JP2007309147A - Diesel engine exhaust purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of a diesel engine efficiently performing rich spike with less fuel. <P>SOLUTION: Presence of a demand for rich spike is determined in deceleration of the diesel engine 10 (steps 100, 102). When rich spike is demanded, valve timing of an exhaust valve 56 is advanced to make exhaust valve closing timing early (step 104). Fuel is injected into a cylinder from an injector (step 106) and is burned in the cylinder. When fuel is short of a fuel quantity required for the rich spike, fuel is applied to an exhaust system (step 108). A large pumping loss is caused by the advancing of the exhaust valve closing timing to countervail positive torque caused by the combustion of fuel in the cylinder, thereby enabling generation of desired engine brake force. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for a diesel engine.

  In a diesel engine (compression ignition internal combustion engine), since a large amount of oxygen is usually contained in exhaust gas, NOx cannot be purified by a three-way catalyst. Therefore, NOx in the exhaust gas is stored by using a NOx storage reduction catalyst, DPNR (Diesel Particulate-NOx-Reduction system), etc. (hereinafter collectively referred to as “NOx catalyst”). An exhaust purification system is used.

  In order for the NOx catalyst to efficiently store NOx, the temperature of the NOx catalyst needs to be within a certain range. During fuel cut at the time of deceleration or the like, high-temperature burned gas does not flow through the exhaust passage, so the NOx catalyst is likely to be cooled to a temperature lower than the above temperature range. When the NOx catalyst cools, NOx blows downstream of the NOx catalyst after returning from the fuel cut.

  Japanese Patent Application Laid-Open No. 2003-83054 discloses an exhaust emission control device that performs catalyst heat retention control in order to prevent the temperature of the NOx catalyst from decreasing when the fuel is cut. The catalyst heat retention control is control for adding fuel into the exhaust gas from a fuel addition valve provided in the exhaust system. When this catalyst heat retention control is performed, the fuel added to the exhaust gas reacts (combusts) with the NOx catalyst, thereby preventing a temperature drop of the NOx catalyst.

JP 2003-83054 A JP 2002-227672-A JP 2004-116393 A JP 2002-38932 A JP 2006-9638 A

By the way, NOx occluded in the NOx catalyst can be reduced and purified to N ₂ and released by performing a rich spike in which the exhaust air-fuel ratio is temporarily made rich below the stoichiometric air-fuel ratio. Since there is a limit to the amount of NOx that can be stored in the NOx catalyst, it is sometimes necessary to perform this rich spike in a system equipped with the NOx catalyst.

  In the above-described conventional technology, only the heat retention control of the NOx catalyst is performed during fuel cut during deceleration or the like, and rich spike is performed during normal operation (see paragraphs 0045 to 0053 of the above publication).

  On the other hand, according to the knowledge of the present inventors, it is considered that the fuel efficiency can be improved by performing the rich spike at the time of deceleration of the diesel engine. In other words, since it is not necessary to output a positive torque during deceleration, the intake air amount can be reduced. If the amount of intake air decreases, the amount of fuel required to make the exhaust air / fuel ratio equal to or lower than the stoichiometric air / fuel ratio required for the rich spike can be reduced. Therefore, when the rich spike is performed by adding fuel to the exhaust gas from an exhaust system fuel addition valve or the like during deceleration of the diesel engine, the amount of fuel required for the rich spike can be reduced. That is, fuel consumption performance can be improved.

  However, when the rich spike is performed at the time of deceleration, the following problems are considered to occur. The first problem is the reduced effectiveness of the rich spike due to the abundance of oxygen. At the time of deceleration, fuel cut is usually performed, so the gas discharged from the diesel engine is air itself. In the NOx catalyst into which the gas with the fuel added to the air flows, a large amount of oxygen is locally present even if the air-fuel ratio is rich as a whole. In such a case, the oxygen preferentially reacts with a reducing agent such as HC, so that the stored NOx hardly reacts with the reducing agent. As a result, the effectiveness of the rich spike becomes worse.

  The second problem is a reduction in the effectiveness of the rich spike due to a decrease in the temperature of the NOx catalyst. Even when NOx occluded in the NOx catalyst is reduced and purified by a rich spike, in order to obtain a high purification rate, the NOx catalyst needs to be within a certain temperature range. At the time of deceleration, since low-temperature air flows through the NOx catalyst, the temperature of the NOx catalyst is abruptly lowered and is likely to be cooled to a temperature lower than the temperature range. When the temperature of the NOx catalyst decreases in this way, the effectiveness of the rich spike becomes worse.

  The third problem is the occurrence of HC poisoning. When air containing unburned fuel flows into the NOx catalyst having a low temperature, the active surface of the catalyst surface is covered with HC, and the activity of the NOx catalyst is reduced. This is called HC poisoning. When HC poisoning occurs, the effectiveness of the rich spike is reduced, or the NOx occlusion ability after the end of the rich spike is reduced.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an exhaust emission control device for a diesel engine that can efficiently perform a rich spike with a small amount of fuel.

In order to achieve the above object, a first invention is an exhaust emission control device for a diesel engine,
It is provided in the exhaust passage of a diesel engine and has a function of storing NOx in an atmosphere where the air-fuel ratio is greater than the stoichiometric air-fuel ratio, and reducing and purifying the stored NOx in an atmosphere where the air-fuel ratio is less than the stoichiometric air-fuel ratio. NOx catalyst,
A variable valve mechanism that makes at least the closing timing of the exhaust valve of the diesel engine variable;
When decelerating the diesel engine, when decelerating rich spike request determining means for determining whether or not to perform decelerating rich spike control that temporarily sets the air-fuel ratio of the exhaust gas flowing into the NOx catalyst to be equal to or lower than the stoichiometric air-fuel ratio;
First fuel injection means capable of injecting fuel into the working gas so as to burn in the cylinder of the diesel engine;
Second fuel injection means capable of injecting fuel into the working gas so as not to burn in the cylinder of the diesel engine;
Both injections when the first and second fuel injection means inject the required fuel injection amount necessary for setting the exhaust air-fuel ratio to the target air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio when executing the rich spike control during deceleration Injection distribution determining means for determining the distribution of the quantity;
When the deceleration rich spike control is performed, the exhaust valve closes before top dead center so that the combustion gas is compressed in the cylinder so that the diesel engine can generate a braking force. Exhaust valve advance means for controlling the variable valve mechanism to advance the exhaust valve closing timing;
It is characterized by providing.

The second invention is the first invention, wherein
The injection distribution determining unit determines a fuel injection amount of the first fuel injection unit when the rich spike control at the time of deceleration is performed as a fuel injection amount that provides a predetermined feeling of deceleration, and the requested fuel injection amount The amount not enough is distributed to the second fuel injection means.

The third invention is the first or second invention, wherein
The injection distribution determining unit increases the distribution of the fuel injection amount to the first fuel injection unit as the advancement degree of the exhaust valve closing timing at the time of execution of the deceleration rich spike control is larger. .

According to a fourth invention, in any one of the first to third inventions,
An exhaust system temperature acquisition means for detecting or estimating the exhaust system temperature;
The exhaust valve advance means increases the advance angle of the exhaust valve closing timing at the time of execution of the deceleration rich spike control as the exhaust system temperature is lower,
The injection distribution determining unit increases the distribution of the fuel injection amount to the first fuel injection unit as the exhaust system temperature is lower.

According to a fifth invention, in any one of the first to fourth inventions,
Exhaust system temperature acquisition means for detecting or estimating the exhaust system temperature;
Injection timing delay means for delaying the injection timing of the first fuel injection means at the time of execution of the deceleration rich spike control as the exhaust system temperature is lower;
Is further provided.

According to a sixth invention, in any one of the first to fifth inventions,
The variable valve mechanism is one that makes the opening timing of the exhaust valve variable,
The exhaust valve advance means advances the exhaust valve opening timing as well as the exhaust valve closing timing when the rich spike control at the time of deceleration is executed.

According to a seventh invention, in any one of the first to sixth inventions,
An intake throttle valve disposed in the intake passage of the diesel engine;
A deceleration air amount reduction means for reducing the intake air amount by reducing the opening of the intake throttle valve as compared with the non-deceleration when executing the rich spike control during deceleration;
Is further provided.

  According to the first invention, when the diesel engine is decelerated, it is possible to perform deceleration rich spike control that temporarily sets the air-fuel ratio of the exhaust gas flowing into the NOx catalyst to be equal to or less than the theoretical air-fuel ratio. By performing the rich spike at the time of deceleration, the rich spike can be performed with a small amount of fuel, and the fuel efficiency can be improved. In addition, when performing rich spike control at the time of deceleration, by performing fuel injection that burns in the cylinder, the amount of oxygen flowing into the NOx catalyst can be reduced, and the NOx catalyst can be kept at a temperature suitable for the rich spike. Can do. For this reason, it is possible to avoid the effect of rich spikes and HC poisoning, and to perform rich spikes with high efficiency. Furthermore, according to the first aspect of the invention, when the rich spike control at the time of deceleration is executed, a large pumping loss is generated by advancing the exhaust valve closing timing, so that the engine brake is caused by the combustion of fuel in the cylinder. It is possible to reliably avoid a situation in which the effectiveness of is reduced. That is, it is possible to surely obtain the desired feeling of deceleration.

  According to the second invention, when the rich spike control at the time of deceleration is executed, the fuel injection amount that is combusted in the cylinder is determined as the fuel injection amount that provides a predetermined feeling of deceleration, and the required fuel injection amount It is possible to distribute the amount that is insufficient for fuel injection that is not burned in the cylinder. As a result, as long as a predetermined feeling of deceleration is obtained, the amount of fuel injection for burning in the cylinder can be increased. For this reason, the effectiveness of the rich spike is further improved, and the rich spike can be performed with higher efficiency.

  According to the third aspect of the invention, the larger the advancement degree of the exhaust valve closing timing during execution of the deceleration rich spike control, the greater the distribution of the fuel injection amount for combustion in the cylinder. As the advance angle of the exhaust valve closing timing is larger, a larger pumping loss can be generated. For this reason, according to the third invention, it is possible to increase the distribution of the fuel injection amount for combustion in the cylinder while ensuring the desired engine braking force. Therefore, the effect of rich spike can be further improved.

  According to the fourth aspect of the invention, the lower the exhaust system temperature, the larger the advance angle of the exhaust valve closing timing when the rich spike control at the time of deceleration is performed, and the distribution of the fuel injection amount for combustion in the cylinder. Can do a lot. Thus, the exhaust temperature can be increased as the exhaust system temperature is lower. For this reason, it is possible to ensure that the temperature of the NOx catalyst enters the optimal temperature range when executing the rich spike control during deceleration. Therefore, rich spike can be performed with higher efficiency.

  According to the fifth aspect of the invention, the lower the exhaust system temperature, the higher the exhaust temperature can be delayed by delaying the injection timing of the in-cylinder combustion fuel. For this reason, it is possible to ensure that the temperature of the NOx catalyst enters the optimal temperature range when executing the rich spike control during deceleration. Therefore, rich spike can be performed with higher efficiency.

  According to the sixth invention, when the rich spike control at the time of deceleration is executed, the exhaust valve opening timing can be advanced together with the exhaust valve closing timing. As a result, the exhaust valve can be opened during the expansion stroke to reduce the expansion work of the combustion gas. Therefore, the desired engine braking force can be generated more reliably.

  According to the seventh aspect, the intake air amount can be reduced when the rich spike control during deceleration is executed. For this reason, the amount of fuel required for the rich spike, that is, the amount of fuel required to make the air-fuel ratio of the exhaust gas flowing into the NOx catalyst equal to or lower than the stoichiometric air-fuel ratio can be reduced. Therefore, fuel can be saved and fuel efficiency can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system shown in FIG. 1 includes a four-cycle diesel engine (compression ignition internal combustion engine) 10. It is assumed that the diesel engine 10 is mounted on a vehicle and used as a power source. Although the illustrated diesel engine 10 is an in-line four-cylinder type, in the present invention, the number of cylinders and the cylinder arrangement are not limited thereto.

  Each cylinder of the diesel engine 10 is provided with an injector 12 that injects fuel directly into the cylinder. The injectors 12 of each cylinder are connected to a common common rail 14. Fuel in a fuel tank (not shown) is pressurized to a predetermined fuel pressure by a supply pump 16, stored in the common rail 14, and supplied from the common rail 14 to each injector 12. The injector 12 can inject the fuel into the cylinder at an arbitrary timing a plurality of times during one cycle.

  An exhaust passage 18 of the diesel engine 10 is branched by an exhaust manifold 20 and connected to an exhaust port 22 (see FIG. 2) of each cylinder. The diesel engine 10 according to this embodiment includes a turbocharger 24. The exhaust passage 18 is connected to the exhaust turbine of the turbocharger 24.

  A NOx catalyst 26 is provided downstream of the turbocharger 24 in the exhaust passage 18. The NOx catalyst 26 occludes NOx in the exhaust gas in an atmosphere where the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, in an atmosphere leaner than the stoichiometric air-fuel ratio, and in the atmosphere where the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio, that is, the stoichiometric air-fuel ratio. In the following rich atmosphere, it has a function of reducing and purifying the stored NOx and reducing it. The NOx catalyst 26 may have only a function of storing and reducing NOx, or may be a DPNR (Diesel Particulate-NOx-Reduction system) having a function of collecting soot in exhaust gas. The NOx catalyst 26 may also have a function other than collecting soot.

  An air cleaner 30 is provided near the inlet of the intake passage 28 of the diesel engine 10. The air drawn through the air cleaner 30 is compressed by the intake compressor of the turbocharger 24 and then cooled by the intercooler 32. The intake air that has passed through the intercooler 32 is distributed by the intake manifold 34 to the intake ports 35 (see FIG. 2) of the respective cylinders.

  An intake throttle valve 36 is installed between the intercooler 32 and the intake manifold 34 in the intake passage 28. Further, an air flow meter 38 for detecting the amount of intake air is installed in the vicinity of the intake passage 28 downstream of the air cleaner 30.

  One end of an external EGR passage 40 is connected to the intake passage 28 in the vicinity of the intake manifold 34. The other end of the external EGR passage 40 is connected to the vicinity of the exhaust manifold 20 of the exhaust passage 18. In this system, a part of the exhaust gas (burned gas) can be recirculated to the intake passage 28 through the external EGR passage 40, that is, external EGR (Exhaust Gas Recirculation) can be performed.

  In the middle of the external EGR passage 40, an EGR cooler 42 for cooling the external EGR gas is provided. An EGR valve 44 is provided downstream of the EGR cooler 42 in the external EGR passage 40. As the opening degree of the EGR valve 44 is increased, the amount of exhaust gas passing through the external EGR passage 40, that is, the amount of external EGR can be increased. Further, the external EGR amount and the external EGR rate can be adjusted not only by the opening degree of the EGR valve 44 but also by the opening degree of the intake throttle valve 36.

  In addition, the present system includes an intake pressure sensor 46 that detects intake pressure, an accelerator position sensor 48 that detects the amount of depression (accelerator position) of an accelerator pedal of a vehicle on which the diesel engine 10 is mounted, and exhaust gas. A fuel addition valve 66 for injecting fuel and a catalyst temperature sensor 68 for detecting the bed temperature of the NOx catalyst 26 are provided. The intake pressure sensor 46 is disposed in the intake passage 28 on the downstream side of the intake throttle valve 36. The fuel addition valve 66 is installed in the exhaust passage 18 upstream of the NOx catalyst 24 and downstream of the turbocharger 24.

  Furthermore, the system of the present embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is connected to the various sensors and actuators described above. ECU50 controls the driving | running state of the diesel engine 10 by operating each actuator according to a predetermined program based on the signal from each sensor.

  FIG. 2 is a view showing a cross section of one cylinder of the diesel engine 10 in the system shown in FIG. Hereinafter, the diesel engine 10 will be further described. As shown in FIG. 2, a crank angle sensor 62 that detects the rotation angle (crank angle) of the crankshaft 60 is attached in the vicinity of the crankshaft 60 of the diesel engine 10. The crank angle sensor 62 is connected to the ECU 50. According to the signal from the crank angle sensor 62, the engine speed and the like can be detected.

  Further, the diesel engine 10 is provided with a variable exhaust valve mechanism 58 that continuously varies the phase of a cam that drives the exhaust valve 56. According to the exhaust variable valve mechanism 58, the valve opening phase of the exhaust valve 56 can be continuously changed. Note that a variable valve mechanism may also be provided on the intake valve 52 side.

  FIG. 3 is a diagram illustrating an example of valve lifts of the intake valve 52 and the exhaust valve 56 in the diesel engine 10. The thin solid lines in FIG. 3 are valve lift diagrams of the intake valve 52 and the exhaust valve 56 during normal control. On the other hand, the thick solid line in FIG. 3 is a valve lift diagram of the exhaust valve 56 when the valve opening phase of the exhaust valve 56 is advanced. Thus, according to the exhaust variable valve mechanism 58, the valve timing of the exhaust valve 56 is advanced (accelerated), and the closing timing of the exhaust valve 56 (hereinafter referred to as "exhaust valve closing timing"). It can be made before the top dead center (TDC).

  In the exhaust variable valve mechanism 58 of the present embodiment, the opening timing of the exhaust valve 56 (hereinafter referred to as “exhaust valve opening timing”) is advanced by the same amount as the exhaust valve closing timing advances. .

  The specific configuration of the exhaust variable valve mechanism 58 in the present invention is not limited to the cam phase variable mechanism, and any configuration may be used as long as the exhaust valve closing timing is variable. For example, the exhaust variable valve mechanism 58 may be configured by an electromagnetically driven valve or a hydraulically driven valve that can open and close the exhaust valve 56 at an arbitrary timing. Further, as shown by the broken line in FIG. 3, the variable exhaust valve mechanism 58 may be composed of a variable operating angle mechanism that continuously varies only the exhaust valve closing timing without changing the exhaust valve opening timing. Good.

[Features of Embodiment 1]
In the present invention, rich spike control for reducing and purifying NOx occluded in the NOx catalyst 26 is performed during deceleration of the diesel engine 10 (hereinafter simply referred to as “deceleration”). In the present specification, the rich spike control of the present invention performed at the time of deceleration is referred to as “decelerated rich spike control”.

  During deceleration, there is no need to output torque (positive torque), so the amount of intake air can be reduced by reducing the opening of the intake throttle valve 36. Therefore, during deceleration, the amount of fuel required for the rich spike, that is, the amount of fuel required to bring the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 26 below the stoichiometric air-fuel ratio is small. For this reason, fuel can be saved and fuel efficiency can be improved.

  At the time of deceleration, generally, control for stopping fuel injection (injection that becomes torque) from the injector 12 for burning in the cylinder, that is, fuel cut is performed. When the rich spike is performed at the time of deceleration, the fuel cut is performed, and when all the required fuel amount is injected from the fuel addition valve 66, the effect of the rich spike is reduced or the HC is reduced as described above. There is a problem that poisoning occurs.

  Therefore, in this embodiment, when performing rich spike control at the time of deceleration, fuel cut is prohibited and fuel injection from the injector 12 for burning in the cylinder is performed. Thereby, since the amount of oxygen in the exhaust gas can be reduced, it is possible to surely prevent the effect of the rich spike due to the presence of abundant oxygen. Further, by continuing the combustion in the cylinder, the high-temperature exhaust gas can flow into the NOx catalyst 26. For this reason, it is possible to reliably prevent the effect of the rich spike from being reduced or the HC poisoning from occurring due to the excessive cooling of the NOx catalyst 26.

  As described above, when the fuel injection from the injector 12 for burning in the cylinder at the time of deceleration is performed, if the valve timing of the exhaust valve 56 is the same as that in the normal control, the effectiveness of the engine brake is deteriorated. Furthermore, there is a disadvantage that the diesel engine 10 generates a positive torque. Therefore, in the present embodiment, during rich spike control during deceleration, the valve timing of the exhaust valve 56 is advanced as shown by the thick solid line in FIG. When the valve timing of the exhaust valve 56 is advanced, the exhaust valve 56 is closed before top dead center, and the combustion gas (burned gas) is compressed in the cylinder. For this reason, a large pumping loss occurs in the compression stroke. By increasing the pumping loss, the positive torque generated in the expansion stroke can be canceled out, so that the engine brake can be reliably generated. Therefore, it is possible to reliably satisfy the feeling of deceleration expected from the driver.

  In the present embodiment, the exhaust valve opening timing is also advanced with the advancement of the exhaust valve closing timing. Thereby, since the exhaust valve 56 opens in the middle of the expansion stroke, the expansion work of the combustion gas can be reduced. Therefore, the required engine braking force can be generated more reliably.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is repeatedly executed every predetermined time. According to the routine shown in FIG. 4, it is first determined whether or not the vehicle is decelerating (step 100). Specifically, when the accelerator opening is zero and the engine speed is greater than or equal to a predetermined value, it is determined that the diesel engine 10 is in a decelerating state.

  If it is determined in step 100 that the vehicle is not decelerating, the current processing cycle is terminated as it is. On the other hand, if it is determined that the vehicle is decelerating, it is next determined whether or not a rich spike is necessary (step 102). The determination method is not particularly limited, and can be performed by a known method. For example, the relationship between the operating state of the diesel engine 10 and the NOx emission amount is stored in the ECU 50 as a map, and the amount of NOx flowing into the NOx catalyst 26 after the previous rich spike is integrated according to the map, When the integrated value exceeds a predetermined value, it can be determined that a rich spike is necessary.

  If it is determined in step 102 that a rich spike is not necessary, the current processing cycle is terminated as it is. On the other hand, when it is determined that the rich spike is necessary, deceleration rich spike control is executed as described below.

  That is, first, the valve timing of the exhaust valve 56 is advanced as illustrated in FIG. 3 (step 104). At this time, in this embodiment, the valve timing of the exhaust valve 56 is advanced to a predetermined position. Hereinafter, the degree of advance (advance amount) of the valve timing (exhaust valve close timing) of the exhaust valve 56 is referred to as “advance angle”. Further, in step 104, it is assumed that a process for making the opening degree of the intake throttle valve 36 smaller than that during non-deceleration is also performed. Thereby, the amount of intake air can be reduced.

  Subsequent to the process in step 104, fuel injection from the injector 12 into the cylinder is executed (step 106). The fuel injection here refers to fuel injection performed by burning the fuel in the cylinder. This fuel injection may be performed in a plurality of times in one cycle. For example, the main injection and the pilot injection that precedes the main injection may be performed separately.

  The fuel injection amount in step 106 (the total amount when it is divided into a plurality of times) is set in advance as an amount that provides a predetermined feeling of deceleration. That is, in consideration of the positive torque generated by the combustion gas performing the expansion work and the negative torque due to the pumping loss caused by the advance angle (early closing) of the exhaust valve 56, the diesel engine 10 has the desired braking force. The fuel injection amount is set so as to exhibit.

  The pumping loss, that is, the pumping loss caused by the combustion gas being compressed in the cylinder, increases as the advance angle of the exhaust valve 56 increases. For this reason, the fuel injection amount in step 106 can be increased as the advance angle of the exhaust valve 56 increases.

  When determining the fuel injection amount in step 106, correction may be performed based on other information such as the engine speed.

  Subsequent to the process of step 106, a process of adding fuel into the exhaust gas from the fuel addition valve 66 is executed (step 108). Here, an amount of fuel necessary for making the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 26 coincide with the target air-fuel ratio for rich spike (a value equal to or lower than the theoretical air-fuel ratio) is injected from the fuel addition valve 66. . That is, by subtracting the fuel injection amount in step 106 from the required fuel injection amount calculated from the intake air amount detected by the air flow meter 38 and the target air-fuel ratio, the injection from the fuel addition valve 66 in this step 108 is performed. The amount of fuel to be calculated can be calculated.

  By the processing as described above, the rich spike control at the time of deceleration according to the present embodiment can be performed. According to the rich spike control at the time of deceleration, the rich spike can be completed in a state where the intake air amount is reduced. Therefore, the amount of fuel necessary to make the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 26 the target air-fuel ratio is reduced. Less is enough. For this reason, rich spike can be performed with a small amount of fuel, and fuel efficiency can be improved.

  Further, according to the rich spike control at the time of deceleration, the fuel injection is performed so that the fuel is burned in the cylinder without performing the fuel cut. Reduction of spike effectiveness and occurrence of HC poisoning can be reliably avoided. That is, the amount of oxygen flowing into the NOx catalyst 26 can be reduced, and the temperature of the NOx catalyst 26 can be reliably prevented from becoming too low. For this reason, the NOx occluded in the NOx catalyst 26 can be efficiently reduced and purified and released. And HC poisoning resulting from the temperature fall of the NOx catalyst 26 does not occur.

  Further, according to the rich spike control at the time of deceleration, since a large pumping loss is generated by advancing the valve timing of the exhaust valve 56, the positive torque generated by burning the fuel in the cylinder is offset. be able to. For this reason, it is possible to surely prevent the engine brake from being deteriorated, and it is possible to reliably obtain a desired feeling of deceleration.

  In the first embodiment described above, both the closing timing and the opening timing of the exhaust valve 56 are advanced in the step 104. However, in the present invention, at least the exhaust valve closing timing should be advanced. . That is, it is not necessary to advance the exhaust valve opening timing.

  In the present invention, when the rich spike control at the time of deceleration is executed, the fuel injection amount at the above step 106 or the above is based on the output of an air-fuel ratio sensor (oxygen sensor) (not shown) provided before or after the NOx catalyst 26. Air-fuel ratio feedback control for correcting the fuel injection amount in step 108 may be performed.

  In the first embodiment described above, in step 108, fuel is injected using the fuel addition valve 66. However, the fuel injection here may be performed so as not to burn in the cylinder. Any method can be used as long as it is possible. For example, the fuel injection in step 108 may be performed by post injection in which fuel is injected from the injector 12 after combustion in the cylinder is completed.

  Further, when the target air-fuel ratio for rich spike can be achieved only by the fuel injection in step 106, the fuel injection amount in step 108 may be made zero. For example, if the air-fuel ratio is enriched and the combustion temperature is lowered by performing a large amount of EGR, in-cylinder combustion can be performed at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio without discharging smoke. If such in-cylinder combustion is possible, the deceleration rich spike control of the present invention can be performed even if the fuel injection amount in step 108 is zero.

  In the first embodiment described above, the NOx catalyst 26 is the “NOx catalyst” in the first invention, and the exhaust variable valve mechanism 58 is the “variable valve mechanism” in the first and sixth inventions. , Respectively. Further, when the ECU 50 executes the processing of the steps 100 and 102, the “deceleration rich spike request determining means” in the first invention executes the processing of the step 106, thereby executing the processing in the first invention. When the “first fuel injection means” executes the processing of step 108, the “second fuel injection means” according to the first aspect of the invention executes the processing of steps 106 and 108. The “injection distribution determining means” in the first and second inventions executes the process of step 104, and the “exhaust valve advancement means” in the first and sixth inventions executes the process of step 104. Thus, the “deceleration air amount reduction means” in the seventh aspect of the invention is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 5 and FIG. 6. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit. The present embodiment can be realized using the same hardware configuration as that of the first embodiment.

[Features of Embodiment 2]
At the time of execution of the rich spike control at the time of deceleration, as described above, as the advance angle of the exhaust valve 56 is increased, the fuel injection amount (hereinafter, “ The amount of in-cylinder combustion fuel can be increased. As the in-cylinder combustion fuel amount increases, the exhaust gas temperature increases, so the temperature of the NOx catalyst 26 can be increased.

  In order to efficiently reduce and purify the NOx stored in the NOx catalyst 26 and release it, the temperature of the NOx catalyst 26 falls within a certain range (hereinafter referred to as “high purification rate temperature range”) as described above. It is important that In other words, when the rich spike control at the time of deceleration is executed, the temperature of the NOx catalyst 26 is not preferable if it is too high exceeding the high purification rate temperature range, and is not preferable if it is too low below the high purification rate temperature range. .

  During an operation state with a low exhaust temperature such as an idle operation state or a light load operation state, the temperature of the NOx catalyst 26 tends to be low. When the rich spike control at the time of deceleration is performed in such a state that the temperature of the NOx catalyst 26 is lowered in this way, the exhaust temperature is raised in order to surely raise the temperature of the NOx catalyst 26 within the high purification rate temperature range. It is preferable.

  On the other hand, the temperature of the NOx catalyst 26 tends to be high during a high load operation state with a high exhaust temperature. Thus, when the rich spike control during deceleration is performed when the NOx catalyst 26 is in a high temperature state, it is not necessary to raise the exhaust temperature so much, rather, the temperature of the NOx catalyst 26 is in the high purification rate temperature range. It is preferable to set an appropriate exhaust temperature so as not to exceed.

  Therefore, in the present embodiment, when the rich spike control during deceleration is executed, the advance angle of the exhaust valve 56 and the in-cylinder combustion fuel amount are changed according to the bed temperature of the NOx catalyst 26.

[Specific Processing in Second Embodiment]
FIG. 5 is a diagram showing the relationship between the bed temperature of the NOx catalyst 26 and the advance angle of the exhaust valve 56 when the rich spike control at the time of deceleration according to the present embodiment is executed. In the present embodiment, it is assumed that the relationship shown in FIG. 5 is stored in the ECU 50 as a map. When executing the process of step 104 of the routine shown in FIG. 4, the advance angle of the exhaust valve 56 according to the bed temperature of the NOx catalyst 26 detected by the catalyst temperature sensor 68 by referring to the map. Is determined, and the exhaust variable valve mechanism 58 is controlled so as to be the advance angle.

  FIG. 6 is a diagram showing the relationship between the bed temperature of the NOx catalyst 26 and the in-cylinder combustion fuel amount when the rich spike control at the time of deceleration according to the present embodiment is executed. In the present embodiment, it is assumed that the relationship shown in FIG. 6 is stored in the ECU 50 as a map. When executing the processing of step 106 of the routine shown in FIG. 4, the in-cylinder combustion fuel amount corresponding to the bed temperature of the NOx catalyst 26 detected by the catalyst temperature sensor 68 is determined by referring to the map. It is determined that the in-cylinder combustion fuel amount is injected from the injector 12 in step 106.

  According to the processing described above, the exhaust temperature can be increased by increasing the in-cylinder combustion fuel amount as the bed temperature of the NOx catalyst 26 is lower during execution of the rich spike control during deceleration. For this reason, even when the NOx catalyst 26 is cold, the temperature of the NOx catalyst 26 can be reliably increased to the high purification rate temperature range, so that the rich spike can be performed with higher efficiency. Further, when the rich spike control at the time of deceleration is executed, if the bed temperature of the NOx catalyst 26 is high, the exhaust gas temperature can be suppressed by reducing the amount of in-cylinder combustion fuel. For this reason, when the temperature of the NOx catalyst 26 is high, the temperature of the NOx catalyst 26 can be reliably controlled so as not to exceed the high purification rate temperature range. For this reason, rich spike can be performed with high efficiency.

  In the maps shown in FIGS. 5 and 6, the exhaust valve advance angle and the in-cylinder combustion fuel amount are linearly changed over the entire region in accordance with the bed temperature of the NOx catalyst 26. It is not limited. For example, when the bed temperature of the NOx catalyst 26 is within a certain range, the exhaust valve advance angle and the in-cylinder combustion fuel amount are made constant, and the exhaust valve advance angle and the in-cylinder combustion fuel amount are changed only before and after the temperature range. May be. Further, the exhaust valve advance angle and the in-cylinder combustion fuel amount may be changed stepwise according to the bed temperature of the NOx catalyst 26.

  In Embodiment 2 described above, the bed temperature of the NOx catalyst 26 is detected by the catalyst temperature sensor 68, but the bed temperature of the NOx catalyst 26 is estimated based on the operating conditions of the diesel engine 10. It may be.

  Further, the bed temperature of the NOx catalyst 26 has a correlation with the temperature of other parts of the exhaust system (for example, the temperature of the exhaust manifold 20, the turbocharger 24, etc.). Therefore, in this embodiment, the temperature of the other part of the exhaust system may be detected or estimated, and the exhaust valve advance angle and the in-cylinder combustion fuel amount may be changed according to the temperature.

  In the second embodiment described above, the catalyst temperature sensor 68 corresponds to the “exhaust system temperature acquisition means” in the fourth invention. Further, the ECU 50 executes the process of step 104 with reference to the map of FIG. 5 so that the “exhaust valve advance means” in the fourth aspect of the invention is the step 106 and the map of FIG. By executing the process 108, the “injection distribution determining means” in the fourth aspect of the present invention is realized.

Embodiment 3 FIG.
Next, the third embodiment of the present invention will be described with reference to FIG. 7. The description will focus on the differences from the first and second embodiments described above, and the description of the same matters will be simplified. Or omitted. The present embodiment can be realized using the same hardware configuration as that of the first embodiment.

[Features of Embodiment 3]
Generally, in the diesel engine 10, the exhaust gas temperature can be increased as the fuel injection timing is delayed. For this reason, even when the rich spike control at the time of deceleration is executed, the exhaust temperature can be raised as the injection timing of the fuel injected in step 106 (hereinafter referred to as “in-cylinder combustion fuel”) is delayed.

  Therefore, in the present embodiment, as in the second embodiment, in order to ensure that the temperature of the NOx catalyst 26 during execution of the deceleration rich spike control more surely falls within the high purification rate temperature range, The injection timing of the in-cylinder combustion fuel is changed according to the temperature. In the present embodiment, when the in-cylinder combustion fuel is injected in a plurality of times, the in-cylinder combustion fuel injection timing is the injection timing of the main injection.

[Specific Processing in Embodiment 3]
FIG. 7 is a diagram showing a relationship between the bed temperature of the NOx catalyst 26 and the injection timing of the in-cylinder combustion fuel when the rich spike control at the time of deceleration according to the present embodiment is executed. In the present embodiment, it is assumed that the relationship shown in FIG. 7 is stored in the ECU 50 as a map. Then, when the processing of step 106 of the routine shown in FIG. 4 is executed, the in-cylinder combustion fuel injection according to the bed temperature of the NOx catalyst 26 detected by the catalyst temperature sensor 68 is referred to by referring to the map. The timing is determined, and in-cylinder combustion fuel is injected from the injector 12 at the injection timing.

According to the map shown in FIG. 7, if the bed temperature of the NOx catalyst 26 is higher than the first predetermined temperature T ₁ of the higher the bed temperature of the NOx catalyst 26, the injection timing is early (to the advance side) Is set. Further, when the bed temperature of the NOx catalyst 26 is lower than the second predetermined temperature T ₂ , the injection timing is set to a later timing (to the retard side) as the bed temperature of the NOx catalyst 26 is lower. The bed temperature of the NOx catalyst 26 when in between the second predetermined temperature T ₂ and the first predetermined temperature T ₁ of the injection timing is kept constant.

  According to the processing described above, when the rich spike control at the time of deceleration is performed, the exhaust temperature can be raised by retarding (delaying) the injection timing of the in-cylinder combustion fuel as the bed temperature of the NOx catalyst 26 is lower. it can. For this reason, even when the NOx catalyst 26 is cold, the temperature of the NOx catalyst 26 can be reliably increased to the high purification rate temperature range, so that the rich spike can be performed with higher efficiency. In particular, during the rich spike control at the time of deceleration according to the present invention, the closing timing of the exhaust valve 52 is advanced in step 104, so that the internal EGR is increased. In the internal EGR, high-temperature burned gas recirculates as it is into the cylinder. For this reason, the more the internal EGR, the higher the in-cylinder temperature. The higher the in-cylinder temperature, the more difficult it is to misfire even when the injection timing is retarded, so the retard limit becomes later. For this reason, when the closing timing of the exhaust valve 52 is advanced, the injection timing can be retarded to a later timing as compared with the normal valve timing. That is, the exhaust temperature can be raised to a higher temperature. Therefore, according to the method of this embodiment, even when the NOx catalyst 26 is cold, the temperature can be quickly and surely increased to the high purification rate temperature range, which is extremely effective.

  Further, according to the present embodiment, when the rich spike control at the time of deceleration is executed, if the bed temperature of the NOx catalyst 26 is high, the exhaust temperature is suppressed by making the in-cylinder combustion fuel injection timing relatively early. Can do. For this reason, when the temperature of the NOx catalyst 26 is high, the temperature of the NOx catalyst 26 can be reliably controlled so as not to exceed the high purification rate temperature range. For this reason, rich spike can be performed with high efficiency.

In the map shown in FIG. 7, but is constant injection timing if the bed temperature of the NOx catalyst 26 is between the second predetermined temperature T ₂ and the first predetermined temperature T _1, the injection timing NOx catalyst It may be made to change linearly over the whole area according to the floor temperature of 26. Further, the injection timing may be changed stepwise according to the bed temperature of the NOx catalyst 26.

  Further, similarly to the above-described second embodiment, the bed temperature of the NOx catalyst 26 may be estimated based on the operating conditions of the diesel engine 10, and further, depending on the temperature of other parts of the exhaust system. Thus, the injection timing of the in-cylinder combustion fuel may be changed.

  In the third embodiment described above, the catalyst temperature sensor 68 corresponds to the “exhaust system temperature acquisition means” in the fifth aspect of the invention. Further, the “injection timing delay means” in the fifth aspect of the present invention is realized by the ECU 50 executing a process of determining the injection timing with reference to the map of FIG.

  In each of the embodiments described above, the rich spike control during deceleration is always performed when the rich spike is performed when the diesel engine 10 is decelerated. However, the deceleration is performed when a specific condition is satisfied. You may make it perform time rich spike control. For example, the rich spike control during deceleration may be performed when the temperature of the exhaust system such as the NOx catalyst 26 is equal to or lower than a predetermined value, and the rich spike may be performed with a fuel cut when the temperature exceeds the predetermined value. .

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the cross section of one cylinder of the diesel engine in the system shown in FIG. It is a figure which shows an example of the valve lift of an intake valve and an exhaust valve in the diesel engine shown in FIG. 1 and FIG. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the relationship between the bed temperature of the NOx catalyst at the time of execution of the rich spike control at the time of deceleration of Embodiment 2 of this invention, and the advance angle of an exhaust valve. It is a figure which shows the relationship between the bed temperature of the NOx catalyst at the time of execution of the rich spike control at the time of deceleration of Embodiment 2 of this invention, and the amount of in-cylinder combustion fuel. It is a figure which shows the relationship between the bed temperature of the NOx catalyst at the time of execution of the rich spike control at the time of deceleration of Embodiment 3 of this invention, and the injection timing of in-cylinder combustion fuel.

Explanation of symbols

10 diesel engine 12 injector 14 common rail 18 exhaust passage 20 exhaust manifold 22 exhaust port 24 turbocharger 26 NOx catalyst 28 intake passage 34 intake manifold 36 intake throttle valve 38 air flow meter 40 external EGR passage 44 EGR valve 46 intake pressure sensor 50 ECU
52 Intake valve 56 Exhaust valve 58 Exhaust variable valve mechanism 62 Crank angle sensor 64 Piston 66 Fuel addition valve 68 Catalyst temperature sensor

Claims (7)

It is provided in the exhaust passage of a diesel engine and has a function of storing NOx in an atmosphere where the air-fuel ratio is greater than the stoichiometric air-fuel ratio, and reducing and purifying the stored NOx in an atmosphere where the air-fuel ratio is less than the stoichiometric air-fuel ratio. NOx catalyst,
A variable valve mechanism that makes at least the closing timing of the exhaust valve of the diesel engine variable;
When decelerating the diesel engine, when decelerating rich spike request determining means for determining whether or not to perform decelerating rich spike control that temporarily sets the air-fuel ratio of the exhaust gas flowing into the NOx catalyst to be equal to or lower than the stoichiometric air-fuel ratio;
First fuel injection means capable of injecting fuel into the working gas so as to burn in the cylinder of the diesel engine;
Second fuel injection means capable of injecting fuel into the working gas so as not to burn in the cylinder of the diesel engine;
Both injections when the first and second fuel injection means inject the required fuel injection amount necessary for setting the exhaust air-fuel ratio to the target air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio when executing the rich spike control during deceleration Injection distribution determining means for determining the distribution of the quantity;
When the deceleration rich spike control is performed, the exhaust valve closes before top dead center so that the combustion gas is compressed in the cylinder so that the diesel engine can generate a braking force. Exhaust valve advance means for controlling the variable valve mechanism to advance the exhaust valve closing timing;
An exhaust emission control device for a diesel engine, comprising:   The injection distribution determining unit determines a fuel injection amount of the first fuel injection unit when the rich spike control at the time of deceleration is performed as a fuel injection amount that provides a predetermined feeling of deceleration, and the requested fuel injection amount 2. The exhaust gas purification apparatus for a diesel engine according to claim 1, wherein a portion not enough is distributed to the second fuel injection means.   The injection distribution determining unit increases the distribution of the fuel injection amount to the first fuel injection unit as the advancement degree of the exhaust valve closing timing at the time of execution of the deceleration rich spike control is larger. The exhaust emission control device for a diesel engine according to claim 1 or 2. An exhaust system temperature acquisition means for detecting or estimating the exhaust system temperature;
The exhaust valve advance means increases the advance angle of the exhaust valve closing timing at the time of execution of the deceleration rich spike control as the exhaust system temperature is lower,
The diesel engine according to any one of claims 1 to 3, wherein the injection distribution determining unit increases the distribution of the fuel injection amount to the first fuel injection unit as the exhaust system temperature is lower. Exhaust purification equipment. Exhaust system temperature acquisition means for detecting or estimating the exhaust system temperature;
Injection timing delay means for delaying the injection timing of the first fuel injection means at the time of execution of the deceleration rich spike control as the exhaust system temperature is lower;
The exhaust purification device for a diesel engine according to any one of claims 1 to 4, further comprising: The variable valve mechanism is one that makes the opening timing of the exhaust valve variable,
6. The diesel engine according to claim 1, wherein the exhaust valve advance means advances the exhaust valve opening timing as well as the exhaust valve closing timing when the deceleration rich spike control is executed. Engine exhaust purification system. An intake throttle valve disposed in the intake passage of the diesel engine;
A deceleration air amount reduction means for reducing the intake air amount by reducing the opening of the intake throttle valve as compared with the non-deceleration when executing the rich spike control during deceleration;
The exhaust purification device for a diesel engine according to any one of claims 1 to 6, further comprising:

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