JP2008169753A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

In an exhaust gas purification system for an internal combustion engine having a variable capacity turbocharger, when there is a demand to raise exhaust gas flowing into the exhaust gas purification catalyst, it is possible to suitably raise the temperature of the exhaust gas flowing into the exhaust gas purification catalyst. Technology.
When a variable nozzle VN opening degree θvn is decreased, a first temperature increase amount ΔTu1 resulting from an increase in back pressure Pe and a second temperature increase amount resulting from increasing a fuel injection amount QF. The second target VN opening tθvn2 of the variable nozzle is obtained so that a value obtained by subtracting the first temperature decrease amount ΔTd1 resulting from the increase in the turbine speed Nt from the sum of ΔTu2 is substantially equal to the target temperature increase amount ΔTut. (S109). Then, the VN opening θvn is decreased to the second target VN opening tθvn2, and the fuel injection amount QF is increased by the increased injection amount ΔQF (S110).
[Selection] Figure 4

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine having a variable capacity turbocharger.

  In exhaust purification systems equipped with exhaust purification catalysts that purify exhaust, such as NOx storage reduction catalysts, oxidation catalysts, and three-way catalysts, when the internal combustion engine is idling or when the engine torque is excessively low, A temperature increase request may be issued. This is because the fuel injection amount supplied to the internal combustion engine is excessively reduced, so that the temperature of the exhaust gas discharged from the internal combustion engine is lowered, and as a result, the temperature of the catalyst is lowered.

In contrast, in an exhaust gas purification system for an internal combustion engine having a variable capacity turbocharger, the opening of the variable nozzle of the variable capacity turbocharger is increased to reduce the heat loss in the turbine, thereby reducing the exhaust flowing into the exhaust gas purification catalyst. A technique for raising the temperature has been proposed (see, for example, Patent Document 1).
JP 2002-285824 A JP 2003-120368 A JP 2005-42664 A

  However, depending on the operating state of the internal combustion engine, there are cases where the rotational speed of the turbine does not change even when the opening of the variable nozzle is changed to the open side as in the prior art. In such a case, since the heat energy consumed for rotating the turbine does not decrease, the exhaust gas flowing into the exhaust purification catalyst may not be heated appropriately. As a result, the temperature of the exhaust purification catalyst may be excessively lowered, and the exhaust purification capability of the exhaust purification catalyst may be significantly reduced.

  The present invention has been made in view of the above prior art, and an object thereof is to suitably raise the temperature of exhaust gas flowing into an exhaust purification catalyst in an exhaust purification system of an internal combustion engine having a variable capacity turbocharger. Is to provide possible technology.

In order to achieve the above object, the control device for an internal combustion engine with a variable capacity turbocharger according to the present invention employs the following means. That is,
An exhaust purification system for an internal combustion engine having a variable capacity turbocharger provided with a variable nozzle,
An exhaust purification catalyst provided in an exhaust passage downstream of the turbine of the variable capacity turbocharger;
Nozzle opening control means for controlling the opening of the variable nozzle;
With
The nozzle opening degree control means reduces the opening degree of the variable nozzle to a target opening degree when raising the inflow exhaust gas temperature, which is the temperature of the exhaust gas flowing into the exhaust purification catalyst,
The target opening degree is such that a first temperature increase amount, which is an increase amount of the inflow exhaust gas temperature due to an increase in back pressure upstream of the turbine in the exhaust passage, increases the rotational speed of the turbine. It is determined to be larger than a first temperature decrease amount that is a decrease amount of the inflow exhaust gas temperature due to the above.

  Therefore, in the present invention, when the inflow exhaust gas temperature is raised, the nozzle opening degree control means reduces the opening degree of the variable nozzle to the target opening degree. As a result, the back pressure upstream of the turbine in the exhaust passage becomes higher, and the temperature of the exhaust flowing into the turbine rises.

  By the way, when the rotational speed of the turbine is increased by reducing the opening of the variable nozzle to the target opening, the supercharging pressure rises and the intake air amount sucked into the internal combustion engine increases. If it does so, the calorie | heat amount per unit volume of the exhaust_gas | exhaustion discharged | emitted from an internal combustion engine will reduce. Furthermore, when the rotational speed of the turbine increases, the heat energy of the exhaust consumed in the turbine increases. As a result, the heat loss of the exhaust gas passing through the turbine increases as the rotational speed of the turbine increases. Therefore, when the rotational speed of the turbine is excessively increased when the opening of the variable nozzle is decreased to the target opening, the inflow exhaust gas temperature may be lowered.

  On the other hand, in the present invention, the target opening degree is determined so that the first temperature increase amount is larger than the first temperature decrease amount. Thus, the temperature of the exhaust gas flowing into the exhaust purification catalyst can be raised by a value obtained by subtracting the first temperature decrease amount from the first temperature increase amount.

  In the present invention, the inflow exhaust gas temperature can be increased as the first temperature decrease amount is smaller. Therefore, the target opening degree may be determined within a range in which the increase amount of the rotational speed of the turbine is substantially zero.

  In this case, the amount of intake air taken into the internal combustion engine does not increase. Therefore, it can suppress that the calorie | heat amount per unit volume of the exhaust_gas | exhaustion discharged | emitted from an internal combustion engine reduces. Moreover, it can suppress that the heat loss when exhaust_gas | exhaustion passes a turbine increases. That is, it is possible to reduce the first temperature decrease amount resulting from the increase in the rotational speed of the turbine to substantially zero. Therefore, the inflow exhaust gas temperature can be raised more suitably.

  Further, the target opening in the present invention may be a minimum opening (opening on the most closed side) at which the amount of increase in the rotational speed of the turbine can be made substantially zero. The larger the degree of decrease in the opening of the variable nozzle, the higher the back pressure on the upstream side of the turbine can be increased, and thus the first temperature increase amount can be increased. is there.

  In the present invention, the amount of decrease in the torque of the internal combustion engine due to the decrease in the opening of the variable nozzle is acquired, and the amount of decrease in the torque before and after the opening of the variable nozzle decreases is predetermined. There may be further provided a fuel injection amount increasing means for increasing the fuel injection amount of the internal combustion engine so as to be equal to or less than the allowable value.

  When the back pressure on the upstream side of the turbine increases due to the decrease in the opening of the variable nozzle, the pump loss of the internal combustion engine increases and the torque decreases. The amount of torque reduction described above means the amount of reduction in engine torque that decreases by reducing the opening of the variable nozzle to the target opening. Further, the “predetermined allowable value” means an allowable value of a torque reduction amount that is allowed according to the driving state. For example, the torque reduction amount is such that the driver does not feel a so-called torque shock. good.

  Further, the predetermined allowable value may be substantially zero. That is, the fuel injection amount increasing means in the present invention may increase the fuel injection amount so that the torque change amount becomes substantially zero. Thereby, what is called a torque shock can be suppressed reliably.

In the present invention, the amount of heat per unit volume of the exhaust discharged from the internal combustion engine increases as the amount of increase in the fuel injection amount increases. Here, if the amount of increase in the inflow exhaust temperature resulting from the increase in the fuel injection amount is the second temperature increase amount, the more the first temperature increase amount and the second temperature increase amount, or the first temperature decrease. The smaller the amount, the higher the inflow exhaust gas temperature can be raised.

  Hereinafter, the relationship between the target opening degree and the first temperature increase amount, the second temperature increase amount, and the first temperature decrease amount will be described. For example, the smaller the target opening, the higher the back pressure on the upstream side of the turbine in the exhaust passage, so the first temperature rise amount becomes larger. And as the back pressure increases, the pump loss of the internal combustion engine increases, so the amount of torque decrease increases. As a result, the amount of increase in the fuel injection amount required to make the torque decrease amount equal to or less than the predetermined allowable value increases. Accordingly, the second temperature increase amount increases as the target opening degree decreases.

  Further, since the amount of increase in the turbine speed increases as the target opening degree decreases, the intake air amount of the internal combustion engine increases, and the heat loss of the exhaust gas in the turbine increases. That is, the first temperature decrease amount increases as the target opening degree decreases. On the other hand, it is considered that the larger the target opening, the smaller the first temperature rise amount, the second temperature rise amount, and the first temperature drop amount, contrary to the above.

  As described above, the present invention opens the target so that the inflow exhaust gas temperature rises based on the magnitudes of the first temperature rise amount, the second temperature rise amount, and the first temperature drop amount when the opening of the variable nozzle is decreased. It is preferable to determine the degree.

  Therefore, the target opening in the present invention is the sum of the second temperature increase amount and the first temperature increase amount, which is the increase amount of the inflow exhaust gas temperature due to the increase of the fuel injection amount. You may determine so that it may become larger than 1 amount of temperature fall. Thereby, inflow exhaust gas temperature can be raised reliably.

  Further, the target opening in the present invention is such that a value obtained by subtracting the first temperature decrease amount from the sum of the first temperature increase amount and the second temperature increase amount increases the inflow exhaust gas temperature to the target temperature. It may be determined so as to be substantially equal to the amount of temperature increase required for the above. Thereby, the inflow exhaust gas temperature can be reliably raised to the target temperature. That is, the temperature of the exhaust purification catalyst can be suitably raised.

  In the present invention, in the exhaust gas purification system for an internal combustion engine having a variable capacity turbocharger, the temperature of the exhaust gas flowing into the exhaust gas purification catalyst can be suitably raised. And the temperature of an exhaust purification catalyst can be raised suitably, and it can suppress that the exhaust purification capability in an exhaust purification catalyst falls remarkably.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its intake / exhaust system and control system in this embodiment. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders 2. The internal combustion engine 1 is provided with a fuel injection valve 3 for injecting fuel directly into the combustion chamber of the cylinder 2 in each cylinder.

<Intake system>
An intake manifold 8 is connected to the internal combustion engine 1, and each branch pipe of the intake manifold 8 is communicated with a combustion chamber of each cylinder 2 through an intake port. An intake throttle valve 11 capable of adjusting the flow rate of the intake air flowing through the intake passage 9 is provided in the vicinity of the connection portion between the intake manifold 8 and the intake passage 9. An intercooler 4 for cooling the gas flowing through the intake passage 9 is provided upstream of the intake throttle valve 11 in the intake passage 9.

  Further, a compressor housing 25 a of a variable displacement turbocharger (hereinafter also simply referred to as “turbocharger”) 25 that operates using exhaust energy as a drive source is provided upstream of the intercooler 4 in the intake passage 9. ing. An air flow meter 5 that outputs an electrical signal corresponding to the amount of intake air flowing through the intake passage 9 is disposed upstream of the compressor housing 25a, and an air cleaner 6 is disposed upstream of the air flow meter 5. Is provided.

  In the intake system of the internal combustion engine 1 configured as described above, dust and dirt in the intake air are removed by the air cleaner 6 and then flow into the compressor housing 25 a via the intake passage 9. The intake air flowing into the compressor housing 25a is compressed by the rotation of the compressor wheel 27 built in the compressor housing 25a. The compressed intake air having a high temperature is cooled by the intercooler 4, and then the flow rate is adjusted by the intake throttle valve 11 as necessary to flow into the intake manifold 8. The intake air that has flowed into the intake manifold 8 is distributed to each cylinder 2 via each branch pipe, and is burned by using the fuel injected from the fuel injection valve 3 of each cylinder 2 as an ignition source.

<Exhaust system>
On the other hand, an exhaust manifold 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust manifold 18 is connected to a combustion chamber of each cylinder 2 via an exhaust port. A turbine housing 25 b of a turbocharger 25 is connected to the exhaust manifold 18. An exhaust passage 19 is connected to the turbine housing 25 b, and an occlusion reduction type NOx catalyst (hereinafter simply referred to as “NOx catalyst”) 20 is provided in the middle of the exhaust passage 19. Further, a first temperature sensor 15 and a second temperature sensor 16 for detecting the temperature of the exhaust are provided on the upstream side and the downstream side of the NOx catalyst 20 in the exhaust passage 19. The exhaust passage 19 is connected to a muffler (not shown) downstream. Here, in this embodiment, the NOx catalyst 20 corresponds to the exhaust purification catalyst in the present invention.

  In the exhaust system of the internal combustion engine 1 configured as described above, the burned gas burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 through the exhaust port, and then from the exhaust manifold 18 to the turbocharger 25. It flows into the turbine housing 25b. The exhaust gas that has flowed into the turbine housing 25b rotates the turbine wheel 28 that is rotatably supported in the turbine housing 25b using the thermal energy of the exhaust gas. At that time, the rotational torque of the turbine wheel 28 is transmitted to the compressor wheel 27 of the compressor housing 25a.

  The exhaust gas flowing out from the turbine housing 25b flows into the NOx catalyst 20 through the exhaust passage 19, and after NOx in the exhaust gas is occluded, it is released into the atmosphere through the muffler.

<Variable capacity turbocharger>
Next, the variable capacity turbocharger 25 in the present embodiment will be described. FIG. 2 is a cross-sectional view showing a schematic configuration of the turbocharger 25 in the present embodiment. The turbocharger 25 includes a compressor housing 25a disposed in the middle of the intake passage 9, a turbine housing 25b disposed in the exhaust passage 19, and a center housing 25c provided between the compressor housing 25a and the turbine housing 25b. I have. A rotor shaft 26 is supported on the center housing 25c so as to be rotatable about its axis, and one end of the rotor shaft 26 is attached to a compressor wheel 27 disposed in the compressor housing 25a. The other end of the rotor shaft 26 is attached to a turbine wheel 28 disposed in the turbine housing 25b.

  In the turbocharger 25 configured as described above, the turbine wheel 28 rotates when the exhaust is blown, and the compressor wheel 27 also rotates when the turbine wheel 28 rotates. Then, due to the rotation of the compressor wheel 27, the intake air sent to the intake passage 9 downstream of the compressor wheel 27 is supercharged.

  Further, in the turbine housing 25b, a plurality of blade-shaped nozzle vanes 29 are attached in the circumferential direction of the turbine wheel 28 as shown in FIG. FIG. 3 is a side sectional view of the turbine housing showing a schematic arrangement of the nozzle vanes 29 in the present embodiment. The turbine housing 25b is provided with a nozzle vane actuator 30 that drives the nozzle vane 29 to open and close. When the nozzle vane 29 is opened and closed by the nozzle vane actuator 30, the size of the gap between the adjacent nozzle vanes 29 changes, and the flow velocity of the exhaust gas blown to the turbine wheel 28 changes. At that time, the supercharging pressure to the intake passage 9 on the downstream side of the compressor wheel 27 can be adjusted by changing the rotational speed and torque of the turbine wheel 28 and the compressor wheel 27. In this embodiment, the gap between the adjacent nozzle vanes 29 constitutes the variable nozzle in the present invention.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1 and the intake / exhaust system. The ECU 10 controls the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition, the ECU 10 includes sensors such as an air flow meter 5, a crank position sensor 13 that detects the engine speed, an accelerator position sensor 14 that detects the accelerator opening, a first temperature sensor 15, and a second temperature sensor 16. They are connected via wiring, and their output signals are input to the ECU 10. On the other hand, the fuel injection valve 3, the intake throttle valve 11, the nozzle vane actuator 30 and the like are connected to the ECU 10 via electric wiring, and are controlled by the ECU 10.

  The ECU 10 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. Further, a temperature raising control routine for raising the temperature of exhaust gas flowing into the NOx catalyst 20 described later is one of programs stored in the ROM of the ECU 10.

<Inflow exhaust temperature rise control>
Next, inflow exhaust gas temperature increase control for increasing the temperature of exhaust gas flowing into the NOx catalyst 20 in the present embodiment (hereinafter simply referred to as “inflow exhaust gas temperature”) Tin will be described. When the operating state of the internal combustion engine 1 is in an idling state or when the engine torque Tq is extremely low, the fuel addition amount QF injected from the fuel injection valve 3 becomes excessively small. In such a case, the temperature of the NOx catalyst 20 (hereinafter, simply referred to as “catalyst temperature”) Tn is increased with respect to the NOx catalyst 20 in order to prevent the NOx purification efficiency from deteriorating due to excessively low Tn. A request is made.

  In this embodiment, when a temperature increase request for the NOx catalyst 20 is issued, the opening degree (hereinafter referred to as “VN opening degree”) θvn of the nozzle vane 29 is decreased. When the VN opening θvn decreases, the back pressure Pe upstream of the turbine housing 25b in the exhaust passage 19 increases, and the exhaust temperature rises upstream of the turbine housing 25b.

  Here, since the back pressure Pe increases as the VN opening degree θvn is further decreased to the closing side opening degree, the amount of increase in the inflow exhaust gas temperature Tin caused by the increase in the back pressure Pe (hereinafter referred to as “first” It is referred to as “temperature rise amount.”) ΔTu1 increases.

  However, if the VN opening θvn is too small, the rotational speed of the turbine wheel 28 (hereinafter referred to as “turbine rotational speed”) Nt increases. When the turbine speed Nt increases, the intake air amount Ga sucked into the internal combustion engine 1 increases. As a result, the amount of heat per unit volume of the exhaust discharged from the internal combustion engine 1 is considered to decrease. Further, since exhaust energy is consumed to increase the turbine rotational speed Nt, it is considered that the heat loss of the exhaust when the exhaust flows through the turbine housing 25b increases. Therefore, in the case where the turbine rotational speed Nt increases when the VN opening θvn is decreased, the inflow caused by the turbine rotational speed Nt increasing as the VN opening θvn is further decreased to the closing position. A decrease amount of the exhaust temperature Tin (hereinafter referred to as “first temperature decrease amount”) ΔTd1 increases.

  Therefore, in the present embodiment, the target opening (hereinafter, referred to as “target VN opening”) tθvn of the nozzle vane 29 is determined so that the first temperature increase amount ΔTu1 is larger than the first temperature decrease amount ΔTd1. Then, the VN opening degree θvn is decreased to the target VN opening degree tθvn. Thereby, inflow exhaust gas temperature Tin can be raised suitably. And it is suppressed that the catalyst temperature Tn becomes too low and the purification efficiency of NOx deteriorates.

  In order to raise the inflow exhaust gas temperature Tin to a higher temperature, it is preferable that the first temperature decrease amount ΔTd1 is as small as possible and the first temperature increase amount ΔTu1 is as large as possible. Accordingly, the target VN opening tθvn in the inflow exhaust gas temperature rise control of the present embodiment is the smallest opening within a range where the increase amount ΔNt of the turbine rotation speed when the VN opening θvn is decreased becomes substantially zero. 1 target VN opening tθvn1 may be sufficient. As a result, the first temperature increase amount ΔTu1 becomes substantially zero, and the inflow exhaust gas temperature Tin can be suitably increased.

  However, when the original inflow exhaust gas temperature Tin is excessively low, or when the target temperature tTin required for the inflow exhaust gas temperature Tin is high, the back pressure Pe is set within a range in which the increase amount ΔNt of the turbine speed is substantially zero. It may be difficult to raise the inflow exhaust gas temperature Tin to the target temperature tTin required for the inflow exhaust gas temperature Tin simply by raising it.

  In such a case, in this embodiment, the target VN opening tθvn is set to the second target VN opening tθvn2 that is the opening closer to the closing side than the first target VN opening tθvn1. In this case, the first temperature decrease amount ΔTd1 is increased in order to allow the turbine rotational speed Nt to increase. However, rather than reducing the VN opening θvn to the first target VN opening tθvn1, it is more difficult to reduce the VN opening θvn to the second target VN opening tθvn2, which is the opening closer to the first target VN opening tθvn1. Since the pressure Pe increases, the first temperature increase amount ΔTu1 can be increased.

  Further, when the back pressure Pe increases, the pump loss in the internal combustion engine 1 increases. Therefore, if the fuel injection amount QF is constant, the engine torque Tq of the internal combustion engine 1 decreases. In this embodiment, the fuel injection amount QF is corrected to increase to compensate for the decrease in the engine torque Tq. Specifically, the engine torque decrease amount (hereinafter simply referred to as “torque decrease amount”) ΔTq before and after the VN opening θvn is decreased to the second target VN opening tθvn2 is an allowable torque decrease amount according to the operating state. The fuel injection amount QF is increased by the increased injection amount ΔQF so as to be equal to or less than ΔTql. For example, the allowable torque decrease amount ΔTql may be a value that allows for a certain margin in the torque decrease amount ΔTq with which the driver can sense a torque shock. In this embodiment, the allowable torque reduction amount ΔTql corresponds to a predetermined allowable value in the present invention.

  Here, the pump loss of the internal combustion engine 1 increases as the second target VN opening tθvn2 is more closed. Therefore, the increased injection amount ΔQF can be increased, and the amount of heat per unit volume of the exhaust discharged from the internal combustion engine 1 can be increased. That is, the increase amount of the inflow exhaust gas temperature Tin caused by increasing the fuel injection amount QF (hereinafter referred to as “second temperature increase amount”) ΔTu2 can be increased.

  The first temperature increase amount ΔTu1 and the second temperature increase amount ΔTu2 that increase the inflow exhaust gas temperature Tin and the first temperature decrease amount ΔTd1 that decreases the inflow exhaust gas temperature Tin are the operating state of the internal combustion engine 1, the current VN opening degree rθvn. The second target VN opening tθvn2 is changed. In this embodiment, the value obtained by subtracting the first temperature decrease amount ΔTd1 from the sum of the first temperature increase amount ΔTu1 and the second temperature increase amount ΔTu2 in accordance with the operating state of the internal combustion engine 1, etc., makes the inflow exhaust gas temperature Tin the target temperature. The second target VN opening tθvn2 is determined so as to be substantially equal to the target temperature increase amount ΔTut necessary for increasing to tTin.

  As a result, the inflow exhaust gas temperature Tin can be reliably raised to the target temperature tTin. In the present embodiment, the first temperature increase amount ΔTu1, the second temperature increase amount ΔTu2, and the first temperature decrease amount ΔTd1 correspond to the first temperature increase amount, the second temperature increase amount, and the first temperature decrease amount in the present invention.

  Hereinafter, the inflow exhaust gas temperature rise control performed by the ECU 10 will be described with reference to the flowchart of FIG. FIG. 4 is a flowchart showing an inflow exhaust gas temperature rise control routine in the present embodiment. This routine is a program stored in the ROM in the ECU 10, and is executed every predetermined period. In the present embodiment, the first target VN opening tθvn1 and the second target VN opening tθvn2 correspond to the target opening of the variable nozzle in the present invention. Further, the ECU 10 that issues a command to the nozzle vane actuator 30 to reduce the VN opening θvn to the first target VN opening tθvn1 or the second target VN opening tθvn2 corresponds to the nozzle opening control means in the present invention.

  First, in step S101, the inflow exhaust gas temperature Tin is estimated based on the detection value of the first temperature sensor 15. Further, the catalyst temperature Tn is estimated based on the detection value of the second temperature sensor 16. In subsequent step S102, it is determined whether or not the catalyst temperature Tn is lower than the activation temperature Tna (for example, 200 ° C. to 250 ° C.). When it is determined that the catalyst temperature Tn is lower than the activation temperature Tna, it is determined that the inflow exhaust gas temperature Tin needs to be increased, and the process proceeds to step S103. On the other hand, when it is determined that the catalyst temperature Tn is equal to or higher than the activation temperature Tna, this routine is temporarily terminated.

  In step S103, the ECU 10 detects the operating state of the internal combustion engine 1. Specifically, the engine speed NE of the internal combustion engine 1 is acquired from the detection value of the crank position sensor 13, and the engine torque Tq is acquired from the detection value of the accelerator position sensor 14. Then, when step S103 is completed, the process proceeds to step S104.

  In step S104, the ECU 10 calculates the first target VN opening tθvn1 corresponding to the operating state. That is, the minimum opening in the range where the increase amount ΔNt of the turbine rotation speed is substantially zero is obtained. The first target VN opening tθvn1 is experimentally obtained in advance according to the operating state (engine torque Tq, engine speed NE) of the internal combustion engine 1, and is stored in the ROM of the ECU 10 as a function or map of the operating state of the internal combustion engine 1. It is remembered. Then, when the process of step S104 ends, the process proceeds to step S105.

In step S105, a back pressure increase amount ΔPe, which is an increase amount of the back pressure Pe when the VN opening degree θvn is decreased from rθvn to the target VN opening degree tθvn, is estimated. The back pressure increase amount ΔPe is estimated based on the operating state of the internal combustion engine 1, the current VN opening degree rθvn, and the first target VN opening degree tθvn1. Then, when the process of step S105 ends, the process proceeds to step S106.

  In step S106, the first temperature increase amount ΔTu1 is estimated based on the back pressure increase amount ΔPe estimated in step S105. In subsequent step S107, it is determined whether or not the first temperature increase amount ΔTu1 is equal to or greater than the target temperature increase amount ΔTut. The inflow exhaust gas temperature Tin is the amount of temperature increase necessary to raise the inflow exhaust gas temperature Tin to the target temperature tTin as described above. The target temperature tTin in this routine is a temperature required for the exhaust gas flowing into the NOx catalyst 20 in order to raise the catalyst temperature Tn to the activation temperature Tna. The target temperature tTin may be the same temperature as the activation temperature Tna, or may be a temperature sufficiently higher than the activation temperature Tna.

  If it is determined that the first temperature increase amount ΔTu1 is equal to or greater than the target temperature increase amount ΔTut, the process proceeds to step S108. In step S108, the ECU 10 issues a command to the nozzle vane actuator 30, and the VN opening degree θvn is changed from the current VN opening degree rθvn to the first target VN opening degree tθvn1. As a result, the inflow exhaust gas temperature Tin can be raised to the target temperature tTin or higher by increasing the back pressure Pe. Then, when the process of step S108 ends, this routine is temporarily ended.

  If it is determined in step 107 that the first temperature increase amount ΔTu1 is lower than the target temperature increase amount ΔTut, the process proceeds to step 109. In step S109, the ECU 10 causes the second target VN opening so that a value obtained by subtracting the first temperature decrease amount ΔTd1 from the sum of the first temperature increase amount ΔTu1 and the second temperature increase amount ΔTu2 is equal to the target temperature increase amount ΔTut. The increased injection amount ΔQF corresponding to the degree tθvn2 and the second target VN opening tθvn2 is calculated based on the operating state of the internal combustion engine 1 and the current VN opening rθvn.

  In step S110, a command is issued from the ECU 10 to the fuel injection valve 3, and the fuel injection amount QF is increased by the increase injection amount ΔQF. Then, a command is issued from the ECU 10 to the nozzle vane actuator 30, and the VN opening degree θvn is reduced from the current VN opening degree rθvn to the second target VN opening degree tθvn2. In this embodiment, the ECU 10 that gives a command to the fuel injection valve 3 to increase the fuel injection amount QF corresponds to the fuel injection amount increase means in the present invention. When the process of step S110 is completed, this routine is temporarily ended.

  As described above, according to this routine, the target VN opening tθvn is obtained based on the relationship among the first temperature increase amount ΔTu1, the second temperature increase amount ΔTu2, and the first temperature decrease amount ΔTd1, and the inflow exhaust gas temperature Tin is determined. It is possible to reliably increase the temperature to the target temperature tTin. As a result, the catalyst temperature Tn can be quickly raised to the activation temperature Tna. That is, it is possible to suppress deterioration of the NOx purification efficiency in the NOx catalyst.

  In step S104 in this routine, the first target VN opening tθvn1 is determined as the minimum opening at which the amount of increase in the turbine rotational speed Nt can be made substantially zero, but the first target VN opening tθvn1 is It is not limited to. For example, the back pressure increase amount ΔPe when the first temperature increase amount ΔTu1 is substantially equal to the target temperature increase amount ΔTut may be obtained. Then, the first target VN opening tθvn1 may be derived from a map in which the relationship between the first target VN opening tθvn1 and the back pressure increase amount ΔPe is stored. The first target VN opening tθvn1 can be obtained as an opening that can make the inflow exhaust gas temperature Tin exactly the target temperature tTin.

  In this routine, the case where the inflow exhaust gas temperature Tin is raised when the catalyst temperature Tn is lower than the activation temperature Tna has been described as an example, but the present invention is not limited to this. For example, when it is determined that the inflow exhaust gas temperature Tin is lower than the target temperature tTin required for the operation state, it is preferable to apply the inflow exhaust gas temperature increase control in this embodiment.

  In the present embodiment, the fuel injection amount QF is increased so that the torque decrease amount ΔTq is equal to or less than the allowable torque decrease amount ΔTql. However, the present invention is not limited to this. For example, when the operating state of the internal combustion engine 1 is an idling state, it is considered that a certain amount of torque shock is allowed. In such a case, the fuel injection amount QF may be increased so that the engine torque Tq after changing the VN opening θvn becomes larger than the engine torque Tq before decreasing the VN opening θvn. The inflow exhaust gas temperature Tin can be raised to a higher temperature.

  In this embodiment, when a request to increase the inflow exhaust gas temperature Tin is issued, first, the VN opening degree θvn is decreased from the current VN opening degree rθvn to the closing side VN opening degree. As a result, the engine torque Tq When the fuel pressure decreases, the fuel injection amount QF may be increased so as to cancel out the torque decrease amount ΔTq. Then, the inflow exhaust gas temperature Tin is estimated from the detection value of the first temperature sensor 15, and when the inflow exhaust gas temperature Tin has not risen to the target temperature tTin, the above control is performed until the inflow exhaust gas temperature Tin rises to the target temperature tTin. May be implemented in a feedback manner.

  Further, in the present embodiment, the case where the present invention is applied to the exhaust purification system including the NOx storage reduction catalyst has been described as an example. However, different types of catalysts (for example, oxidation catalysts) are used instead of the NOx storage reduction catalyst. The present invention can also be applied to an exhaust purification system including a catalyst and a selective reduction type NOx catalyst. Further, the internal combustion engine 1 may be a gasoline engine. In this case, the present invention can be applied to an exhaust purification system including, for example, a three-way catalyst.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system and a control system thereof in Embodiment 1. FIG. It is sectional drawing which shows schematic structure of the turbocharger in Example 1. FIG. 1 is a side cross-sectional view of a turbine housing illustrating a schematic arrangement of nozzle vanes in Embodiment 1. FIG. 3 is a flowchart illustrating an inflow exhaust gas temperature rise control routine in the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Intercooler 5 ... Air flow meter 6 ... Air cleaner 8 ... Intake manifold 9 ... Intake passage 10 ... ECU
11. ・ Intake throttle valve 13 ・ ・ Crank position sensor 14 ・ Accelerator position sensor 15 ・ ・ First temperature sensor 16 ・ ・ Second temperature sensor 18 ・ ・ Exhaust manifold 19 ・ ・ Exhaust passage 20 ・ ・ Occlusion reduction type NOx catalyst ··· Variable displacement turbocharger 25a · Compressor housing 25b · Turbine housing 25c · Center housing 26 · · Rotor shaft 27 · Compressor wheel 28 · · Turbine wheel 29 · · Nozzle vane 30 · · Nozzle vane actuator

Claims (4)

An exhaust purification system for an internal combustion engine having a variable capacity turbocharger provided with a variable nozzle,
An exhaust purification catalyst provided in an exhaust passage downstream of the turbine of the variable capacity turbocharger;
Nozzle opening control means for controlling the opening of the variable nozzle;
With
The nozzle opening degree control means reduces the opening degree of the variable nozzle to a target opening degree when raising the inflow exhaust gas temperature, which is the temperature of the exhaust gas flowing into the exhaust purification catalyst,
The target opening degree is such that a first temperature increase amount, which is an increase amount of the inflow exhaust gas temperature due to an increase in back pressure upstream of the turbine in the exhaust passage, increases the rotational speed of the turbine. An exhaust gas purification system for an internal combustion engine, wherein the exhaust gas purification system is determined to be larger than a first temperature decrease amount that is a decrease amount of the inflow exhaust gas temperature due to the above.   The exhaust purification system for an internal combustion engine according to claim 1, wherein the target opening is determined within a range in which the amount of increase in the rotational speed of the turbine is substantially zero. The amount of decrease in the torque of the internal combustion engine due to the decrease in the opening degree of the variable nozzle is acquired, and the amount of decrease in the torque before and after the opening degree of the variable nozzle decreases is less than a predetermined allowable value. Further comprising a fuel injection amount increasing means for increasing the fuel injection amount of the internal combustion engine,
The target opening is such that the sum of the second temperature increase amount and the first temperature increase amount, which is the increase amount of the inflow exhaust gas temperature due to the increase of the fuel injection amount, is greater than the first temperature decrease amount. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas purification system is determined so as to be larger.   The target opening is a temperature increase required for the value obtained by subtracting the first temperature decrease amount from the sum of the first temperature increase amount and the second temperature increase amount to increase the inflow exhaust gas temperature to the target temperature. 4. The exhaust gas purification system for an internal combustion engine according to claim 3, wherein the exhaust gas purification system is determined to be substantially equal to the amount.

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