fuel pump 6.
[0019]
In addition, an intake branch pipe 8 is connected to the engine 1, and each branch pipe of the intake branch pipe 8 leads to a combustion chamber of each cylinder 2.
[0020]
The intake branch pipe 8 is connected to an intake pipe 9, and a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using exhaust energy as a drive source is provided in the middle of the intake pipe 9. .
[0021]
An intake throttle valve 10 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 10 is provided with an intake throttle actuator 11 that is configured by a step motor or the like and that opens and closes the intake throttle valve 10.
[0022]
The intake branch pipe 8 is provided with a pressure sensor 22 that outputs a signal corresponding to the pressure in the intake branch pipe 8 and can measure the pressure in the intake branch pipe 8. The pressure sensor 22 measures the supercharging pressure.
[0023]
In the intake system configured as described above, the intake air flows into the compressor housing 15 a via the intake pipe 9. The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a, and then flows into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chambers of the respective cylinders 2 through the respective branch pipes, and is burned using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0024]
On the other hand, an exhaust branch pipe 12 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 12 communicates with a combustion chamber of each cylinder 2 via an exhaust port 1b.
[0025]
The exhaust branch pipe 12 is connected to a turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15 b is connected to the exhaust pipe 13.
[0026]
A particulate filter (hereinafter simply referred to as a filter) 14 carrying an NOx storage reduction catalyst is provided in the middle of the exhaust pipe 13. The filter 14 captures particulate matter (hereinafter referred to as PM) in the exhaust gas, stores NOx in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and decreases the oxygen concentration of the inflowing exhaust gas. When a reducing agent is present, it has a function of reducing stored NOx.
[0027]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 12 through the exhaust port 1 b and flows into the filter 14. The filter 14 captures PM in the exhaust gas, stores NOx, and purifies the exhaust gas.
[0028]
The intake pipe 9 downstream of the compressor housing 15a and upstream of the intake throttle valve 10 and the exhaust pipe 13 downstream of the turbine housing 15b and upstream of the filter 14 are compressed by the turbocharger 15 and compressed into the intake pipe 9. A part of the air flowing inside (hereinafter referred to as supercharged air) is communicated by a communication pipe 25 that introduces a part of the air into the exhaust pipe 13. In the middle of the communication pipe 25, there is provided a flow rate adjusting valve 26 which is constituted by an electromagnetic valve or the like and changes the flow rate of supercharged air flowing through the communication pipe 25 in accordance with the magnitude of applied power. This flow rate adjustment valve 26 can be selected only in either the fully open state or the fully closed state, and by adjusting the time for the fully open or fully closed state, the supercharged air flowing through the communication pipe 25 can be adjusted. The flow rate can be adjusted. The flow rate adjusting valve 26 may be capable of maintaining the valve at an arbitrary opening degree.
[0029]
In the secondary air introduction mechanism configured as described above, when the flow rate adjustment valve 26 is opened, the intake system and the exhaust system are communicated with each other through the communication pipe 25. At this time, if the pressure in the intake system is higher than that in the exhaust system, a part of the air flowing through the intake pipe 9 flows into the communication pipe 25 and is introduced into the exhaust pipe 13. The air introduced into the exhaust pipe 13 flows into the filter 14 while being mixed with the exhaust flowing from the upstream of the exhaust pipe 13.
[0030]
The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 27 for controlling the engine 1. The ECU 27 is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.
[0031]
Various sensors are connected to the ECU 27 via electric wiring, and in addition to the output signals of the various sensors described above, an electric signal corresponding to the rotational position of the crankshaft is output to enable measurement of the engine speed. 23, an electric signal corresponding to the amount of depression of the accelerator by the driver is output, and an output signal of the accelerator opening sensor 24 that enables measurement of the engine load is input.
[0032]
On the other hand, the fuel injection valve 3, the intake throttle actuator 11, the flow rate adjustment valve 26, and the like are connected to the ECU 27 via electrical wiring, and these can be controlled. The ECU 27 stores various application programs and various control maps.
[0033]
By the way, when PM captured by the filter 14 accumulates on the filter 14, the filter may be clogged. If this clogging occurs, the pressure of the exhaust gas upstream of the filter 14 may increase, which may cause a reduction in the output of the engine 1 or damage to the filter 14. In such a case, the PM deposited on the filter 14 can be oxidized to be removed. The removal of PM deposited on the filter in this way is called filter regeneration.
[0034]
This filter can be regenerated by placing the filter 14 in a high temperature state and an oxygen-excess atmosphere. Here, a technique for supplying secondary air from upstream of the filter 14 in order to promote oxidation of PM is known.
[0035]
On the other hand, when the temperature of the filter 14 becomes excessively high, damage to the filter 14 and thermal deterioration of the NOx catalyst carried on the filter 14 are induced. Here, when the temperature of the filter 14 becomes excessively high, the temperature of the filter 14 can be lowered by circulating the secondary air through the filter 14.
[0036]
By the way, in order to supply the secondary air to the exhaust passage, conventionally, a pump for pumping the air has been separately required. For this reason, the cost is high, and it may be difficult to secure a space for mounting the pump. In addition, it is conceivable that air whose pressure has been increased by the supercharger is introduced from the intake passage to the exhaust passage, but it is also conceivable that the supercharging pressure is lowered and the output of the engine is lowered.
[0037]
In this regard, in the present embodiment, the excess air compressed and compressed by the turbocharger 15 is disposed upstream of the filter 14 while ensuring the supercharging pressure and intake air amount necessary to generate the required output. Supply to the exhaust pipe 13. That is, the secondary air is supplied within a range in which the supercharging pressure is not reduced, and the regeneration of the filter 14 and the temperature adjustment can be performed while suppressing the output reduction of the engine 1.
[0038]
For example, the supercharging pressure is measured by the pressure sensor 22, and when the measured value is equal to or higher than the required pressure, the flow regulating valve 26 is opened.
[0039]
Next, the flow of secondary air supply control according to the present embodiment will be described.
[0040]
Here, FIG. 2 is a flowchart showing a flow of secondary air supply control according to the present embodiment.
[0041]
In step S101, it is determined whether the filter 14 requires secondary air.
[0042]
For example, the determination is made based on whether or not PM has accumulated so that the filter 14 needs to be regenerated. As for the amount of PM accumulated in the filter 14, for example, a differential pressure sensor for detecting the differential pressure before and after the filter 14 is attached to the exhaust pipe 13, and the PM amount corresponding to the detection value of the differential pressure sensor is previously tested. It can be obtained by obtaining in advance. Further, the PM trapping amount corresponding to the operating state of the engine 1 (exhaust temperature, fuel injection amount, engine speed) is obtained in advance by experiments and mapped, and the PM trapping amount obtained from this map is integrated to obtain PM. It can also be set as the accumulation amount of. Furthermore, the PM accumulation amount may be estimated according to the vehicle travel distance or travel time. Then, when the PM accumulation amount reaches a predetermined allowable amount, it is determined that secondary air is required.
[0043]
Alternatively, the determination may be made based on whether or not the temperature of the filter 14 needs to be lowered. The temperature of the filter 14 may be measured by attaching a temperature sensor downstream of the filter 14. Moreover, you may estimate from the log | history of the driving | running state (fuel injection amount, engine speed) of the engine 1. FIG. Then, when the temperature of the filter 14 reaches a predetermined allowable temperature, it is determined that secondary air is required.
[0044]
If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this routine is terminated.
[0045]
In step S102, a process for increasing the supercharging pressure is performed.
[0046]
Here, if the supercharging pressure has reached the required pressure, excess air can be supplied to the exhaust pipe 13. However, if the required pressure has not been reached, the supercharging pressure will decrease. Air cannot be supplied to the exhaust pipe 13.
[0047]
Therefore, when the supercharging pressure does not reach the required pressure, for example, the amount of air taken into the engine is increased or the temperature of the exhaust gas is increased so that the supercharging pressure rises quickly.
[0048]
As a method for increasing the amount of air, for example, in the case of an internal combustion engine having an automatic transmission, it is possible to shift to a low speed gear, or to control the EGR valve to the closed side and the intake throttle valve to the open side. When the amount of air increases in this way, the amount of exhaust gas increases accordingly, and the rotational speed of the turbine wheel increases. Thereby, a supercharging pressure can be raised rapidly.
[0049]
Further, as a method for increasing the temperature of the exhaust, sub-injection in which fuel is injected again during the expansion stroke or the exhaust stroke after the main injection from the fuel injection valve 3 in the engine 1 can be exemplified. The reason why the fuel is injected again after the main fuel for the engine output is injected into the cylinder 2 of the engine 1 in this way is that when the main injection is increased, the combustion of the fuel becomes the engine output, so that torque fluctuation occurs. This is because the driving state may be deteriorated.
[0050]
Further, the exhaust gas temperature can be increased by delaying the fuel injection timing into the cylinder 2. When the fuel injection timing is delayed from the normal time, the amount of energy consumed for the movement of the piston is smaller than the fuel injected at the normal time. Thereby, the temperature of exhaust can be raised. Thus, when the temperature of the exhaust gas rises, the volume of the exhaust gas expands, and accordingly, the amount of exhaust gas increases and the rotation speed of the turbine wheel increases. Thereby, a supercharging pressure can be raised.
[0051]
In this way, it is possible to increase the supercharging pressure by increasing the engine speed or increasing the temperature of the exhaust to increase the amount of air discharged from the turbocharger 15. As a result, the operating range of the engine 1 that can supply the secondary air to the filter 14 can be expanded.
[0052]
Further, in a general turbocharger 15, when the required pressure is reached, the exhaust gas flowing into the turbine housing 15b inlet is diverted to the turbine housing 15b outlet so that the supercharging pressure does not increase excessively. In the present embodiment, such detouring is not performed, and instead, supercharging air may be introduced into the exhaust pipe 13 so that the supercharging pressure does not increase excessively.
[0053]
In step S103, it is determined whether or not the supercharging pressure is equal to or higher than the required pressure. The supercharging pressure is measured by the pressure sensor 22. The required pressure can be obtained from a map obtained by previously determining the relationship between the operating state (the number of revolutions and the load) of the engine 1 and the required pressure by experiments or the like.
[0054]
If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process returns to step S102.
[0055]
In step S104, secondary air is introduced into the filter 14 to promote PM oxidation and to lower the temperature.
[0056]
That is, the flow rate adjustment valve 26 is opened, and the supercharged air is introduced into the exhaust pipe 13. Here, feedback control of the opening and closing of the flow rate adjustment valve 26 is performed so that the supercharging pressure obtained by the pressure sensor 22 becomes the required pressure. That is, when the supercharging pressure is higher than the required pressure, it is fully opened, and when it is low, it is fully closed. In addition, when the flow rate adjustment valve 26 is a valve that can be maintained at an arbitrary opening degree, the valve opening degree may be feedback-controlled so that the required pressure is obtained.
[0057]
At this time, the amount of air supplied may be adjusted according to the temperature of the filter 14. That is, when the temperature of the filter 14 is to be increased, the opening time of the flow rate adjusting valve 26 is shortened so that the supply amount of the secondary air is reduced, while when the temperature of the filter 14 is to be decreased. The valve opening time of the flow rate adjustment valve 26 may be lengthened.
[0058]
When the engine load increases, the exhaust pressure increases and the amount of air introduced into the exhaust pipe 13 decreases. Therefore, in such an operating state, the secondary air may not be introduced. In addition, in the idling state or a low load operation region close to the idling state, it is difficult to increase the supercharging pressure, and therefore secondary air may not be introduced. In addition, in the operation state where it is difficult to increase the supercharging pressure, the secondary air may not be introduced. Further, the exhaust pressure may be measured, and the flow rate adjusting valve 26 may be opened only when the intake pressure is higher than the exhaust pressure.
[0059]
In the present embodiment, a filter carrying a NOx catalyst as an exhaust purification means has been described as an example. However, instead of this, temperature adjustment can be performed even with a simple NOx catalyst, an oxidation catalyst, or a three-way catalyst. it can. Even a simple filter that does not carry a NOx catalyst can promote PM oxidation.
[0060]
In the present embodiment, the example applied to the promotion of the oxidation of PM and the temperature adjustment of the filter has been described. However, the present embodiment can be applied to the adjustment of the air-fuel ratio in the ambient atmosphere of the filter and the catalyst instead. it can. For example, the air-fuel ratio in the atmosphere surrounding the filter and catalyst is measured by a sensor, and when this value is lower than the target air-fuel ratio, the flow rate adjustment valve 26 is opened to increase the air-fuel ratio. In this way, the air-fuel ratio of the exhaust can be controlled.
[0061]
As described above, according to the present embodiment, the pressure of the intake air can be maintained at the required pressure, so that a decrease in engine output can be suppressed, and secondary air is supplied to the filter 14. Therefore, the oxidation of PM deposited on the filter 14 can be promoted and the temperature of the filter 14 can be controlled. Further, it is not necessary to separately provide a pump for sending air to the filter 14.
[0062]
<Second Embodiment>
This embodiment is different from the first embodiment in the following points. That is, in the present embodiment, a variable capacity turbocharger is employed for the supercharger.
[0063]
Note that the basic configuration of the engine 1 and other hardware to be applied is the same as that of the first embodiment, and thus description thereof is omitted.
[0064]
FIG. 3 is a cross-sectional view showing the configuration of the variable capacity turbocharger. 3A shows a case where the nozzle vane 51 is open, and FIG. 3B shows a case where the nozzle vane 51 is closed.
[0065]
As shown in the figure, the variable displacement turbocharger 15 is configured to include a plurality of nozzle vanes 51 around the turbine wheel 50 in the turbine housing 15b. The nozzle vane 51 is opened and closed by an actuator 52.
[0066]
When the nozzle vane 51 is rotated to the closing side, the gap between the adjacent nozzle vanes 51 is narrowed, and the flow path between the nozzle vanes 51 is closed.
[0067]
On the other hand, when the nozzle vane 51 is rotated to the opening side, the gap between the adjacent nozzle vanes 51 is widened, and the flow path between the nozzle vanes 51 is opened.
[0068]
In the variable capacity turbocharger 15 configured as described above, the direction of the flow path between the nozzle vanes 51 and the gap between the nozzle vanes 51 are changed by adjusting the rotation direction and the rotation amount of the nozzle vanes 51 by the actuator 52. It becomes possible to do. That is, by controlling the rotation direction and the rotation amount of the nozzle vane 51, the direction and flow velocity of the exhaust blown to the turbine wheel 50 are adjusted.
[0069]
For example, when the amount of exhaust from the engine 1 is small, by operating the actuator 52 to close the nozzle vane 51, the flow velocity of the exhaust blown to the turbine wheel 50 is increased, and the rotational speed of the turbine wheel 50 is reduced even with a small amount of exhaust. In addition, the rotational force can be increased.
[0070]
On the other hand, when the amount of exhaust from the engine 1 is sufficiently large, by operating the actuator 52 to open the nozzle vane 51, an excessive increase in the flow velocity of the exhaust blown to the turbine wheel 50 is controlled. It is possible to suppress an excessive increase in rotational speed and rotational force.
[0071]
In the exhaust gas purification system for an internal combustion engine having such a variable displacement turbocharger 15, when it is necessary to supply secondary air to the filter 14 and the supercharging pressure is lower than the required pressure, The nozzle vane 51 is controlled to the closing side. Thereby, the flow velocity of the exhaust gas blown to the turbine wheel 50 is increased, and the rotational speed and the rotational force of the turbine wheel 50 can be increased even with a small amount of exhaust gas. Thereby, a supercharging pressure can be raised to a required pressure.
[0072]
Here, FIG. 4 shows the time transition of the secondary air supply request, the nozzle vane opening, the intake branch pipe pressure, the flow regulating valve opening signal, the intake air amount, and the secondary air supply amount according to the present embodiment. It is a time chart figure.
[0073]
The “secondary air supply request” is turned ON when the supply of secondary air is necessary for promoting oxidation of PM or adjusting the temperature of the filter 14, and turned OFF otherwise.
[0074]
The “intake branch pipe pressure” is an output signal from the pressure sensor 22. Here, the alternate long and short dash line indicates a case where the flow rate adjustment valve is maintained in a closed state.
[0075]
The “flow rate adjustment valve opening signal” indicates a signal for opening and closing the flow rate adjustment valve 26. The flow rate adjustment valve 26 is opened when the flow rate adjustment valve 26 is ON, and is closed when it is OFF.
[0076]
The “intake air amount” indicates the amount of air sucked into the cylinder 2.
[0077]
The “secondary air supply amount” indicates the amount of secondary air that passes through the communication pipe 25 and is supplied to the exhaust pipe 13.
[0078]
Here, when the oxidation of PM and the temperature adjustment of the filter 14 are necessary, the secondary air supply request is turned ON. The nozzle vane 51 is controlled to the open side so that the supercharging pressure, that is, the pressure in the intake branch pipe does not decrease. At the same time, the flow regulating valve opening signal is repeatedly turned ON and OFF, and the intake branch pipe pressure (supercharging pressure) is kept constant at the required pressure. Here, the flow regulating valve opening signal is turned on when the supercharging pressure is higher than the required pressure, and turned off when the boost pressure is lower. As a result, the supercharging pressure and the intake air amount are maintained constant, and the secondary air supply amount can be further increased. Note that these controls replace step S102 in FIG. 2 in the first embodiment.
[0079]
As described above, according to the present embodiment, the pressure of the intake air can be maintained at the required pressure, so that a decrease in engine output can be suppressed, and secondary air is supplied to the filter 14. Therefore, the oxidation of PM deposited on the filter 14 can be promoted and the temperature of the filter 14 can be controlled. Further, it is not necessary to separately provide a pump for sending air to the filter 14. Further, by providing the variable displacement turbocharger 15, the supercharging pressure can be easily increased, and therefore secondary air can be easily supplied to the filter 14. In addition, the operating range of the engine 1 capable of supplying secondary air can be expanded.
[0080]
<Third Embodiment>
This embodiment is different from the first embodiment in the following points. In other words, in the present embodiment, a mechanically driven supercharger (hereinafter simply referred to as a supercharger) is adopted as the supercharger.
[0081]
Note that the basic configuration of the engine 1 and other hardware to be applied is the same as that of the first embodiment, and thus description thereof is omitted.
[0082]
FIG. 5 is a diagram showing a schematic configuration of the engine and its intake / exhaust system according to the present embodiment.
[0083]
In the present embodiment, a supercharger 30 is provided in the middle of the intake pipe 9. The supercharger 30 is a supercharger that operates using the rotational torque of the crankshaft as a drive source. A pulley 30 a attached to the input shaft of the supercharger 30 is connected to a crank pulley 1 a attached to the crankshaft of the engine 1. It is connected via a belt 7.
[0084]
In the intake system configured as described above, air having a pressure corresponding to the rotational torque transmitted from the crankshaft to the input shaft of the supercharger 30 is discharged to the intake pipe 9. The pressure in the intake pipe 9 and the intake branch pipe 8 rises due to the air discharged from the supercharger 30.
[0085]
Here, in the general supercharger, since it is connected to the crankshaft by the belt 7, the ratio between the rotation speed of the engine 1 and the rotation speed of the supercharger (hereinafter simply referred to as the rotation ratio) is always equal. That is, the rotational speed of the supercharger is determined according to the rotational speed of the engine. Therefore, even if the supercharging pressure is lowered, it is not possible to increase only the rotation speed of the supercharger.
[0086]
Therefore, in the present embodiment, the rotation ratio is set so that the supercharged air can be supplied into the exhaust pipe 13 while keeping the supercharging pressure in the intake branch pipe 8 constant at the required pressure. That is, even if air is supplied into the exhaust pipe 13, the rotation speed of the supercharger 30 is set to be high in advance so that the supercharging pressure can maintain the required pressure. For example, this can be achieved by reducing the diameter of the pulley 30a. As a result, the boost pressure can be quickly increased, and surplus boost air can be supplied to the exhaust pipe 13 as secondary air. Further, for example, an electromagnetic clutch or the like that can change the rotation ratio may be provided between the pulley 30a and the main body of the supercharger 30. In this way, the amount of air discharged from the supercharger 30 can be increased only when the secondary air needs to be supplied to the filter 14.
[0087]
Further, a gear or the like may be provided on the input shaft of the supercharger 30 so that the rotation ratio can be changed, and the rotation speed of the supercharger 30 may be increased when supplying secondary air.
[0088]
As described above, in the supercharger 30 that includes an electromagnetic clutch, a gear, and the like and can change the supercharging pressure, the supercharging pressure may be set so as to realize a pressure higher than the required supercharging pressure.
[0089]
In this way, it is possible to supply excess supercharged air to the exhaust pipe 13 while maintaining the supercharging pressure required by the engine.
[0090]
Note that these controls replace step S102 in FIG. 2 in the first embodiment.
[0091]
<Other embodiments>
In the first to third embodiments, surplus air in the intake pipe 9 is supplied to the filter 14 and used for promoting oxidation of PM and adjusting the temperature of the filter 14.
[0092]
In this respect, in the present embodiment, air from the supercharger is injected together with fuel. This fuel may be a fuel injected from the fuel injection valve 3 or a fuel injected into the exhaust system for reduction of NOx stored in the NOx catalyst.
[0093]
Here, there is known a fuel injection valve that injects fuel and pressurized air while mixing them. Thus, fuel atomization can be promoted by mixing and injecting fuel and air. And conventionally, a pump for pressurizing the air injected at this time has been provided. However, the provision of a pump increases the cost, and it is also necessary to secure a space for mounting the pump.
[0094]
On the other hand, if the excess air in the intake pipe 9 is used, the excess air can be injected together with the fuel while keeping the supercharging pressure constant at the required pressure, and there is no need to provide a separate pump.
[0095]
【The invention's effect】
In the exhaust gas purification system for an internal combustion engine according to the present invention, high-pressure air can be supplied to the exhaust passage upstream of the exhaust gas purification means while maintaining the required supercharging pressure. Thereby, the oxidation of the particulate matter captured by the exhaust gas purification means can be promoted. In addition, the temperature of the exhaust purification means can be adjusted.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an engine and its intake / exhaust system according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a flow of secondary air supply control according to the embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a configuration of a variable capacity turbocharger. FIG. 3A shows a case where the nozzle vane is open, and FIG. 3B shows a case where the nozzle vane is closed.
FIG. 4 is a time chart showing the time transition of secondary air supply request, nozzle vane opening, intake branch pipe pressure, flow regulating valve opening signal, intake air amount, and secondary air supply amount according to the second embodiment. It is a chart figure.
FIG. 5 is a diagram showing a schematic configuration of an engine and its intake / exhaust system according to a third embodiment.
[Explanation of symbols]
1 engine
1a Crank pulley
1b Exhaust port
2-cylinder
3 Fuel injection valve
4 Common rail
5 Fuel supply pipe
6 Fuel pump
6a Pump pulley
7 Belt
8 Intake branch pipe
9 Intake pipe
10 Inlet throttle valve
11 Inlet throttle actuator
12 Exhaust branch pipe
13 Exhaust pipe
14 Particulate filter
15 Turbocharger
15a Compressor housing
15b Turbine housing
22 Pressure sensor
23 Crank position sensor
24 accelerator position sensor
25 communication pipe
26 Flow control valve
27 ECU
30 Supercharger
30a pulley
50 Turbine wheel
51 Nozzle vanes
52 Actuator

Claims (3)

Exhaust purification means for purifying harmful components in the exhaust provided in the exhaust passage of the internal combustion engine;
A supercharger provided in an intake passage of the internal combustion engine for increasing the pressure of the intake air;
A communication pipe communicating with an intake passage downstream of the supercharger and upstream of the internal combustion engine and an exhaust passage downstream of the internal combustion engine and upstream of the exhaust gas purification means;
A flow rate adjusting valve for adjusting the flow rate of the gas flowing through the communication pipe;
With
When the pressure of the intake air raised by the supercharger becomes higher than the required pressure, the flow rate adjustment valve is opened to supply air to the exhaust passage upstream of the exhaust purification means. An exhaust gas purification system for an internal combustion engine. The supercharger is a variable capacity turbocharger in which the flow rate of exhaust gas blown to the turbine wheel to change the intake pressure to a desired pressure is variable by opening and closing nozzle vanes,
When the pressure of the intake air raised by the supercharger is lower than the required pressure and when air is supplied to the exhaust passage upstream of the exhaust purification means, the nozzle vane is controlled to the closed side. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the pressure of the intake air is increased to a required pressure. The exhaust purification means comprises a particulate filter capable of temporarily capturing particulate matter contained in the exhaust, and when the particulate matter captured by the particulate filter is oxidized and removed, the flow control valve is opened. 3. An exhaust gas purification system for an internal combustion engine according to claim 1, wherein air is supplied to the exhaust passage.

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