JP5379733B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust gas purification apparatus that purifies NOx in exhaust gas by disposing a NOx storage reduction catalyst in an exhaust passage.

  In general, in an exhaust gas aftertreatment system for an engine, a NOx occlusion reduction type catalyst is known as a catalyst for nitrogen oxides (NOx). This NOx occlusion reduction type catalyst needs to supply rich gas (HC, CO) serving as a NOx reducing agent to perform NOx regeneration / reduction before NOx is occluded in the catalyst and becomes saturated.

  Conventionally, as a technique for regenerating the NOx occlusion reduction type catalyst, as disclosed in Patent Document 1, a technique for supplying combustion gas at a rich air-fuel ratio as a reducing agent, fuel injection into an exhaust pipe, or the like is used. A technique using unburned gas as a reducing agent is known.

Japanese Patent Laid-Open No. 7-166851

  However, in the technology for enriching the air-fuel ratio during catalyst regeneration, particles such as soot, carbon soot, soluble organic components (SOF), sulfate (SO4), etc., are used due to excess fuel during combustion. Particulate Matter (PM) is generated. In the technology for supplying fuel to the exhaust system, unburned gas on the exhaust side reacts with oxygen blown through the cylinder in the intake stroke, and the temperature of the exhaust system rises excessively, which may damage the catalyst. Not only does it cause generation of particulate matter.

  The present invention has been made in view of the above circumstances, and can supply unburned gas necessary for regeneration of the NOx storage reduction catalyst to improve regeneration efficiency and prevent generation of particulate matter. An object of the present invention is to provide an exhaust purification device.

  In order to achieve the above object, an exhaust emission control device for an engine according to the present invention occludes NOx in exhaust gas in an exhaust passage of the engine in an oxygen-excess atmosphere, and the oxygen concentration in the exhaust gas decreases due to occluded NOx. In an exhaust purification device for an engine having a NOx occlusion reduction type catalyst that is sometimes released, a specific cylinder exhaust that circulates exhaust gas from a specific cylinder to another cylinder by communicating the exhaust side of the specific cylinder and the suction side of another cylinder It has been determined that the gas recirculation passage, the regeneration control execution determination unit for determining whether to execute the regeneration control for reducing and purifying NOx stored in the NOx storage reduction catalyst, and performing the regeneration control are determined. A specific cylinder ignition cut unit that cuts off the ignition of the specific cylinder, and when it is determined that the regeneration control is executed, the control valve interposed in the specific cylinder exhaust gas circulation passage is opened. A specific cylinder exhaust recirculation control unit that reduces the oxygen concentration of the exhaust gas supplied to the NOx occlusion reduction type catalyst by circulating the exhaust gas from the specific cylinder whose ignition is cut to the other cylinder. It is characterized by that.

  The engine exhaust gas purification apparatus according to the present invention stores NOx in the exhaust gas in the exhaust passage of the engine in an excess oxygen atmosphere, and releases the stored NOx when the oxygen concentration in the exhaust gas decreases. In the exhaust emission control device for an engine having an occlusion reduction type catalyst, a regeneration control execution determination unit for judging whether or not to execute regeneration control for reducing and purifying NOx occluded by the NOx occlusion reduction type catalyst, and the above When the regeneration control is determined to be performed, the specific cylinder ignition cut unit that cuts off the ignition of the specific cylinder, and when the regeneration control is determined to be performed, the valve timing of the specific cylinder that has cut the ignition is changed to A specific cylinder exhaust recirculation that reduces the oxygen concentration of the exhaust gas supplied to the NOx occlusion reduction type catalyst by increasing the exhaust gas internal ring flow rate of the specific cylinder Characterized by comprising a control unit.

  According to the present invention, it is possible to supply only the unburned gas necessary for regeneration of the NOx occlusion reduction catalyst to improve the regeneration efficiency and prevent the generation of particulate matter.

1 is a configuration diagram of an engine control system according to a first embodiment of the present invention. Same as above, functional block diagram related to LNT playback control Same as above, flowchart of LNT regeneration control routine Explanatory drawing which shows typically internal EGR by the change of valve timing concerning 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
First, a first embodiment of the present invention will be described. In FIG. 1, reference numeral 1 denotes an engine. In the present embodiment, as shown in the figure, the engine has # 1 to # 4 cylinders, and the cylinder head 2 supplies fuel to the intake port of each cylinder or to the cylinder. This is a spark ignition gasoline engine (hereinafter simply referred to as “engine”) provided with an injector 50 for injection and a spark plug 51 for spark discharge to burn the air-fuel mixture in the cylinder.

  The configuration of the intake side of the engine 1 is that an intake manifold 3 having a branch portion communicating with an intake port of each cylinder is connected to the cylinder head 2, and a throttle is provided in an intake passage 4 where the branches of the intake manifold 3 gather. A valve 5 is interposed. The throttle valve 5 is connected to an actuator 6 that controls the throttle opening by a control signal from an engine control unit (ECU) 100.

  Further, an intercooler 7 is interposed upstream of the throttle valve 5, a compressor 8a of the turbocharger 8 is interposed upstream of the intercooler 7, and an air cleaner 9 is interposed upstream of the compressor 8a. Has been. An intake air amount sensor 10 is interposed downstream of the air cleaner 9.

  On the other hand, as a configuration on the exhaust side of the engine 1, an exhaust manifold 11 having a branch portion communicating with an exhaust port of each cylinder is connected to the cylinder head 2, and an exhaust passage 12 where the branches of the exhaust manifold 11 are gathered is provided. A turbine 8b of the turbocharger 8 is interposed. The turbocharger 8 is, for example, a well-known variable nozzle turbocharger (VGT). A vane of a variable nozzle provided around the turbine 8b is opened by a control signal from the ECU 100. An actuator 13 for controlling the degree is connected via a link mechanism (not shown).

  The exhaust passage 12 on the upstream side of the turbine 8 b is bypass-connected to the intake passage 4 on the downstream side of the throttle valve 5 via an exhaust gas recirculation (EGR) passage 14. The EGR passage 14 is provided with an EGR cooler 15 that cools EGR gas and an EGR control valve 16 that controls the amount of EGR from the EGR passage 14 by a control signal from the ECU 100.

  Further, the EGR passage 14 is used as a first EGR passage, and in addition to the first EGR passage, a branch of a specific cylinder (# 4 cylinder in the present embodiment) of the exhaust manifold 11 and other parts of the intake manifold 3 A second EGR passage 17 is provided to communicate with the branch of the cylinder (# 1 cylinder in the present embodiment). The second EGR passage 17 forms a specific cylinder exhaust gas recirculation passage that directly connects the exhaust side of the specific cylinder and the suction side of the other cylinder to circulate exhaust gas from the specific cylinder to the other cylinder. The second EGR passage 17 is provided with an EGR control valve 18 that controls an EGR amount to be recirculated from a specific cylinder to another cylinder by a control signal from the ECU 100.

  Further, a catalytic converter 20 for purifying the exhaust gas that has passed through the turbine 8b is interposed in the exhaust passage 12 on the downstream side of the turbine 8b. An O2 sensor 21 that detects the oxygen concentration in the exhaust gas is exposed on the upstream side of the catalytic converter 20, and a NOx sensor 22 that detects the NOx concentration in the exhaust gas is exposed on the downstream side of the catalytic converter 20. Has been.

  In the catalytic converter 20, NOx generated by the reaction of oxidation of HC (hydrocarbon) and CO (carbon monoxide), which are incomplete combustion components in the exhaust gas, and nitrogen in the air and unburned oxygen. The three-way catalyst 20a that simultaneously promotes the reduction of (nitrogen oxide) and NOx in the air-fuel ratio lean region (under an oxygen-excess atmosphere) that cannot be purified by the three-way catalyst 20a are collected, stored, and reduced and purified. A NOx occlusion reduction type catalyst (Lean NOx Trap catalyst; LNT) 20b is accommodated in order from the upstream side.

  The LNT 20b, for example, has a NOx occlusion material such as alkali metals, alkaline earths, and rare earths and a noble metal such as platinum supported on a support such as alumina, and the oxygen concentration of the exhaust gas is reduced by the storage function of NOx and O2. When it is high, HC and CO are oxidized and reduced and NOx is occluded. When the oxygen concentration in the exhaust gas decreases, the stored NOx is released, and NOx is reduced and purified by HC and CO that are left without being oxidized and reduced.

Next, an electronic control system centering on the ECU 100 will be described.
The ECU 100 is an electronic control device that includes a microcomputer including a CPU, ROM, RAM, I / O interface, and the like, and includes an A / D converter, a timer, a counter, various logic circuits, various drive circuits, and the like. ing. The ECU 100 includes various types (not shown) such as the intake air amount sensor 10, the O2 sensor 21, the NOx sensor 22, the crank angle sensor that detects the rotational position of the crankshaft, and the accelerator pedal sensor that detects the depression amount of the accelerator pedal. Sensors and switches are connected via an input interface, an injector 50, an ignition coil that induces a high voltage for generating spark discharge in the spark plug 51, an actuator 6 that drives the throttle valve 5 to open and close, a turbocharger Various actuators such as the actuator 13 of the machine 8 and the EGR control valves 16 and 18 are connected via an output interface.

  The ECU 100 is connected to an in-vehicle network (not shown) based on a communication protocol such as CAN (Controller Area Network), and is connected to an in-vehicle network such as a transmission ECU for controlling a transmission and a brake ECU for controlling a brake. In addition to receiving various control information from the other ECU via the in-vehicle network, the control information to the other ECU is sent to the in-vehicle network.

  The ECU 100 drives various actuators based on signals from the various sensors and switches described above and various control information input via the in-vehicle network, and performs fuel injection control, ignition timing control, supercharging pressure control, EGR. Various engine controls such as control are executed. In this engine control, during normal operation, the air amount and fuel injection amount that achieve the target air-fuel ratio based on the engine speed based on the signal from the crank angle sensor and the accelerator opening based on the signal from the accelerator pedal sensor. The engine combustion state is optimally controlled. In the present embodiment, the control to the target air-fuel ratio is based on feedback control to the stoichiometric air-fuel ratio based on the signal from the O2 sensor 21.

  Further, the ECU 100 periodically monitors the NOx occlusion state of the LNT 20b, and when the NOx occlusion amount of the LNT 20b reaches a predetermined maximum amount, the NOx occluded in the LNT 20b is released and reduced and purified. Execute control. In this LNT regeneration control, the air-fuel ratio is intentionally enriched and the unburned gas is not supplied to the LNT 20b as in the prior art. Instead, the control state to the stoichiometric air-fuel ratio is maintained, and then the ignition of a specific cylinder is performed. To cut. Then, the exhaust gas from the specific cylinder subjected to the ignition cut is recirculated to another ignition cylinder via the second EGR passage 17, thereby reducing the oxygen concentration of the exhaust gas supplied to the LNT 20b and releasing / reducing NOx. Promote.

  Therefore, the ECU 100 includes a regeneration control execution determination unit 101, a specific cylinder ignition cut unit 102, and a specific cylinder exhaust recirculation control unit 103 as main functions related to the regeneration control of the LNT 20b, as shown in FIG. With this functional configuration, when the regeneration control execution determination unit 101 determines that regeneration of the LNT 20b is necessary, the normal control shifts to LNT regeneration control, and the specific cylinder ignition cut unit 102 and the specific cylinder exhaust recirculation control unit 103 perform the control of the LNT 20b. Performs playback processing.

  Specifically, the regeneration control execution determination unit 101 estimates the NOx occlusion amount of the LNT 20b based on the engine operating state and a signal from the NOx sensor 22, and when the NOx occlusion amount reaches a preset maximum amount, The execution determination of the LNT reproduction control is performed on the assumption that the reproduction process is necessary. In order to execute the LNT regeneration control, the conditions under which the LNT 20b is in an active state, the conditions under which feedback control to the stoichiometric air-fuel ratio is not performed during acceleration operation, the conditions under which the exhaust gas temperature is equal to or higher than a predetermined temperature, It is desirable that the operation condition is such that normal EGR through the EGR passage 14 is not performed. If the operation condition is not satisfied, the LNT regeneration control is executed after the condition is satisfied.

  For example, when estimating the NOx occlusion amount from the engine operating state, the NOx emission amount of the engine per unit time is obtained in advance through experiments or simulations using the engine speed and the engine load (accelerator opening) as parameters, In the ECU 100, the map is stored and the like, and the maximum value of the NOx occlusion amount of the LNT 20b set in advance in consideration of the capacity and characteristics of the LNT 20b is stored as a collection limit value. Then, the NOx emission amount obtained by referring to the map based on the engine speed and the accelerator opening is integrated at regular intervals, and when this integrated value reaches the NOx collection limit value held in advance, regeneration control of the LNT 20b is necessary. It is determined that

  In addition, when estimating the NOx occlusion amount of the LNT 20b based on the signal from the NOx sensor 22, the characteristic (saturation characteristic) of NOx concentration change over time until the NOx occlusion amount of the LNT 20b reaches saturation is stored in the ECU 100 in advance. The change in the NOx concentration in the exhaust gas downstream of the LNT 20b is monitored by a signal from the NOx sensor 22 in advance. When the change in the NOx concentration with respect to the time after the end of the previous LNT regeneration control reaches the threshold value set from the saturation characteristics, it is determined that the regeneration control of the LNT 20b is necessary.

  The determination result of the LNT regeneration control by the regeneration control execution determination unit 101 is sent to the specific cylinder ignition cut unit 102 and the specific cylinder exhaust recirculation control unit 103, and is instructed to perform the ignition cut of the specific cylinder and the EGR execution of the specific cylinder, respectively. . That is, the specific cylinder ignition cut unit 102 receives the execution determination of the LNT regeneration control, and cuts the ignition of a specific cylinder among the cylinders that are feedback controlled to the theoretical air-fuel ratio. Further, the specific cylinder exhaust recirculation control unit 103 receives the execution determination of the LNT regeneration control, opens the EGR control valve 18 of the second EGR passage 17, and removes the unburned gas discharged from the specific cylinder whose ignition has been cut. Recirculate to other combustion cylinders.

  In the present embodiment, the ignition of the # 4 cylinder is cut, and the exhaust gas from the # 4 cylinder that has been cut off is recirculated to the # 1 cylinder via the second EGR passage 17. Then, the unburned gas recirculated to the # 1 cylinder is mixed in the exhaust gas from the combustion cylinder to reduce the oxygen concentration of the exhaust gas sent to the LNT 20b, and the stored NOx is released and regenerated by reduction.

  The processing of each functional unit of the ECU 100 related to the above LNT regeneration control is realized by the program processing shown in the flowchart of FIG. Next, program processing relating to LNT regeneration control by ECU 100 will be described using a flowchart of an LNT regeneration control routine shown in FIG.

  This LNT regeneration control routine is a routine that is executed at regular intervals during normal operation. First, based on the NOx concentration in the exhaust gas detected by the NOx sensor 22 in the first step S1, the NOx of the LNT 20b. It is examined whether or not the collected amount (NOx occlusion amount) has reached the limit. As a result, when the amount of NOx trapped by the LNT 20b has not reached the limit, the routine is directly exited and normal operation is continued. On the other hand, when the amount of NOx collected by the LNT 20b has reached the limit, the process proceeds from step S1 to step S2 to execute LNT regeneration control.

  In this LNT regeneration control, the ignition of the # 4 cylinder is cut while performing feedback control to the theoretical air-fuel ratio based on the signal of the O2 sensor 21. Then, the unburned gas discharged from the # 4 cylinder is introduced into the cylinder of the # 1 cylinder by the external EGR via the second EGR passage 17 as a reducing agent used for regeneration of the LNT 20b. The unburned gas sent to the LNT 20b by the external EGR is controlled to an amount necessary for regeneration of the LNT 20b by controlling the opening degree of the EGR control valve 18 or the fuel injection amount to the ignition cut cylinder.

  Thereafter, the process proceeds to step S3, where the NOx occlusion state of the LNT 20b is checked again, and compared with the regeneration end threshold value to determine whether or not to end the LNT regeneration control. When the NOx occlusion amount exceeds the regeneration end threshold value, it is determined that the LNT regeneration control has not ended, and the process of step S2 is continued. When the NOx occlusion amount falls below the regeneration end threshold value, When it is determined that the LNT regeneration control has been completed, the routine returns to normal operation in step S4, and this routine is exited.

  As described above, in the present embodiment, the ignition of some specific cylinders is cut under the control state to the stoichiometric air-fuel ratio, and the cylinders of other combustion cylinders are discharged from the specific unburned cylinders that have been ignited by external EGR. Introduce gas excluding oxygen. As a result, it is possible to supply an amount of unburned gas (reduced component) necessary for regeneration of LNT, and to reduce excess fuel at the time of combustion compared to regeneration processing using a rich air-fuel ratio as in the past. Thus, an efficient reduction reaction can be realized and generation of PM can be suppressed. Further, unlike the technique of injecting fuel into the exhaust system as a reducing agent for LNT regeneration, there is no possibility that the exhaust system becomes hot and damages the catalyst.

  Next, a second embodiment of the present invention will be described. In the second mode, the valve timing of a specific cylinder to be ignited is changed to increase the internal EGR, thereby lowering the oxygen concentration of the exhaust gas and performing LNT regeneration control.

  In the first embodiment, the engine does not necessarily have a variable valve timing mechanism, and can be applied to any engine of intake pipe fuel injection and in-cylinder fuel injection. In the second embodiment, variable valve timing is used. The engine is provided with a mechanism and injects fuel directly into a cylinder. Further, the second EGR passage 17 for performing external EGR from the specific cylinder to be cut off to another combustion cylinder is not particularly required.

  Accordingly, the function of the specific cylinder exhaust recirculation control unit 103 is slightly changed as a partial function of the ECU 100. When it is determined that the LNT regeneration control is to be executed, the specific cylinder exhaust gas recirculation control unit 103 according to the second embodiment changes the valve timing of the specific cylinder whose ignition has been cut through the variable valve timing mechanism, and the internal EGR amount of the specific cylinder Increase.

  As shown in FIG. 4A, the valve timing is changed by increasing the valve overlap between the intake valve 1a and the exhaust valve 1b via the variable valve timing mechanism 60 in the first half of the intake stroke of the ignition cut cylinder. By expanding the valve overlap in the intake stroke, the low temperature fresh air (oxygen) once flowing into the cylinder is blown back to the intake side by the internal EGR, and the high temperature gas is introduced into the combustion chamber 1c. Then, it is mixed with the fuel injected into the combustion chamber 1c in the latter half of the intake stroke or the first half of the compression stroke, and as shown in FIG. 4B, unburned gas having a low oxygen concentration is discharged in the exhaust stroke, and the reducing agent is supplied to the LNT 20b. The LNT 20b is reproduced.

  The variable valve timing mechanism may be provided in one cylinder as a specific cylinder. However, in an engine having a variable valve timing mechanism for each cylinder group (bank) such as a horizontally opposed engine and a V-type engine, The valve timing may be changed with the cylinder group of the bank as a specific cylinder. The variable valve timing mechanism uses a mechanism that varies the relative phase between the intake cam and the exhaust cam by a known hydraulic drive type or electromagnetic drive type mechanism. Although FIG. 4 shows an example in which the variable valve timing mechanism is provided only on the exhaust side, it may be provided only on the intake side or on both the intake side and the exhaust side.

  In the second embodiment, as in the first embodiment, an unburned gas (reducing component) in an amount necessary for the regeneration of LNT can be supplied, and excess fuel is reduced to realize an efficient reduction reaction. Generation | occurrence | production of PM can be suppressed.

DESCRIPTION OF SYMBOLS 1 Engine 17 2nd EGR channel | path 18 EGR control valve 20b NOx occlusion reduction type | mold catalyst 60 Variable valve timing mechanism 100 Engine control apparatus 101 Reproduction | regeneration control execution determination part 102 Specific cylinder ignition cut-off part 103 Specific cylinder exhaust recirculation control part

Claims (4)

In an engine exhaust gas purification apparatus having a NOx occlusion reduction type catalyst that stores NOx in exhaust gas in an exhaust passage of the engine in an oxygen excess atmosphere and releases the stored NOx when the oxygen concentration in the exhaust gas decreases. ,
A specific cylinder exhaust gas recirculation passage for communicating exhaust gas from a specific cylinder to another cylinder by communicating the exhaust side of the specific cylinder and the suction side of another cylinder;
A regeneration control execution determining unit that determines whether to perform regeneration control for releasing and reducing NOx stored in the NOx storage reduction catalyst;
A specific cylinder ignition cut unit that cuts off the ignition of the specific cylinder when it is determined to execute the regeneration control;
When it is determined that the regeneration control is performed, the control valve interposed in the specific cylinder exhaust gas recirculation passage is opened to circulate exhaust gas from the specific cylinder that cuts off the ignition to the other cylinder, An engine exhaust gas purification apparatus comprising: a specific cylinder exhaust gas recirculation control unit that reduces an oxygen concentration of exhaust gas supplied to the NOx storage reduction catalyst. In an engine exhaust gas purification apparatus having a NOx occlusion reduction type catalyst that stores NOx in exhaust gas in an exhaust passage of the engine in an oxygen excess atmosphere and releases the stored NOx when the oxygen concentration in the exhaust gas decreases. ,
A regeneration control execution determining unit that determines whether to perform regeneration control for releasing and reducing NOx stored in the NOx storage reduction catalyst;
A specific cylinder ignition cut unit that cuts off ignition of a specific cylinder when it is determined that the regeneration control is performed;
When it is determined that the regeneration control is executed, the exhaust gas supplied to the NOx occlusion reduction type catalyst is increased by changing the valve timing of the specific cylinder whose ignition is cut to increase the exhaust gas internal ring flow rate of the specific cylinder. An exhaust purification device for an engine, comprising: a specific cylinder exhaust recirculation controller that reduces the oxygen concentration of the gas.   The engine exhaust gas purification apparatus according to claim 1 or 2, wherein the ignition cut of the specific cylinder is performed under a control state in which the fuel injection amount and the air amount of each cylinder are controlled to a stoichiometric air-fuel ratio.   3. The engine exhaust purification system according to claim 2, wherein the engine is an in-cylinder fuel injection engine that directly injects fuel into a cylinder.

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