JP2007127020A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for appropriately regenerating NOx occlusion reduction catalyst while suitably reducing NOx by controlling a flow rate of exhaust gas 7 even in various operation states. <P>SOLUTION: An exhaust emission control device which is equipped with NOx occlusion reduction catalysts 10, 12 at some midpoints of exhaust flow passages 11, 13 and which reduces and purifies NOx by adding fuel as a reducing agent to the upstream side of the NOx occlusion reduction catalysts 10, 12, contains fuel addition means 15, 19 which are provided to the exhaust flow passages 11, 13 on the upstream side from the NOx occlusion reduction catalysts 10, 12 and which inject fuel, flow passage regulating valves 16, 20 which are mounted in the exhaust flow passages 11, 13 on the upstream side from the fuel addition means 15, 19 and which regulates openings of the exhaust flow passages 11, 13, and flow rate sensors 17, 21 for detecting the flow rate of exhaust gas 7 to send control signals to the flow passage regulating valves 16, 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

Conventionally, exhaust purification is carried out with an exhaust purification catalyst installed in the middle of the exhaust pipe. As this type of exhaust purification catalyst, NOx in exhaust gas is oxidized when the exhaust air-fuel ratio is lean. Thus, a NOx occlusion reduction catalyst having the property of temporarily storing in the form of nitrate and decomposing and releasing NOx through the intervention of unburned HC, CO, etc. when the O ₂ concentration in the exhaust gas decreases is reduced and purified. is there.

  As this type of NOx occlusion reduction catalyst, platinum / barium / alumina catalyst, platinum / potassium / alumina catalyst, and the like have already been known.

Then, in the NOx storage reduction catalyst, when the storage amount of NOx will reach a saturation amount increases, it becomes impossible occludes more NOx, O ₂ in the exhaust gas flowing into the regular NOx storage reduction catalyst It is necessary to decompose and release NOx by reducing the concentration.

For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the O ₂ concentration in the exhaust gas and unburned HC in the exhaust gas. It is possible to promote the decomposition and release of NOx by increasing reducing components such as CO and CO. However, when the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine, it is difficult to operate the engine at a rich air-fuel ratio. is there.

For this reason, fuel addition means is installed in the exhaust pipe upstream of the NOx storage reduction catalyst, and fuel (HC) is injected and added into the exhaust gas by the fuel addition means, so that this added fuel is used as a reducing agent. The O ₂ concentration in the exhaust gas is lowered by reacting with O ₂ on the NOx storage reduction catalyst. At the same time, a flow path adjustment valve is installed in the exhaust pipe upstream of the fuel addition means, and the flow path adjustment valve opens the exhaust gas flow path in a predetermined time to control the flow rate of the exhaust gas ( For example, see Patent Documents 1 and 2).
JP 2003-247416 A Japanese Patent Laid-Open No. 2004-162600

  However, when the engine operating state changes, the flow rate of the exhaust gas flowing into the NOx storage reduction catalyst changes. Therefore, in the configuration in which the flow rate of the exhaust gas is controlled by the flow path adjustment valve as in the conventional example, There has been a problem that NOx cannot be suitably reduced and the NOx storage reduction catalyst cannot be properly regenerated.

  The present invention has been made in view of the above-described circumstances, and provides an exhaust purification device that controls the flow rate of exhaust gas to reduce NOx appropriately even in various operating conditions and appropriately regenerates and controls the NOx storage reduction catalyst. The purpose is to do.

  The present invention is an exhaust emission control device equipped with a NOx storage reduction catalyst in the middle of an exhaust passage and configured to reduce and purify NOx by adding fuel as a reducing agent upstream of the NOx storage reduction catalyst. A fuel addition means installed in the exhaust passage upstream of the NOx occlusion reduction catalyst and injecting fuel; and an opening of the exhaust passage arranged in the exhaust passage upstream of the fuel addition means is adjusted. The present invention relates to an exhaust gas purification device including a flow path adjustment valve and a flow rate sensor that detects a flow rate of exhaust gas and sends a control signal to the flow path adjustment valve.

  In the present invention, it is preferable that the flow path adjustment valve adjusts the opening degree of the exhaust flow path so that the flow rate of the exhaust gas in the exhaust flow path matches the target exhaust gas flow rate set by the control map of the engine speed. .

  In the present invention, it is preferable that a plurality of exhaust passages equipped with NOx occlusion reduction catalysts are provided in parallel, and the exhaust passages are switched by a passage adjustment valve.

  The present invention preferably includes a λ sensor that is installed in the exhaust passage downstream of the NOx storage reduction catalyst and detects the excess air ratio of the exhaust gas.

The present invention preferably includes an O ₂ sensor that is installed in the exhaust passage downstream of the NOx storage reduction catalyst and detects the O ₂ concentration in the exhaust gas.

  Thus, according to the present invention, the engine includes the flow path adjustment valve that adjusts the opening degree of the exhaust flow path and the flow rate sensor that detects the flow rate of the exhaust gas and sends a control signal to the flow path adjustment valve. Even when the exhaust gas flow rate changes depending on the operation state, the flow rate sensor and the flow path control valve control the exhaust gas flow rate, so that NOx can be suitably reduced and the NOx storage reduction catalyst is appropriately regenerated and controlled. can do.

  The flow path adjustment valve adjusts the exhaust flow path so that the exhaust gas flow rate in the exhaust flow path matches the target exhaust gas flow rate set by the engine speed control map. The target exhaust gas flow rate can be changed, so even when the exhaust gas flow rate changes depending on the engine operating state, the flow rate sensor and the flow path adjustment valve are used to control the exhaust gas flow rate to an appropriate state. The NOx occlusion reduction catalyst can be suitably regenerated and controlled.

  If multiple exhaust passages equipped with NOx storage reduction catalyst are provided in parallel and the exhaust passage is switched by the passage adjustment valve, one exhaust passage is opened by the passage adjustment valve and the NOx storage reduction catalyst is used. At the same time, the other exhaust passage is closed to regenerate the other NOx storage reduction catalyst, so that a plurality of NOx storage reduction catalysts can be controlled alternately to regenerate, and NOx can be suitably reduced and the NOx storage reduction catalyst can be reduced. Appropriate playback control can be performed.

  If a λ sensor is installed in the exhaust passage downstream of the NOx storage reduction catalyst and detects the excess air ratio of the exhaust gas, the excess air ratio in the exhaust gas is detected by the λ sensor, and feedback control is performed. The NOx storage reduction catalyst can be suitably regenerated and controlled by operating the fuel addition means or / and the flow path regulating valve under appropriate conditions.

When provided with the O ₂ sensor that the NOx storage-reduction catalyst is disposed in an exhaust passage on the downstream side detects the O ₂ concentration in the exhaust gas, the O ₂ sensor detected and feedback control of the O ₂ concentration in the exhaust gas Therefore, the NOx occlusion reduction catalyst can be suitably regenerated and controlled by operating the fuel addition means or / and the flow path adjustment valve under appropriate conditions.

  According to the above-described exhaust purification device of the present invention, it is possible to achieve an excellent effect of controlling the exhaust gas flow rate to suitably reduce NOx and appropriately controlling the regeneration of the NOx storage reduction catalyst even in various operating states. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In the figure, reference numeral 1 denotes a diesel engine. In the diesel engine 1 shown here, a turbocharger 2 is provided and led from an air cleaner 3. The air 4 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and from the intercooler 6 to an intake manifold (not shown). Air 4 is guided and introduced into each cylinder of the diesel engine 1.

  Further, in each cylinder of the diesel engine 1, liquid fuel (light oil) from a fuel tank (not shown) is injected into each cylinder of the diesel engine 1 and burned, and from each cylinder of the diesel engine 1. The discharged exhaust gas 7 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 that has driven the turbine 2b is discharged downstream through the exhaust pipe 9.

  Downstream of the exhaust pipe 9, a first exhaust passage 11 equipped with one NOx storage reduction catalyst 10 and another NOx storage reduction catalyst 12 are installed so that two passages are arranged in parallel by branching. The second exhaust flow path 13 is provided, and downstream of the first exhaust flow path 11 and the second exhaust flow path 13 is provided with a downstream exhaust flow path 14 that merges into one. ing.

  In the first exhaust passage 11, a fuel addition nozzle 15 of a first fuel addition means that is installed upstream of the NOx storage reduction catalyst 10 and injects fuel of the reducing agent, and upstream of the fuel addition nozzle 15. A first flow path adjustment valve 16 that is installed in the vicinity of the branch point and adjusts the opening degree of the first exhaust flow path 11, a fuel addition nozzle 15 of the first fuel addition means, and the NOx occlusion reduction catalyst 10. A first flow rate sensor 17 that is installed in between and detects the flow rate of the exhaust gas 7; a first λ sensor 18 that is installed downstream of the NOx storage reduction catalyst 10 and detects the excess air ratio of the exhaust gas 7; An inlet temperature sensor (not shown) disposed downstream of the first flow rate sensor 17 and in front of the NOx storage reduction catalyst, and an outlet disposed upstream of the first λ sensor 18 and behind the NOx storage reduction catalyst. And a temperature sensor (not shown).

  In the second exhaust passage 13, a fuel addition nozzle 19 of a second fuel addition means that is installed upstream of the NOx storage reduction catalyst 12 and injects fuel of the reducing agent, and upstream of the fuel addition nozzle 19. A second flow path adjustment valve 20 that is installed in the vicinity of the branch point and adjusts the opening degree of the second exhaust flow path 13, a fuel addition nozzle 19 of the second fuel addition means, and the NOx occlusion reduction catalyst 12. A second flow rate sensor 21 installed between them to detect the flow rate of the exhaust gas 7, and a second λ sensor 22 installed downstream from the NOx storage reduction catalyst 12 to detect the excess air ratio of the exhaust gas 7; An inlet temperature sensor (not shown) disposed downstream of the second flow rate sensor 21 and in front of the NOx storage reduction catalyst, and an outlet disposed upstream of the second λ sensor 22 and behind the NOx storage reduction catalyst. And a temperature sensor (not shown).

Here, the NOx occlusion reduction catalysts 10 and 12 are not particularly limited, but Pt noble metals, Li, Na, Mg, K, Ca, Cs, Ba, Y, La, Ce, Pr, Nd, and Eu. In addition to lanthanoid-based metal NOx storage agents, alumina, titania, zirconia, and the like. The fuel addition nozzle 15 of the first fuel addition means and the fuel addition nozzle 19 of the second fuel addition means are supplied with a reducing agent fuel such as light oil from a fuel tank 24 through a supply pipe 25 by a pressure pump 23. Is to be supplied. Further, the first exhaust flow path 11 and the second exhaust passage 13, a first λ sensor 18, in place of the second λ sensor 22 may be provided with O ₂ sensor for detecting the O ₂ concentration .

  The downstream exhaust passage 14 has a catalytic particulate filter 26, an inlet temperature sensor (not shown) disposed in front of the particulate filter 26, and an outlet disposed in the rear of the particulate filter 26. And a temperature sensor (not shown).

  Here, the particulate filter 26 is mainly composed of a filter body having a porous honeycomb structure made of ceramic such as cordierite, and the inlets of the respective flow paths partitioned in a lattice shape in the filter body are alternately arranged by plugs. As for the flow path that is sealed by the inlet and the inlet is not sealed, the outlet is sealed by the plug, and only the exhaust gas that has passed through the porous thin wall that defines each flow path is sealed. It is discharged downstream and particulates are collected on the inner surface of the porous thin wall.

On the other hand, the fuel addition nozzle 15 of the first fuel addition means, the fuel addition nozzle 19 of the second fuel addition means, the first flow path adjustment valve 16, and the second flow path adjustment valve 20 are connected to an engine control computer (ECU). Is connected to a control device (control means) 27 also serving as an electronic control unit, and is controlled by a control signal. The control device 27 includes a first flow rate sensor 17, an inlet temperature sensor of the NOx storage reduction catalyst 10, and Outlet temperature sensor, first λ sensor 18 or O ₂ sensor, second flow rate sensor 21, inlet temperature sensor and outlet temperature sensor of NOx storage reduction catalyst 12, second λ sensor 22 or O ₂ sensor, particulate filter Data are inputted from 26 inlet temperature sensors and outlet temperature sensors, and a rotation sensor (not shown) for detecting the engine speed of the diesel engine 1 is also shown. The rotation speed signal (engine rotation speed) is input from), so that the load signal from the accelerator sensor (not shown) for detecting a depression angle of an accelerator pedal (not shown) is input.

Further, in the control device 27, based on the rotational speed signal (engine rotational speed) from the rotation sensor and the fuel injection amount by the first fuel addition means and the second fuel addition means, the control map 27 The target exhaust gas flow rates of the exhaust flow path 11 and the second exhaust flow path 13 are read and determined, and the excess air ratio of the exhaust gas 7 from the first λ sensor 18 and the second λ sensor 22 is determined. Or the O ₂ concentration data from the O ₂ sensor is fed back. Here, the control map of the control device 27 is not limited to the one based on the rotational speed signal (engine rotational speed) and the fuel injection amount, but the rotational speed signal (engine rotational speed) from the rotational sensor, the inlet temperature sensor, and the outlet. It may be based on the temperature of the NOx storage reduction catalysts 10 and 12 from the temperature sensor, and is not particularly limited.

  The operation of the embodiment for carrying out the present invention will be described below.

  When the exhaust gas 7 is discharged from the diesel engine 1, the first exhaust passage 11 or the second exhaust passage is opened and closed by opening and closing the first passage adjustment valve 16 and the second passage adjustment valve 20. The exhaust gas 7 is purified by any one of the NOx storage reduction catalysts 10, 12, and the NOx storage reduction catalysts 12, 10 are regenerated on the other side. In the following example, the first flow path adjustment valve 16 is opened, the exhaust gas 7 is purified by the NOx occlusion reduction catalyst 10 in the first exhaust flow path 11, and the second flow path adjustment valve 20 is closed at the same time. A case where the NOx storage reduction catalyst 12 in the second exhaust flow path 13 is regenerated is shown.

In the first exhaust passage 11, the exhaust gas 7 flows on the NOx storage reduction catalyst 10, and on the NOx storage reduction catalyst 10, NOx and O ₂ in the exhaust gas 7 react to store NOx in the form of nitrate. Then, the exhaust gas 7 is purified.

  In the second exhaust passage 13, the reducing agent fuel is added from the fuel addition nozzle 15 of the second fuel addition means, and the relative excess air ratio with respect to the amount of fuel added is reduced to react the reducing agent with NOx. The selectivity is improved, whereby NOx is actively decomposed and released from the NOx storage reduction catalyst 12 to regenerate the NOx storage reduction catalyst 12, and simultaneously the released NOx reacts with the fuel on the NOx storage reduction catalyst 12. Reduce and purify.

  Here, when the NOx occlusion reduction catalyst 12 is regenerated, the flow rate of the exhaust gas 7 is measured by the second flow rate sensor 21 and the data is sent to the control device 27. 2) and the second flow path adjustment valve 20 is controlled so that the flow rate of the exhaust gas 7 in the second exhaust flow path 13 is matched with the target exhaust gas flow rate set by the control map based on the fuel injection amount. When the flow rate of the exhaust gas 7 is higher than the target exhaust gas flow rate, the opening degree of the second flow path adjustment valve 20 is reduced, and when the flow rate of the exhaust gas 7 is lower than the target exhaust gas flow rate, the second flow rate is adjusted. The opening of the path adjustment valve 20 is opened.

  Further, in a transient operation state in which the operation state (rotation speed, torque) of the diesel engine 1 changes and the flow rate of the exhaust gas 7 changes, the second flow rate adjustment is performed by the second flow sensor 21 detecting at any time. The valve 20 is finely controlled to change the opening degree of the second exhaust passage 13 to an optimum state, corresponding to the change in the flow rate of the exhaust gas 7.

At the same time, the second λ sensor 22 in the second exhaust flow path 13 detects the excess air ratio in the exhaust gas 7 and sends it to the control device 27 to optimize the amount of fuel added by the second fuel addition means. Feedback control is performed. When an O ₂ sensor is used instead of the second λ sensor 22, the O ₂ concentration in the exhaust gas 7 is detected and sent to the control device 27, and the fuel of the second fuel addition means is similarly detected. Feedback control is performed to optimize the addition amount.

  Further, the particulate filter 26 downstream of the first exhaust passage 11 and the second exhaust passage 13 captures soot in the exhaust gas 7 and burns it.

  After the regeneration of the NOx storage reduction catalyst in the second exhaust passage 13 is completed, the first passage adjustment valve 16 is closed and the second passage adjustment valve 20 is opened. The NOx storage reduction catalyst 10 in the exhaust passage 11 is regenerated, and the exhaust gas 7 is purified by the NOx storage reduction catalyst 12 in the second exhaust passage 13.

  Thus, according to the embodiment, the first flow path adjustment valve 16 and the second flow path adjustment valve 20 that adjust the opening degree of the first exhaust flow path 11 and the second exhaust flow path 13 are used. And a first flow rate sensor 17 and a second flow rate sensor 21 that detect the flow rate of the exhaust gas 7 and send control signals to the first flow path adjustment valve 16 and the second flow path adjustment valve 20. Even when the flow rate of the exhaust gas 7 changes due to the transition of the operating state of the engine, the first flow rate sensor 17, the second flow rate sensor 21, the first flow path adjustment valve 16, and the second flow path adjustment The flow rate of the exhaust gas 7 can be controlled by the valve 20 so that NOx can be suitably reduced and the NOx storage reduction catalysts 10 and 12 can be appropriately regenerated and controlled.

  In fact, according to the results of experiments conducted by the present inventors, in the example in which fuel is added in the embodiment in the transient state of the diesel engine 1, as shown in the graph of FIG. While a high NOx reduction rate can be obtained, in the comparative example in which fuel addition is performed in the form without a flow rate sensor as in the conventional case, only a NOx reduction rate of about 33% is obtained, In the embodiment, it is clear that NOx is suitably reduced.

  In the embodiment, the first flow path adjustment valve 16 and the second flow path adjustment valve 20 have the target exhaust gas flow rate set by the engine speed control map and the flow rate of the exhaust gas 7 in the exhaust flow channel. If the opening degree of the first exhaust passage 11 or the second exhaust passage 13 is adjusted so as to match, the target exhaust gas flow rate can be changed according to the operation state of the diesel engine 1, so that the operation of the diesel engine 1 is performed. Even when the flow rate of the exhaust gas 7 changes due to a state transition, the first flow rate sensor 17, the second flow rate sensor 21, the first flow path adjustment valve 16, and the second flow path adjustment valve 20 are used. Thus, the flow rate of the exhaust gas 7 can be controlled to an appropriate state, and NOx can be suitably reduced and the NOx storage reduction catalysts 10 and 12 can be suitably regenerated.

  The embodiment includes a plurality of first exhaust passages 11 and second exhaust passages 13 equipped with NOx storage reduction catalysts 10 and 12 in parallel, a first passage adjustment valve 16, and a second flow passage. When the first exhaust flow path 11 and the second exhaust flow path 13 are switched by the path adjustment valve 20, one exhaust flow path is formed by the first flow path adjustment valve 16 and the second flow path adjustment valve 20. 11 and 13 are used to use the NOx storage reduction catalysts 10 and 12, and the other exhaust passages 13 and 11 are closed to regenerate the other NOx storage reduction catalysts 12 and 10, so that a plurality of NOx storage reduction catalysts 10 are regenerated. , 12 can be alternately controlled to reduce NOx in the exhaust gas 7 and the NOx storage reduction catalysts 10, 12 can be appropriately controlled to regenerate.

  In the embodiment, the first λ sensor 18 and the second λ sensor 22 that are installed in the exhaust passages 11 and 13 on the downstream side of the NOx storage reduction catalysts 10 and 12 and detect the excess air ratio of the exhaust gas 7 are used. When the first λ sensor 18 and the second λ sensor 22 detect the excess air ratio in the exhaust gas 7 and apply feedback control, the first fuel addition means, the second fuel addition means or / And the first flow path adjustment valve 16 and the second flow path adjustment valve 20 are operated under appropriate conditions, and the NOx storage reduction catalysts 10 and 12 can be suitably regenerated and controlled.

PREFERRED EMBODIMENTS Embodiments, when provided with an O ₂ sensor for detecting the O ₂ concentration in the exhaust gas 7 is installed from the NOx storage reduction catalyst 10, 12 in the exhaust passage 11 and 13 of the downstream exhaust the O ₂ sensor Since the O ₂ concentration in the gas 7 is detected and feedback control is performed, the first fuel addition means, the second fuel addition means or / and the first flow path adjustment valve 16, the second flow path adjustment valve 20. Can be operated under appropriate conditions, and the NOx storage reduction catalysts 10 and 12 can be suitably regenerated.

  Note that the exhaust purification device of the present invention is not limited to the above-described embodiment, and does not include the second exhaust flow path, but only the configuration of the first exhaust flow path, and exhaust gas purification and Of course, the NOx occlusion reduction catalyst may be regenerated, and various changes can be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is the graph compared with the comparative example about the NOx reduction rate.

Explanation of symbols

7 Exhaust gas 10 NOx occlusion reduction catalyst 11 First exhaust passage 12 NOx occlusion reduction catalyst 13 Second exhaust passage 15 Fuel addition nozzle (first fuel addition means)
16 First flow path adjustment valve 17 First flow sensor 18 First λ sensor 19 Fuel addition nozzle (second fuel addition means)
20 Second flow regulating valve 21 Second flow sensor 22 Second λ sensor

Claims (5)

  An exhaust gas purification apparatus equipped with a NOx storage reduction catalyst in the middle of an exhaust passage and configured to reduce and purify NOx by adding fuel as a reducing agent upstream of the NOx storage reduction catalyst, wherein the NOx storage A fuel addition unit that is installed in an exhaust passage upstream of the reduction catalyst and injects fuel, and a passage adjustment valve that is installed in the exhaust passage upstream of the fuel addition unit and adjusts the opening of the exhaust passage And a flow rate sensor for detecting a flow rate of the exhaust gas and sending a control signal to the flow path adjustment valve.   The flow path adjustment valve adjusts the opening degree of the exhaust flow path so that the flow rate of the exhaust gas in the exhaust flow path matches the target exhaust gas flow rate set by the control map of the engine speed. The exhaust emission control device according to 1.   The exhaust emission control device according to claim 1 or 2, wherein a plurality of exhaust passages equipped with NOx occlusion reduction catalyst are provided in parallel, and the exhaust passage is switched by a passage adjustment valve.   The exhaust emission control device according to any one of claims 1 to 3, further comprising a λ sensor that is installed in an exhaust passage downstream of the NOx storage reduction catalyst and detects an excess air ratio of exhaust gas. An exhaust emission control device as claimed in any one of claims 1 to 3, comprising the O ₂ sensor from the NOx storage-reduction catalyst is disposed in an exhaust passage on the downstream side detects the O ₂ concentration in the exhaust gas .

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