JP4858023B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine provided with a supercharger that makes a supercharging pressure variable.

  In an exhaust gas purification system for an internal combustion engine, a reducing agent may be supplied to the exhaust gas purification device in order to recover the performance of an exhaust gas purification device (such as an NOx storage reduction catalyst or a particulate filter) provided in the exhaust passage. .

  As described above, when the reducing agent is supplied to the exhaust purification device, if the flow rate of the exhaust gas is large, the time for the supplied reducing agent to pass through the exhaust purification device is shortened, so that the performance of the exhaust purification device can be recovered. It becomes difficult to use the reducing agent for chemical reaction. As a result, the efficiency of performance recovery may be reduced, or the amount of reducing agent that may pass through the exhaust purification device may increase.

  Therefore, a technique is known in which an exhaust throttle valve is provided in the exhaust passage and the exhaust throttle valve is controlled in the closing direction when the flow rate of the exhaust gas is large when supplying the reducing agent to the exhaust purification device. When the exhaust throttle valve is controlled in the valve closing direction, the flow rate of the exhaust gas can be suppressed, so that the time for the reducing agent to pass through the exhaust gas purification device can be lengthened. Accordingly, the reducing agent is easily used in a chemical reaction for recovering the performance of the exhaust purification device in the exhaust purification device.

Patent Document 1 discloses a technique for increasing the opening of the exhaust throttle valve when supplying the additive substance to the NOx absorbent provided in the exhaust passage when the intake air amount is small compared to when the intake air amount is large. Yes.
Japanese Patent No. 3695378 JP-A-10-306717

  When supplying a reducing agent to the exhaust gas purification device to restore the performance of the exhaust gas purification device, if the exhaust throttle valve is controlled in the valve closing direction due to the large flow rate of the exhaust gas, the back pressure increases and the pump loss in the internal combustion engine increases. May increase. When the pump loss in the internal combustion engine increases, the fuel consumption may deteriorate.

  It is an object of the present invention to provide a technique capable of suppressing an excessive increase in pump loss in an internal combustion engine when a reducing agent is supplied to the exhaust purification device so as to restore the performance of the exhaust purification device. .

  The present invention controls the exhaust throttle valve in the valve closing direction and reduces the supercharging pressure by the supercharger when the flow rate of the exhaust gas is large when supplying the reducing agent to the exhaust gas purification device.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
A turbocharger with variable supercharging pressure;
An exhaust purification device provided in the exhaust passage;
Reducing agent supply means for supplying a reducing agent to the exhaust gas purification device in order to restore the performance of the exhaust gas purification device;
An exhaust throttle valve provided in the exhaust passage for controlling the flow rate of the exhaust;
An exhaust throttle valve control for controlling the exhaust throttle valve in a valve closing direction when the flow rate of the exhaust gas flowing through the exhaust passage is greater than or equal to a predetermined flow rate when the reducing agent is supplied to the exhaust gas purification device by the reducing agent supply means. Means, and
When the reducing agent is supplied to the exhaust gas purification device by the reducing agent supply means, when the back pressure when the exhaust throttle valve control means controls the exhaust throttle valve in the valve closing direction is a predetermined pressure or more, The supercharging pressure by the supercharger is reduced.

  Here, the predetermined flow rate is within an allowable range of the amount of reducing agent that is not used for a chemical reaction for restoring the performance of the exhaust purification device because the time during which the supplied reducing agent passes through the exhaust purification device becomes excessively short. It is a threshold value of the exhaust gas flow rate that can be determined to be larger than the above.

  The predetermined pressure is a back pressure threshold at which it can be determined that the pump loss in the internal combustion engine increases excessively.

  When the supercharging pressure by the supercharger is reduced, the intake air amount is reduced, so that the flow rate of the exhaust gas can be reduced. Therefore, it is possible to suppress an increase in back pressure when the exhaust throttle valve is controlled in the valve closing direction.

  Therefore, according to the present invention, it is possible to suppress an excessive increase in pump loss in the internal combustion engine when the reducing agent is supplied to the exhaust purification device so as to restore the performance of the exhaust purification device.

  In the present invention, the turbocharger may be a turbocharger having a turbine provided upstream of the exhaust gas purification device in the exhaust passage. In this case, when the reducing agent is supplied to the exhaust purification device by the reducing agent supply means, the back pressure when the exhaust throttle valve is controlled in the valve closing direction by the exhaust throttle valve control means is lower than the predetermined pressure. In addition, when the temperature of the exhaust gas flowing into the exhaust gas purification device is equal to or lower than a predetermined temperature, the supercharging pressure by the turbocharger may be reduced.

  Here, the predetermined temperature is a threshold value of the exhaust gas temperature at which it can be determined that the reducing agent is hardly used for a chemical reaction for recovering the performance of the exhaust gas purification apparatus.

  By reducing the supercharging pressure by the turbocharger, the energy of the exhaust gas used for supercharging by the turbocharger can be reduced. As a result, the temperature drop of the exhaust gas in the turbine can be suppressed.

  Therefore, according to the above, the temperature of the exhaust gas flowing into the exhaust purification device can be further increased. Thereby, the chemical reaction for recovering the performance of the exhaust emission control device can be further promoted.

  According to the present invention, it is possible to suppress an excessive increase in pump loss in an internal combustion engine when supplying a reducing agent to the exhaust purification device so as to restore the performance of the exhaust purification device.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 for directly injecting fuel into the cylinder 2.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. One end of an intake passage 4 is connected to the intake manifold 5. One end of an exhaust passage 6 is connected to the exhaust manifold 7. In this embodiment, the exhaust passage 6 is connected to a position in the vicinity of the fourth cylinder of the exhaust manifold 7.

  A compressor 8 a of a turbocharger (supercharger) 8 is installed in the intake passage 4. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 6.

  The turbocharger 8 according to the present embodiment is a turbocharger with variable supercharging pressure. Here, a schematic configuration of the turbocharger 8 according to the present embodiment will be described with reference to FIG. A center housing 8c is provided between the compressor 8a and the turbine 8b in the turbocharger 8. A rotor shaft 16 is supported on the center housing 8c so as to be rotatable about its axis.

  At one end of the rotor shaft 16, a compressor wheel 14 installed in the compressor 8a is attached. A turbine wheel 15 installed in the turbine 8 b is attached to the other end of the rotor shaft 16.

  In the turbocharger 8 having such a configuration, the turbine wheel 15 rotates when the exhaust is blown, and the compressor wheel 14 rotates when the turbine wheel 15 rotates. Then, so-called supercharging is performed by increasing the amount of air fed into the intake passage 4 on the downstream side of the compressor 8 a by the rotation of the compressor wheel 14.

  Further, in the turbine 8 b, a plurality of blade-shaped nozzle vanes 17 are attached in the circumferential direction of the turbine wheel 15. Further, the turbine 8b is provided with an actuator 13 that drives the nozzle vane 17 to open and close. When the nozzle vane 17 is driven to open and close by the actuator 13, the size of the gap between the adjacent nozzle vanes 17 changes. Therefore, the flow rate of the exhaust gas blown to the turbine wheel 15 changes, and as a result, the rotation speed of the compressor wheel 14 changes. This makes it possible to adjust the supercharging pressure to the intake passage 2 downstream from the compressor 8a.

  An air flow meter 12 is provided upstream of the compressor 8 a in the intake passage 4. Further, a particulate filter (hereinafter simply referred to as a filter) 9 that collects particulate matter (hereinafter referred to as PM) in the exhaust gas is provided on the downstream side of the turbine 8 b in the exhaust passage 6. Yes. The filter 9 carries an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst). In the present embodiment, the filter 9 carrying the NOx catalyst corresponds to the exhaust purification device according to the present invention.

  Further, a temperature sensor 18 that detects the temperature of the exhaust gas is provided in the exhaust passage 6 downstream of the turbine 8 b and upstream of the filter 9. Further, an exhaust throttle valve 10 for controlling the flow rate of exhaust gas is provided downstream of the filter 9 in the exhaust passage 6. A fuel addition valve 11 for adding fuel as a reducing agent in the exhaust gas is installed in the exhaust manifold 7 in the vicinity of the connection portion of the exhaust passage 6. In this embodiment, the fuel addition valve 11 corresponds to the reducing agent supply means according to the present invention.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 20. The ECU 20 is a unit that controls the operating state of the internal combustion engine 1. An air flow meter 12 and a temperature sensor 18 are electrically connected to the ECU 20. These output signals are input to the ECU 20. The ECU 20 estimates the flow rate of the exhaust gas in the exhaust passage 6 based on the detection value of the air flow meter 12.

  Further, the fuel injection valve 3 and the actuator 13, the exhaust throttle valve 10, and the fuel addition valve 11 are electrically connected to the ECU 20. These are controlled by the ECU 20.

<Filter regeneration control>
Here, filter regeneration control for removing PM collected by the filter 9 will be described. The filter regeneration control according to this embodiment is performed by adding fuel from the fuel addition valve 11. The fuel added from the fuel addition valve 11 flows into the filter 9 together with the exhaust gas, and is oxidized by the NOx catalyst carried on the filter 9. The filter 9 is heated by the oxidation heat at this time, and as a result, PM is oxidized and removed.

  If the flow rate of the exhaust gas is large when such filter regeneration control is executed, the time for the fuel added from the fuel addition valve 11 to pass through the filter 9, that is, the time to pass through the NOx catalyst, becomes short. For this reason, the fuel is hardly oxidized in the NOx catalyst. As a result, the temperature of the filter 9 is difficult to increase, and the PM removal efficiency may be reduced. Further, the amount of fuel that passes through the filter 9 without being oxidized by the NOx catalyst and is released to the outside may increase.

  Therefore, in this embodiment, when the flow rate of the exhaust gas is equal to or higher than the predetermined flow rate when the filter regeneration control is executed, the fuel is added from the fuel addition valve 11 and the exhaust throttle valve 10 is closed. Here, the predetermined flow rate is an exhaust gas that can be determined that the amount of fuel that is not oxidized in the NOx catalyst exceeds the allowable range because the time that the fuel added from the fuel addition valve 11 passes through the filter 9 is excessively short. This is the flow rate threshold.

  When the exhaust throttle valve 10 is closed, the flow rate of the exhaust gas flowing through the filter 9 can be suppressed. Therefore, the time for the fuel added from the fuel addition valve 11 to pass through the filter 9 can be lengthened. Therefore, it is possible to promote fuel oxidation in the NOx catalyst.

  However, if the exhaust throttle valve 10 is closed when the exhaust gas flow rate is high, the back pressure upstream of the exhaust throttle valve 10 may increase, and the pump loss in the internal combustion engine 1 may increase.

  Therefore, in this embodiment, when the back pressure becomes a predetermined pressure or higher when the exhaust throttle valve 10 is closed during the filter regeneration control, the nozzle vane 17 of the turbocharger 8 is controlled in the valve opening direction. The supercharging pressure by the turbocharger 8 is reduced. Here, the predetermined pressure is a threshold value of the back pressure at which it can be determined that the pump loss in the internal combustion engine 1 increases excessively and the fuel consumption is worse than the allowable range.

  When the supercharging pressure by the turbocharger 8 is lowered, the intake air amount of the internal combustion engine 1 is reduced. For this reason, the flow rate of the exhaust gas inevitably decreases. As a result, an increase in back pressure when the exhaust throttle valve 10 is closed can be suppressed.

  Next, a routine for executing the filter regeneration control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

In this routine, first, in S101, the ECU 20 determines whether or not the PM collection amount Qpm in the filter 9 is equal to or greater than a predetermined collection amount Qpm0 that is a threshold value for executing the filter regeneration control. The PM collection amount Qpm in the filter 9 is estimated from the history of the operating state of the internal combustion engine 1 or the like. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the ECU 20 once ends the execution of this routine.

  In S102, the ECU 20 determines whether or not the exhaust gas flow rate Gex is greater than or equal to a predetermined flow rate Gex0. If an affirmative determination is made in S102, the ECU 20 proceeds to S103, and if a negative determination is made, the ECU 20 proceeds to S111.

  In S103, the ECU 20 estimates the back pressure Pex when the exhaust throttle valve 10 is closed based on the exhaust gas flow rate Gex. The relationship between the exhaust gas flow rate Gex and the back pressure Pex when the exhaust throttle valve 10 is closed is obtained in advance by experiments or the like and stored in the ECU 20 as a map.

  Next, the ECU 20 proceeds to S104, and determines whether or not the estimated back pressure Pex is equal to or higher than a predetermined pressure Pex0. If an affirmative determination is made in S104, the ECU 20 proceeds to S105, and if a negative determination is made, the ECU 20 proceeds to S113.

  In step S105, the ECU 20 calculates a target opening degree Vt1 of the nozzle vane 17 of the turbocharger 8. When the nozzle vane 17 of the turbocharger 8 is controlled in the valve opening direction, the supercharging pressure by the turbocharger 8 is reduced and the intake air amount is reduced. When the amount of intake air decreases, the exhaust gas flow rate Gex also decreases, so that an increase in the back pressure Pex when the exhaust throttle valve 10 is closed can be suppressed. Here, the target opening degree Vt1 means that when the nozzle vane 17 is opened to the target opening degree Vt1 and the supercharging pressure is lowered, the back pressure Pex does not reach the predetermined pressure Pex0 even if the exhaust throttle valve 10 is closed. It is a value that can be judged not to rise. If the nozzle vane 17 is opened excessively, the intake air amount is excessively reduced. Therefore, the target opening degree Vt1 is set in a range where the intake air amount does not decrease excessively.

  Next, the ECU 20 proceeds to S106 and estimates the torque fluctuation amount ΔTr of the internal combustion engine 1 when the nozzle vane 17 of the turbocharger 8 is opened to the target opening degree Vt1. When the nozzle vane 17 is opened to the target opening Vt1, there is a case where the torque of the internal combustion engine 1 decreases due to a decrease in the intake air amount, or the torque of the internal combustion engine 1 increases due to a decrease in pump loss. is there.

  Next, the ECU 20 proceeds to S107, and determines whether or not the estimated torque fluctuation amount ΔTr of the internal combustion engine 1 is equal to or less than a fluctuation amount upper limit value ΔTrlimit which is an upper limit value of the allowable range. If an affirmative determination is made in S107, the ECU 20 proceeds to S108, and if a negative determination is made, the ECU 20 proceeds to S112.

  The ECU 20 having proceeded to S112 adjusts the fuel injection amount from the fuel injection valve 3 so as to compensate for the torque fluctuation of the internal combustion engine 1 caused by opening the nozzle vane 17 to the target opening Vt1. That is, when the nozzle vane 17 is opened, the amount of fuel injected from the fuel injection valve 3 is increased when the torque of the internal combustion engine 1 is reduced, and when the nozzle vane 17 is opened, the fuel injection valve is increased. The fuel injection amount from 3 is decreased. Thereafter, the ECU 20 proceeds to S108.

  In step S108, the ECU 20 opens the nozzle vane 17 to the target opening degree Vt1, and decreases the supercharging pressure.

Next, the ECU 20 proceeds to S109, and determines whether or not the exhaust gas flow rate Gex after opening the nozzle vane 17 to the target opening degree Vt1 is equal to or higher than a predetermined flow rate Gex0. If an affirmative determination is made in S109, the ECU 20 proceeds to S110. On the other hand, when the exhaust gas flow rate Gex becomes smaller than the predetermined flow rate Gex0 by opening the nozzle vane 17 to the target opening degree Vt1, it is not necessary to close the exhaust throttle valve 10. Therefore, if a negative determination is made in S109, the ECU 20 proceeds to S111.

  In S110, the ECU 20 closes the exhaust throttle valve 10.

  Next, the ECU 20 proceeds to S111 and executes fuel addition from the fuel addition valve 11. That is, filter regeneration control is executed. Thereafter, the ECU 20 once terminates execution of this routine.

  On the other hand, the ECU 20 having proceeded to S113 determines whether or not the temperature of the exhaust detected by the temperature sensor 18, that is, the temperature Tex of the exhaust flowing into the filter 9 is equal to or lower than a predetermined temperature Tex0. Here, the predetermined temperature Tex0 can be determined to be a temperature at which it can be determined that the oxidation of fuel in the NOx catalyst is not easily promoted, that is, in order to promote the oxidation of fuel in the NOx catalyst, it is preferable to raise the temperature of the exhaust more. This is the temperature threshold. If an affirmative determination is made in S113, the ECU 20 proceeds to S114, and if a negative determination is made, the ECU 20 proceeds to S110.

  In step S114, the ECU 20 calculates the target opening degree Vt2 of the nozzle vane 17 of the turbocharger 8. If the supercharging pressure is lowered by controlling the nozzle vanes 17 of the turbocharger 8 in the valve opening direction, the energy of the exhaust gas used for supercharging by the turbocharger 8 can be reduced. As a result, the exhaust gas temperature drop in the turbocharger 8 can be suppressed. That is, the temperature Tex of the exhaust gas flowing into the filter 9 can be further increased.

  Here, the target opening degree Vt2 means that the temperature Tex of the exhaust gas flowing into the filter 9 is made higher than the predetermined temperature Tex0 by opening the nozzle vane 17 to the target opening degree Vt2 and reducing the supercharging pressure. It is a value that can be determined to be possible. Note that the target opening degree Vt2 is also set within a range in which the intake air amount does not decrease excessively, similarly to the above-described target opening degree Vt1.

  Next, the ECU 20 proceeds to S106. In this case, the ECU 20 estimates the torque fluctuation amount ΔTr of the internal combustion engine 1 when the nozzle vane 17 of the turbocharger 8 is opened to the target opening degree Vt2 in S106. Further, when the routine proceeds to S112, the ECU 20 adjusts the fuel injection amount from the fuel injection valve 3 so as to compensate for the torque fluctuation of the internal combustion engine 1 by opening the nozzle vane 17 to the target opening Vt2. After that, the ECU 20 that has proceeded to S108 opens the nozzle vane 17 to the target opening Vt2, and the ECU 20 that has proceeded to S109 has the exhaust gas flow rate Gex after the nozzle vane 17 has been opened to the target opening Vt2 as the predetermined flow rate. It is determined whether it is Gex0 or more.

  According to the routine described above, when it is predicted that the back pressure Pex will be equal to or higher than the predetermined pressure Pex0 when the exhaust throttle valve 10 is closed because the flow rate of the exhaust gas is large when the filter regeneration control is executed, the nozzle vane 17 Is controlled in the valve opening direction to reduce the supercharging pressure by the turbocharger 8. Thereby, when the exhaust throttle valve 10 is closed, it is possible to suppress the back pressure Pex from rising to a predetermined pressure Pex0 or more.

  Therefore, according to the present embodiment, it is possible to suppress an excessive increase in pump loss in the internal combustion engine 1 when the filter regeneration control is executed. As a result, it becomes possible to suppress deterioration in fuel consumption.

  Further, according to the above routine, even when the back pressure Pex when the exhaust throttle valve 10 is closed is lower than the predetermined pressure Pex0 when the filter regeneration control is executed, the temperature Tex of the exhaust gas flowing into the filter 9 is the same. When the temperature is equal to or lower than the predetermined temperature Tex0, the supercharging pressure by the turbocharger 8 is reduced. Thereby, since the temperature Tex of the exhaust gas rises, the oxidation of the fuel in the NOx catalyst can be further promoted, and hence the oxidation of PM can be further promoted.

  In the present embodiment, when the exhaust throttle valve 10 is closed because the flow rate of the exhaust gas is large when the filter regeneration control is executed, the exhaust throttle valve 10 does not necessarily need to be fully closed, and the opening degree is not limited. It is sufficient to set the opening so that the flow rate of the exhaust gas is suppressed to the extent that the amount of fuel that is not oxidized in the NOx catalyst is within the allowable range.

  Further, in the filter regeneration control according to the present embodiment, fuel is supplied to the NOx catalyst by performing sub fuel injection after the main fuel injection by the fuel injection valve 3 instead of fuel addition by the fuel addition valve 11. Also good.

  In the NOx reduction control for reducing NOx stored in the NOx catalyst supported by the filter 9 and the SOx poisoning recovery control for reducing SOx stored in the NOx catalyst, fuel is supplied to the NOx catalyst. Is called. Therefore, when the exhaust throttle valve 10 is closed during execution of these controls, the control of the supercharging pressure in the filter regeneration control described above may be applied. In this case, it is possible to suppress an increase in pump loss in the internal combustion engine 1 during the execution of the NOx reduction control and the SOx poisoning recovery control.

The figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake / exhaust system. The figure which shows schematic structure of the turbocharger which concerns on an Example. The flowchart which shows the routine for performing filter reproduction | regeneration control based on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake passage 5 ... Intake manifold 6 ... Exhaust passage 7 ... Exhaust manifold 8 ... Turbocharger 8a, Compressor 8b, Turbine 9 ... Particulate Filter 10 .. Exhaust throttle valve 11 .. Fuel addition valve 12 .. Air flow meter 13 .. Actuator 14 .. Compressor wheel 15 .. Turbine wheel 17 .. Nozzle vane 18 .. Temperature sensor 20.

Claims (2)

A turbocharger with variable supercharging pressure;
An exhaust purification device provided in the exhaust passage;
Reducing agent supply means for supplying a reducing agent to the exhaust gas purification device in order to restore the performance of the exhaust gas purification device;
An exhaust throttle valve provided in the exhaust passage for controlling the flow rate of the exhaust;
An exhaust throttle valve control for controlling the exhaust throttle valve in a valve closing direction when the flow rate of the exhaust gas flowing through the exhaust passage is greater than or equal to a predetermined flow rate when the reducing agent is supplied to the exhaust gas purification device by the reducing agent supply means. Means, and
When the reducing agent is supplied to the exhaust gas purification device by the reducing agent supply means, when the back pressure when the exhaust throttle valve control means controls the exhaust throttle valve in the valve closing direction is a predetermined pressure or more, An exhaust gas purification system for an internal combustion engine, wherein a supercharging pressure by the supercharger is reduced. The turbocharger is a turbocharger having a turbine provided upstream of the exhaust purification device in the exhaust passage;
When the reducing agent is supplied to the exhaust purification device by the reducing agent supply means, the back pressure when the exhaust throttle valve control means controls the exhaust throttle valve in the valve closing direction is lower than the predetermined pressure. However, when the temperature of the exhaust gas flowing into the exhaust gas purification apparatus is equal to or lower than a predetermined temperature, the supercharging pressure by the turbocharger is reduced.

Images