JP4775282B2 - Exhaust control device for internal combustion engine - Google Patents

Description

  The present invention relates to exhaust control of an internal combustion engine including an exhaust gas recirculation passage that recirculates exhaust gas from an exhaust passage to an intake passage.

  2. Description of the Related Art Conventionally, there is known an exhaust purification system for an internal combustion engine that is provided with a fuel addition valve for adding fuel to an exhaust passage and adds fuel for regeneration of an exhaust purification device such as a catalyst or a filter. For example, when a nitrogen oxide (NOx) occlusion reduction type catalyst is provided as an exhaust purification device, NOx is reduced by adding fuel as a reducing agent from a fuel addition valve to make exhaust rich. Japanese Patent Application Laid-Open No. H10-228667 describes a method of executing a plurality of times of fuel addition in synchronization with a crank angle of an internal combustion engine when fuel is added to exhaust gas for NOx reduction.

  On the other hand, an exhaust gas recirculation (EGR) device is known in which a part of exhaust gas discharged from an internal combustion engine to the exhaust passage is recirculated to the intake side to lower the combustion temperature and suppress the generation of NOx. In Patent Document 2, in addition to an EGR device that recirculates exhaust gas from a position upstream of the catalyst in the exhaust passage to the intake side, an exhaust gas that includes an EGR device that recirculates exhaust gas from a position downstream of the catalyst to the intake side. A purification system is described.

JP 2002-106332 A JP-A-2005-76456

In the case of an exhaust gas purification system including an EGR device that recirculates exhaust gas to the intake side from the downstream side of the fuel addition valve as in Patent Document 2, carbon dioxide (CO ₂ ) generated in the catalyst and DPF by the fuel addition is on the intake side. For example, the combustion state of the internal combustion engine may fluctuate and the torque may fluctuate. In order to prevent this torque fluctuation, it is effective to add fuel at regular intervals in synchronization with the crank angle. However, since the fuel addition valve has a property that the accuracy of the injection amount decreases if the injection amount is too small, if the number of fuel additions increases and one fuel addition amount becomes smaller than the minimum injection amount of the fuel addition valve, There is a problem that the accuracy of the injection amount is lowered and the controllability is deteriorated.

  The present invention has been made in view of the above points, and in an exhaust gas purification apparatus including an exhaust gas recirculation device that recirculates exhaust gas downstream from a fuel addition valve provided in an exhaust passage, while ensuring the accuracy of fuel addition. It aims at suppressing the fluctuation | variation of the combustion by fuel addition.

In one aspect of the present invention, an exhaust control device for an internal combustion engine includes an exhaust purification device provided in an exhaust passage of the internal combustion engine, and fuel addition means provided in an upstream position of the exhaust purification device in the exhaust passage. A first exhaust gas recirculation device that recirculates exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to an intake air side of the internal combustion engine, and an internal combustion engine from a downstream position of the exhaust gas purification device in the exhaust passage. A second exhaust gas recirculation device for recirculating exhaust gas to the intake side, a temperature sensor for detecting the temperature of the exhaust gas purification device, and an addition control means for adding fuel into the exhaust gas using the fuel addition means. wherein the addition control means determines a single unit amount is an amount of fuel added by the fuel addition, each control interval that is set in the reaction time of the temperature sensor, the single When the addition amount is smaller than the minimum injection amount of the fuel addition means, the fuel addition is performed at the minimum injection amount, and the surplus fuel amount when the fuel addition is performed at the minimum injection amount Reduce from the amount added in the addition.

  In the exhaust control device for an internal combustion engine described above, an exhaust purification device such as a DPF and a NOx storage reduction catalyst is provided on the exhaust passage. Fuel addition means such as a fuel addition valve is provided upstream of the exhaust purification device. The fuel addition means can add fuel to the exhaust passage for catalyst regeneration such as PM regeneration for the DPF, NOx reduction for the NOx storage reduction catalyst, and sulfur poisoning recovery. In addition, a first exhaust gas recirculation device that recirculates exhaust gas from the upstream side of the exhaust gas purification device to the intake side and a second exhaust gas recirculation device that recirculates exhaust gas from the downstream side of the exhaust gas purification device to the intake side are provided.

  When adding fuel for catalyst regeneration, the addition control means determines a unit addition amount, which is the amount of fuel added by one fuel addition, for each control interval. The control interval is a time unit for determining and controlling the amount of fuel added. When the unit addition amount is smaller than the minimum injection amount of the fuel addition unit, the addition control unit performs the fuel addition with the minimum injection amount and the excess fuel amount when the fuel addition is performed with the minimum injection amount. Is reduced from the amount added in subsequent fuel additions. The fuel addition means has a property that the control accuracy of the addition amount is lowered when the addition amount of the fuel is small. Therefore, when the unit addition amount obtained by calculation or the like is smaller than the minimum injection amount, the fuel is added with the minimum injection amount to ensure accuracy. However, in that case, excessive addition will be made in excess of the required amount. Therefore, the addition control means subtracts the excess addition in the next and subsequent fuel additions to obtain an appropriate value for the total addition amount. Adjust so that

The exhaust control device of the internal combustion engine is provided with a temperature sensor for detecting the temperature of the exhaust gas purifier, the control interval is set to a response time of the temperature sensor. Therefore , the fuel addition amount is not calculated in a cycle shorter than the reaction time of the temperature sensor, and an unnecessary load on the ECU is prevented.

  In another aspect of the present invention, an exhaust control device for an internal combustion engine includes an exhaust purification device provided in an exhaust passage of the internal combustion engine, and a fuel addition means provided in an upstream position of the exhaust purification device in the exhaust passage. A first exhaust gas recirculation device that recirculates exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to an intake air side of the internal combustion engine, and an internal combustion engine from a downstream position of the exhaust gas purification device in the exhaust passage. A second exhaust gas recirculation device that recirculates exhaust gas to the intake side of the exhaust gas, and an addition control unit that adds fuel into the exhaust gas using the fuel addition unit, wherein the addition control unit performs one fuel addition Is determined at each control interval, and when the unit addition amount is smaller than the minimum injection amount of the fuel addition means, the addition amount is equal to or greater than the minimum injection amount. Extending the time interval of the fuel addition to perform fuel addition.

  In the exhaust control device for an internal combustion engine described above, an exhaust purification device such as a DPF and a NOx storage reduction catalyst is provided on the exhaust passage. Fuel addition means such as a fuel addition valve is provided upstream of the exhaust purification device. The fuel addition means can add fuel to the exhaust passage for catalyst regeneration such as PM regeneration for the DPF, NOx reduction for the NOx occlusion reduction catalyst, and sulfur poisoning recovery. In addition, a first exhaust gas recirculation device that recirculates exhaust gas from the upstream side of the exhaust gas purification device to the intake side and a second exhaust gas recirculation device that recirculates exhaust gas from the downstream side of the exhaust gas purification device to the intake side are provided.

  When adding fuel for catalyst regeneration, the addition control means determines a unit addition amount, which is the amount of fuel added by one fuel addition, for each control interval. The control interval is a time unit for determining and controlling the amount of fuel added. When the unit addition amount is smaller than the minimum injection amount of the fuel addition unit, the addition control unit extends the fuel addition time interval so that the fuel addition is performed with an addition amount equal to or greater than the minimum injection amount. Thereby, even when the fuel injection amount determined by the catalyst regeneration request is small, it is possible to always ensure the accuracy of the fuel addition amount.

  One aspect of the exhaust control device for an internal combustion engine includes a variation detection means for detecting a variation amount of an exhaust gas recirculation rate by the second exhaust gas recirculation device, wherein the addition control means has the unit addition amount as the fuel addition amount. When the fuel injection amount is equal to or greater than the minimum injection amount of the means and the fluctuation amount of the exhaust gas recirculation rate is larger than the predetermined fluctuation amount, the addition amount is decreased and the fuel addition time interval is shortened. In this aspect, when the added fuel burns in an exhaust purification device such as a catalyst, and the exhaust gas recirculation rate of the exhaust gas recirculation device fluctuates beyond an allowable value, the interval between fuel additions is shortened and the fuel is added little by little. To be added. As a result, fluctuations in the combustion state and torque fluctuations of the internal combustion engine caused by recirculation of the exhaust gas after addition of fuel to the intake side can be suppressed.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Device configuration]
FIG. 1 is a block diagram showing a schematic configuration of an exhaust control device for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals.

  In FIG. 1, an exhaust control device 100 for an internal combustion engine includes an inline 4-cylinder internal combustion engine (hereinafter referred to as “engine”) 10 having first to fourth (# 1 to # 4) cylinders. Each cylinder of the engine 10 is connected to an intake manifold 11 and an exhaust manifold 12. The engine 10 includes a fuel injection valve 15 provided in each cylinder and a common rail 14 that supplies high-pressure fuel to each fuel injection valve 15, and the fuel is in a high-pressure state on the common rail 14 by a fuel pump (not shown). Supplied in. The fuel injection amount and injection timing from the fuel injection valve 15 are controlled by a control signal S4 supplied from the ECU 7.

  In the intake passage 20 connected to the intake manifold 11, there are an air flow meter 21 that measures the amount of air flowing into the engine 10, a throttle valve 22, a compressor 23 a of the turbocharger 23, and an intercooler 24 that cools the intake air. Is provided. The detection signal S1 from the air flow meter 21 is supplied to the ECU 7. The opening degree of the throttle valve 22 is controlled by a control signal S2 supplied from the ECU 7.

  A turbine 23 b of a turbocharger 23 is provided in the exhaust passage 25 connected to the exhaust manifold 12. The upstream position of the turbine 23 b in the exhaust passage 25 and the downstream position from the intercooler 24 in the intake passage 20 are connected by an EGR passage 31. The EGR passage 31 is provided with an EGR valve 33 for controlling the EGR amount. The opening degree of the EGR valve 33 is controlled by a control signal S3 supplied from the ECU 7. The EGR device in which the outlet for EGR gas is located upstream of the turbine of the turbocharger is referred to as a “high pressure loop (HPL) EGR device”.

  A catalyst 36 is provided at a position downstream of the turbine 23 b in the exhaust passage 25. The catalyst 36 can be, for example, a NOx storage reduction catalyst, DPF (Diesel Particulate Filter), or the like. An exhaust throttle valve 41 is provided at a position downstream of the catalyst 36 in the exhaust passage 25. The opening degree of the exhaust throttle valve 41 is controlled by a control signal S7 supplied from the ECU 7. The catalyst 36 is provided with a temperature sensor 42 that detects its temperature. The temperature sensor 42 supplies a detection signal S8 indicating the temperature of the catalyst 36 to the ECU 7.

  Further, an EGR passage 35 that connects a position of the exhaust passage 25 downstream of the turbine 23b and a position of the intake passage 20 upstream of the compressor 23a is provided. More specifically, the EGR passage 35 is configured to extract exhaust gas (EGR gas) from a position downstream of the catalyst 36 provided in the exhaust passage 25. The EGR passage 35 is provided with an EGR valve 37 for controlling the amount of EGR gas and an EGR cooler 39, and the opening degree of the EGR valve 37 is controlled by a control signal S6 from the ECU 7. An EGR device having an EGR gas outlet on the downstream side of the turbine of the turbocharger is referred to as a “low pressure loop (LPL) EGR device”.

  In addition to the fuel injection valve 15 provided for each cylinder, a fuel addition valve 17 for injecting unburned fuel is provided at a position downstream of the turbine 23b in the exhaust passage 25. The amount of fuel added from the fuel addition valve 17 is controlled by a control signal S5 supplied from the ECU 7. The fuel addition valve 17 adds fuel into the exhaust gas mainly for regeneration of the catalyst 36 provided in the exhaust passage. Instead of providing the fuel addition valve at the above position, for example, the fuel addition valve may be provided at a position upstream of the turbine 23b or at the exhaust manifold 12. However, when the exhaust manifold 12 is provided, it is necessary to dispose the fuel addition valve at a position where the fuel added from the fuel addition valve is not recirculated to the intake side by the high-pressure loop EGR device.

  The ECU 7 includes a CPU, a ROM, a RAM, and the like (not shown), and comprehensively controls each element of the exhaust control device 100 for the internal combustion engine as described above.

  In the above configuration, the catalyst 36 corresponds to the exhaust gas purification device in the present invention, and the high-pressure loop EGR device configured by the EGR passage 31 and the like corresponds to the first exhaust gas recirculation device, and the low-pressure configured by the EGR passage 35 and the like. The loop EGR device corresponds to a second exhaust gas recirculation device. The fuel addition valve 17 corresponds to fuel addition means, and the ECU 7 corresponds to addition control means and fluctuation detection means.

  FIG. 2 is an example of a map showing the operation region of the EGR device, and specifically shows the relationship between the engine speed and load and the operation regions of the high-pressure loop EGR device and the low-pressure loop EGR device.

  As shown in the figure, the ECU 7 operates only the high-pressure loop EGR device in a region where the engine speed is low and the engine load is small. On the other hand, in the region where the engine speed is high and the required load is high, the ECU 7 operates only the low-pressure loop EGR device. When the engine speed and the required load are between the operating range of the high pressure loop EGR device and the operating range of the low pressure loop EGR device, the ECU 7 operates both the high pressure loop EGR device and the low pressure loop EGR device. A region where both the high-pressure loop EGR device and the low-pressure loop EGR device are operated simultaneously is referred to as an “MPL (Mixed Pressure Loop) region”. Specifically, the ECU 7 obtains the engine speed using a crank angle sensor (not shown) or the like, and calculates the engine load based on the output of the accelerator opening sensor, the fuel injection amount, and the like. Then, control signals S3 and S6 are supplied to the EGR valves 33 and 37 to control the operations of the high pressure loop EGR device and the low pressure loop EGR device.

[First Embodiment]
Next, a first embodiment of the present invention will be described. In the first embodiment, in the fuel addition for the regeneration process of the catalyst 36, the fuel addition amount from the fuel addition valve 17 is calculated for each control interval determined based on the ability of the ECU 7. The regeneration process of the catalyst 36 includes, for example, PM (particulate matter) regeneration when the catalyst 36 is DPF, and NOx reduction treatment and sulfur poisoning when the catalyst 36 is a NOx storage reduction catalyst. Includes recovery processing.

  First, the calculation period of the fuel addition amount will be described. If the fuel addition amount is calculated for each fuel addition according to a general method, the calculation period of the fuel addition amount per time is shortened, causing a problem that the load on the ECU 7 is increased. For example, the maximum engine speed when fuel is added is 4200 rpm, and the amount of fuel added is calculated 10 times in order to suppress the effects of errors such as calculation errors to 10% or less, and fuel is added every crank angle 720CA. Assume that In this case, the calculation period of the fuel addition amount per fuel addition by the ECU 7 is about 2.8 ms, and the calculation load of the ECU 7 becomes high.

  Therefore, in this embodiment, the concept of the control interval is introduced in the calculation of the fuel addition amount, the fuel addition amount is calculated in units of the control interval, and the fuel addition is controlled. As an example, similar to the above conditions, the maximum engine speed is 4200 rpm, and the fuel addition amount is calculated 10 times in order to suppress the influence of errors such as calculation errors to 10% or less. To do. Here, if the calculation period of the fuel addition amount per time is 16 ms so that the ECU 7 can calculate without excessive load, the control interval is 160 ms.

  Further, the present embodiment is characterized in that the fuel addition amount is changed in consideration of the control accuracy of the fuel injection amount by the fuel addition valve. The fuel addition valve can maintain the control accuracy of the injection amount when injecting more than a certain amount of fuel at one time. However, if the fuel injection amount is too small, the accuracy decreases. It has the property of end up. Hereinafter, the minimum fuel injection amount that can maintain the required accuracy is referred to as “minimum injection amount (Quund)”. The ECU 7 performs fuel addition at the minimum injection amount when the fuel addition amount (hereinafter also referred to as “unit addition amount”) by one fuel addition is smaller than the minimum injection amount of the fuel addition valve 17. At the same time, the surplus injection amount is subtracted from the next fuel addition amount to maintain the total fuel addition amount. Thereby, even when the fuel addition amount per time is small, the addition amount can be controlled with high accuracy.

  The fuel addition amount calculation method according to the present embodiment will be specifically described with reference to FIGS. FIG. 3 is a graph showing an example of changes in the catalyst bed temperature in catalyst regeneration control, and FIG. 4 is a timing chart of fuel addition amount calculation and fuel addition. FIG. 5 is a flowchart of the fuel addition control according to the first embodiment.

  In FIG. 5, first, the ECU 7 determines whether or not there is a regeneration request for the catalyst 36 (step S101). For example, when the catalyst 36 is a NOx storage reduction catalyst, the ECU 7 determines whether there is a request for NOx reduction processing or sulfur poisoning recovery processing. Further, when the catalyst 36 is a DPF or the like, the ECU 7 determines whether PM regeneration is required based on a travel distance of the vehicle, a differential pressure before and after the catalyst, or the like.

  When there is a regeneration request for the catalyst 36 (step S101; Yes), the ECU 7 acquires the target catalyst bed temperature Ttrg and the normal catalyst bed temperature Tcat (step S102). The “target catalyst bed temperature Ttrg” is a target temperature for finally raising the temperature of the catalyst 36 by adding fuel, and the “normal catalyst bed temperature Tcat” is the temperature of the catalyst 36 when fuel is not added. These are determined based on the engine speed of the engine 10 and the fuel injection amount with reference to a map prepared in advance by the ECU 7.

  FIG. 3 shows the relationship between the target catalyst bed temperature Ttrg and the normal catalyst bed temperature Tcat. When the fuel addition is executed, the fuel burns in the catalyst 36 and the catalyst bed temperature rises. That is, in order to raise the catalyst 36 to the target catalyst bed temperature Ttrg, it is necessary to add an amount of fuel corresponding to the temperature deviation (temperature rise amount) ΔT (= Ttrg−Tcat).

  Further, the ECU 7 calculates an amount of gas that passes through the catalyst for catalyst regeneration (hereinafter referred to as “catalyst passing gas amount”) Gcat (step S103). The catalyst passing gas amount Gcat is obtained by the following equation, for example.

Gcat = Ga + Glp + Gf (1)
Here, as shown in FIG. 1, “Ga” is an intake gas amount and is detected by an air flow meter. “Glp” is the amount of EGR gas by the low-pressure loop EGR device, and is calculated based on the opening degree of the EGR valve 37 and the like. “Gf” is the amount of gas supplied to the engine 10.

  Next, the ECU 7 calculates a control interval Ti (step S104). Specifically, the control interval is calculated in consideration of a calculation cycle in which the ECU 7 can perform calculation without excessive load, a maximum engine speed, an allowable error, and the like. In the above example, the maximum number of revolutions of the engine is 4200 rpm, and in order to suppress the influence of errors such as calculation errors to 10% or less, the fuel addition amount is calculated 10 times and fuel addition is performed. If the calculation period of the fuel addition amount per time is 16 ms so that the ECU 7 can calculate without excessive load, the control interval is 160 ms.

  Next, the ECU 7 calculates a unit addition amount (step S105). Now, the required addition amount obtained by one calculation by the ECU 7 is indicated by “Qind”. In this example, the ECU 7 calculates and accumulates the required addition amount Qind 10 times within the control interval Ti, and calculates the accumulated addition amount Qsum in units of the control interval Ti. The required addition amount Qind is obtained by the following equation.

Qind = Gcat × ΔT × K × Kt
= Gcat × (Ttrg−Tcat) × K × Kt (2)
Here, Gcat is obtained by the above formula (1). The coefficient “K” is a coefficient for calculating the injection amount from the temperature difference and the air amount, and is usually a constant regardless of the engine speed. The coefficient “Kt” is a correction coefficient for correcting the amount of heat taken by the piping such as the exhaust passage, and generally varies depending on the exhaust temperature, the engine speed, and the like.

  The ECU 7 repeats the above calculation 10 times every 16 ms to obtain the required addition amount Qind 10 times, integrates them as shown in FIG. 4A, and calculates the integrated addition amount Qsum. Next, the ECU 7 calculates a unit addition amount Qinj that is the amount of fuel actually injected by one addition. As described above, since actual fuel addition is performed at every crank angle 720CA, if the cycle of the crank angle 720CA is X times within a certain control interval Ti, the unit addition amount Qinj is obtained by the following equation.

Qinj = Qsum / X (3)
Thus, the ECU 7 obtains a unit addition amount to be added by one fuel addition. In FIG. 4A, the addition period, which is a period for executing fuel addition, corresponds to the crank angle 720CA, which varies depending on the engine speed, and therefore does not necessarily coincide with the calculation period.

  As described above, in the present invention, the concept of the control interval is introduced, and the fuel addition amount is calculated in the unit. Therefore, it is possible to prevent the calculation load of the ECU 7 from becoming excessively high.

  When the unit addition amount Qinj is calculated by the above equation (3), the ECU 7 determines whether or not the unit addition amount Qinj is larger than the minimum injection amount Qund (step S106). When the unit addition amount Qinj is larger than the minimum injection amount Qund (step S106; Yes), the fuel addition valve 17 can add fuel with the required accuracy, so the ECU 7 adds fuel with the unit addition amount Qinj (step). S107). On the other hand, when the unit addition amount Qinj is smaller than the minimum injection amount Qund (step S106; No), the required accuracy cannot be secured as it is, so the ECU 7 adds fuel at the minimum injection amount Qund (step S108).

  In FIG. 4B, a graph 52 shows the cumulative addition amount of the unit injection amount Qinj, and a graph 51 shows the cumulative addition amount when fuel is added at the minimum injection amount Qund. The difference between the graphs 51 and 52 is the integrated amount of the excess addition amount when the fuel addition is executed with the minimum injection amount Qund. Thus, if fuel addition is performed with the minimum injection amount, the ECU 7 will add more fuel than the unit addition amount obtained by calculation.

  Therefore, when the fuel addition is executed at the minimum injection amount Qund in step S108, the ECU 7 stores the accumulated amount of the surplus addition amount, and adds the fuel by reducing the amount in the next control interval Ti (step S108). S109). Specifically, the ECU 7 subtracts the surplus addition amount from the integrated addition amount Qsum calculated in the next control interval Ti. Thereby, even when the unit addition amount is small, the fuel addition can be executed while ensuring the control accuracy of the fuel addition amount. In the above case, the surplus addition amount is adjusted at the next and subsequent control intervals, and the fuel addition amount corresponding to the required addition amount may not necessarily be added in the control interval unit, but the control interval is There is no problem because it is sufficiently short compared with the rate of change in temperature of the catalyst due to fuel addition.

(First modification)
Next, a first modification of the first embodiment will be described. As described above, the present embodiment is characterized in that the concept of the control interval is introduced in the calculation of the fuel addition amount. In the first embodiment, the control interval is determined based on the calculation capability of the ECU 7. Yes. Instead, in the first modification, the control interval is determined based on the reaction time of the temperature sensor that detects the temperature of the catalyst.

  As described above, the catalyst bed temperature is used when calculating the fuel addition amount. Since the catalyst bed temperature has an individual influence of the engine, the catalyst bed temperature may be corrected based on the temperature detected by the temperature sensor. Here, since the temperature sensor has a reaction time (temperature sensor time constant) from when the catalyst bed temperature changes until it is detected, the control interval is set to a cycle shorter than the temperature sensor time constant. However, even if the amount of fuel added is calculated, there is not much meaning just by applying an unnecessary load to the ECU 7. Therefore, in the first modification, the reaction time (time constant) of the temperature sensor is set as the control interval. As a result, an unnecessary calculation load is not applied to the ECU 7, and a stable fuel addition amount that is corrected by the temperature sensor can be controlled.

  Note that the first modification is different from the first embodiment described above only in the control interval determination method, and the other points are the same. Therefore, also in the flowchart shown in FIG. 5, only the method of determining the control interval in step S104 is different, and the other processes are the same.

(Second modification)
Next, a second modification of the first embodiment will be described. In the first embodiment, the control interval is determined based on the calculation capability of the ECU 7. Instead, in the second modification, the time until the fuel added from the fuel addition valve 17 actually reaches the catalyst 36 is set as a control interval.

  In order for the fuel added from the fuel addition valve 17 to actually reach the catalyst 36, a time corresponding to the path length or the like (hereinafter referred to as “added fuel arrival time”) is required. Therefore, even if the control interval is set to a period shorter than the addition fuel arrival time, there is not much meaning only to apply an unnecessary load to the ECU 7. Therefore, in the second modification, the addition fuel arrival time is set as the control interval. Thus, an appropriate amount of fuel can be added without applying unnecessary calculation load to the ECU 7.

  Specifically, the addition fuel arrival time is determined based on the structural volume from the fuel addition valve 17 to the catalyst 36, the amount of gas recirculated to the intake side by the low pressure loop EGR device, and the like. As illustrated in FIG. 2, since the EGR amount by the low-pressure loop EGR device varies depending on the engine speed and load, the control interval also varies depending on the engine speed and load.

  In the configuration shown in FIG. 1, the fuel addition valve 17 is provided on the exhaust passage 25 at a position downstream of the turbine 23b of the turbocharger 23. Instead, the fuel addition valve 17 is provided on the exhaust passage 25 and on the turbine 23b. It is good also as a structure provided in the upstream position of this, or the exhaust manifold 12. FIG. Even in that case, only the structural volume from the fuel addition valve 17 to the catalyst 36 changes, and the addition fuel arrival time may be calculated in the same manner as described above to determine the control interval.

  The second modification differs from the second embodiment described above only in the control interval determination method, and is otherwise the same. Therefore, also in the flowchart shown in FIG. 5, only the method of determining the control interval in step S104 is different, and all other processes are the same.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, the amount and timing of fuel addition for catalyst regeneration are controlled in consideration of the amount of gas recirculated to the intake side by the low-pressure loop EGR device. In the second embodiment, the unit addition amount is calculated in units of control intervals.

As shown in FIG. 1, in the configuration in which the exhaust outlet of the low pressure loop EGR device is provided downstream of the fuel addition valve 17, the added fuel and carbon dioxide (CO ₂ ) generated when the fuel burns with the catalyst. Etc. are returned to the intake side by the low-pressure loop EGR device, and therefore phenomena such as fluctuation of the combustion state of the engine and fluctuation of torque may occur.

  Here, from the viewpoint of the influence on the combustion state and torque fluctuation of the engine, first, the larger the ratio of gas returned to the intake side by the low-pressure loop EGR device (that is, the EGR rate), the larger the influence on the combustion state and torque fluctuation. Becomes larger. In addition, the greater the amount of fuel added by one fuel addition, the greater the variation in engine combustion and torque. That is, when adding the same amount of fuel in total, it is better to reduce the amount added once and add in multiple times than to increase the amount added once and add less. Variations are less likely to occur.

  Therefore, in the present embodiment, the EGR rate of the low-pressure loop EGR device is monitored, and when the EGR rate exceeds a predetermined allowable value, the fuel addition time interval is shortened to suppress combustion fluctuation. However, when the unit addition amount per one time is smaller than the minimum injection amount of the fuel addition valve 17, in order to ensure the control accuracy of the injection amount, the one fuel addition amount is made larger than the minimum injection amount. Increase the time between fuel additions.

  FIG. 6 is a flowchart of fuel addition control according to the second embodiment. In FIG. 6, steps S201 to S206 are the same as steps S101 to S106 in the fuel addition control of the first embodiment shown in FIG.

  In step S206, when the unit addition amount, which is the fuel addition amount per time, is smaller than the minimum injection amount of the fuel addition valve 17 (step S206; No), the ECU 7 extends the fuel addition time interval to increase the addition amount. Is increased (step S209). More specifically, the fuel addition time interval is extended so that the fuel addition amount exceeds the minimum injection amount. Since the basic fuel addition period is a crank angle 720CA as shown in FIG. 4A, for example, the fuel addition time interval is extended by one cycle of the crank angle (= 360 CA) to obtain a crank angle 1080CA. And If the fuel addition amount still does not exceed the minimum injection amount even if one cycle is extended, the fuel addition time interval may be further extended by one cycle. In this way, fuel addition is prevented from being performed at less than the minimum injection amount, and control accuracy of the fuel addition amount is ensured.

  On the other hand, when the unit addition amount is larger than the minimum injection amount in step S206 (step S206; Yes), first, the ECU 7 passes through the low pressure loop EGR device based on the opening degree of the EGR valve 37, the intake air temperature, and the like. (EGR gas amount) Glp is calculated (step S207). The EGR gas amount Glp may be detected using a gas flow meter or the like.

  Next, the ECU 7 calculates an EGR rate (also referred to as “LPL-EGR rate”) of the low-pressure loop EGR device based on the calculated EGR gas amount Glp (step S208). Specifically, the LPL-EGR rate is obtained by the following equation.

LPL-EGR rate = Glp / Gcyl (4)
As shown in FIG. 1, “Gcyl” is the amount of intake gas of the engine and is obtained by the following equation.

Gcyl = Ga + Ghp + Glp (5)
Thus, when the LPL-EGR rate is obtained, the ECU 7 determines whether or not the fluctuation of the LPL-EGR rate is within a predetermined allowable value (step S210). The LPL-EGR rate fluctuates due to the generation of CO ₂ by the catalyst by adding fuel. When the variation of the LPL-EGR rate is within the allowable value (step S210; Yes), the ECU 7 performs fuel addition with the unit addition amount. On the other hand, when the fluctuation of the LPL-EGR rate exceeds the allowable value (step S210; No), the ECU 7 shortens the fuel addition time interval and decreases the fuel addition amount at one time to perform fuel addition (step S212). ). Specifically, the fuel addition time interval is shortened by one cycle of crank angle (= 360 CA) to 360 CA. Thus, when the variation of the LPL-EGR rate exceeds the allowable value, the small amount of fuel is added many times to suppress the variation of the combustion state caused by the low pressure loop EGR device.

As described above, according to the second embodiment, the fuel addition amount required for the catalyst regeneration is ensured in consideration of the EGR amount by the low-pressure loop EGR device, and the combustion state fluctuation caused by the wraparound of CO ₂ . Torque fluctuation can be suppressed.

1 is a schematic block diagram of an exhaust control device for an internal combustion engine according to an embodiment. The map of an EGR area | region is shown. It is a graph which shows the example of a change of the catalyst bed temperature in the regeneration control of a catalyst. It is a timing chart of calculation of fuel addition amount and fuel addition. It is a flowchart of the fuel addition control by 1st Embodiment. It is a flowchart of fuel addition control by 2nd Embodiment.

Explanation of symbols

7 ECU
DESCRIPTION OF SYMBOLS 10 Engine 15 Fuel injection valve 17 Fuel addition valve 20 Intake passage 23 Turbocharger 25 Exhaust passage 31, 35 EGR passage 36 Catalyst 33, 37 EGR valve

Claims (3)

An exhaust control device for an internal combustion engine,
An exhaust purification device provided in an exhaust passage of the internal combustion engine;
Fuel addition means provided at an upstream position of the exhaust purification device in the exhaust passage;
A first exhaust gas recirculation device for recirculating exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
A second exhaust gas recirculation device that recirculates exhaust gas from the downstream side position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
A temperature sensor for detecting a temperature of the exhaust purification device;
Addition control means for adding fuel into the exhaust using the fuel addition means,
The addition control means determines a unit addition amount, which is an amount of fuel added by one fuel addition, for each control interval set in a reaction time of the temperature sensor, and the unit addition amount is the fuel addition amount. When the fuel injection is smaller than the minimum injection amount of the means, the fuel addition is performed at the minimum injection amount, and the excess fuel amount when the fuel addition is performed at the minimum injection amount is reduced from the addition amount in the subsequent fuel addition. An exhaust control device for an internal combustion engine. An exhaust control device for an internal combustion engine,
An exhaust purification device provided in an exhaust passage of the internal combustion engine;
Fuel addition means provided at an upstream position of the exhaust purification device in the exhaust passage;
A first exhaust gas recirculation device for recirculating exhaust gas from an upstream position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
A second exhaust gas recirculation device that recirculates exhaust gas from the downstream side position of the exhaust gas purification device in the exhaust passage to the intake side of the internal combustion engine;
Addition control means for adding fuel into the exhaust using the fuel addition means,
The addition control means determines a unit addition amount that is the amount of fuel added by one fuel addition for each control interval, and when the unit addition amount is smaller than the minimum injection amount of the fuel addition means, An exhaust control device for an internal combustion engine, wherein a fuel addition time interval is extended so that fuel is added with an addition amount equal to or greater than the minimum injection amount. Fluctuation detecting means for detecting a fluctuation amount of the exhaust gas recirculation rate by the second exhaust gas recirculation device,
When the unit addition amount is equal to or greater than the minimum injection amount of the fuel addition unit and the fluctuation amount of the exhaust gas recirculation rate is larger than a predetermined fluctuation amount, the addition control means reduces the addition amount and adds fuel. The exhaust gas control apparatus for an internal combustion engine according to claim 2 , wherein the time interval is shortened.

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