JP2006037857A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device preventing temperature drop of a post-treatment means and preventing deterioration of drivability. <P>SOLUTION: This device is provided with a post-treatment means 12 provided in an exhaust pipe 11 in which exhaust gas from an engine 1 circulates, EGR means 15, 16, 17 taking part of exhaust gas 9 out of an exhaust manifold 10 of the engine 1 and re-circulate the same to an intake manifold 7 side of the engine, and a fuel adding means 22 arranged in an upstream of the EGR means 15, 16, 17 and the post treatment means 12 and adding fuel. When fuel addition by the fuel adding means 22 is stopped, flow rate of fresh air introduced to the engine 1 is limited and exhaust gas or/and fresh air are circulated via the EGR means 15, 16, 17. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device applied to an engine such as a diesel engine.

  Particulate matter (particulate matter) discharged from a diesel engine as an internal combustion engine is mainly composed of carbonaceous soot and SOF (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. As a component, it is composed of a small amount of sulfate (sulfate component), but as a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which exhaust gas flows. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust. For example, an appropriate amount for platinum-supported alumina A catalyst regeneration type particulate filter in which an oxidation catalyst formed by adding a rare earth element such as cerium is integrally supported is being put to practical use.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  In addition, the engine is equipped with an EGR pipe, EGR valve, etc. so that a part of the exhaust gas is extracted from the exhaust manifold and recirculated to the intake manifold side of the engine. When regenerating the particulate filter, add fuel. The exhaust temperature is raised by adding fuel by means and closing the EGR valve to stop the exhaust gas recirculation.

Here, some examples of such exhaust purification devices that are general examples have already been disclosed as patent publications (see, for example, Patent Document 1).
JP 2003-155915 A

  On the other hand, together with such a catalyst regeneration type particulate filter, a selective reduction type catalyst having the property of selectively reacting NOx with a reducing agent even in the presence of oxygen is provided in the middle of an exhaust pipe through which exhaust gas flows. Such a selective catalytic reduction catalyst, by adding a necessary amount of reducing agent from the upstream side, causes a reducing reaction between the reducing agent and NOx (nitrogen oxide) in the exhaust gas, As a result, the NOx emission concentration can be reduced.

  However, when the driver turns off the accelerator by a shift change or the like during traveling, the addition of fuel injected into each cylinder of the engine is stopped and the intake throttle valve of the intake pipe that introduces fresh air into the engine Since the air is fully opened, the fresh air does not burn and flows down to the post-treatment means such as a catalyst regeneration type particulate filter or selective reduction type catalyst, causing the temperature of the post-treatment means to drop, and the oxidation of the particulate filter. There is a problem that the exhaust gas purification ability cannot be suitably maintained because the temperature of the catalyst or the selective reduction catalyst falls below the activation temperature range (temperature window).

  On the other hand, it is conceivable to limit the flow rate of fresh air by closing the intake throttle valve of the intake pipe in order to prevent the temperature of the post-processing means from decreasing. When the accelerator is turned off, etc., there is a problem that drivability is remarkably deteriorated.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust purification device that prevents a decrease in temperature of the post-processing means and prevents deterioration of drivability.

The present invention includes post-processing means equipped in an exhaust pipe through which exhaust gas from the engine flows, EGR means for extracting a part of the exhaust gas from the exhaust manifold of the engine and recirculating it to the intake manifold side of the engine, A fuel addition means for adding fuel disposed upstream of the post-processing means and the EGR means;
When the fuel addition by the fuel addition means is stopped, the flow rate of fresh air introduced into the engine is limited and exhaust gas or / and fresh air is circulated through the EGR means. The present invention relates to an exhaust purification device.

  In addition, an intake throttle means for adjusting the flow rate of fresh air is provided, and an EGR valve is provided in the EGR means. When the addition of fuel by the fuel addition means is stopped, the flow rate of fresh air is limited by the intake throttle means. At the same time, the exhaust gas is preferably circulated through the EGR means by the EGR valve.

  Furthermore, it is preferable that the EGR cooler provided in the EGR means is configured as a heater so as to raise the temperature of the fresh air and / or exhaust gas that has flowed.

  Thus, when the addition of fuel by the fuel addition means is stopped in this way, the flow rate of fresh air introduced into the engine is limited, and the exhaust gas or / and fresh air is sent from the exhaust manifold to the EGR means. Therefore, it is possible to prevent the exhaust gas or / and fresh air from flowing into the post-processing means and prevent the temperature of the post-processing means from decreasing. Even when the flow rate of fresh air to the engine is limited, exhaust gas or / and fresh air is circulated from the exhaust manifold to the intake manifold via the EGR means, so that engine braking is suppressed and drivability is reduced. Can be prevented.

  In addition to the intake throttle means for adjusting the flow rate of fresh air, the EGR means is provided with an EGR valve, and when the addition of fuel by the fuel addition means is stopped, the flow rate of fresh air is restricted by the intake throttle means, and EGR If the exhaust gas is circulated through the EGR means by the valve, the exhaust gas or / and the fresh air can be circulated by closing the intake throttle means and opening the EGR valve. It is possible to easily suppress the flow into the means and to suitably prevent the temperature of the post-processing means from decreasing. In addition, the flow rate of fresh air to the engine is limited by the intake throttle means, and exhaust gas or / and fresh air are circulated from the exhaust manifold to the intake manifold via the EGR means by the EGR valve, so that engine braking can be easily generated. It is possible to suppress the deterioration of drivability.

  If the EGR cooler provided in the EGR means is configured to raise the temperature of the incoming fresh air and / or exhaust gas as a heater, the incoming fresh air or / and exhaust gas can be heated in advance from the outside air, so that the circulating exhaust gas Alternatively, the temperature of the fresh air can be maintained at a predetermined temperature or higher, and a significant temperature drop of the post-treatment means when exhaust gas or / and fresh air flows into the post-treatment means can be prevented.

  According to the above-described exhaust purification device of the present invention, when the fuel addition by the fuel addition means is stopped, the flow rate of fresh air introduced into the engine is limited, and exhaust gas or / and fresh air is removed from the exhaust manifold by EGR. Since it circulates to the intake manifold via the means, it is possible to prevent the exhaust gas or / and fresh air from flowing into the post-treatment means, thereby preventing the temperature of the post-treatment means from decreasing and preventing the drivability from deteriorating. An excellent effect can be achieved.

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

  1 to 5 show an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine equipped with a turbocharger 2, and fresh air 4 introduced from an air cleaner 3 is taken into an intake pipe. 5 is sent to the compressor 2 a of the turbocharger 2, and the fresh air 4 pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and further from the intercooler 6 to the intake manifold 7. The gas 4 is guided and distributed to each cylinder 8 of the diesel engine 1 (in FIG. 1, the case of in-line 6 cylinders is illustrated).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b is discharged to the exhaust pipe 11 (exhaust gas). It is designed to be discharged out of the vehicle through the flow path).

  In the middle of the exhaust pipe 11, post-processing means 12 for purifying exhaust gas in a predetermined activation temperature range (temperature window) is provided. Here, one of the post-processing means 12 includes a particulate filter (DPF) that collects and burns the particulate, and the other is DPNR (Diesel Particulate and NOx Reduction). Some have a NOx reduction catalyst that once adsorbs NOx to a predetermined catalyst and burns particulates with highly reactive active oxygen or the like generated at that time. Another is a reducing agent such as ammonia. There are some which are provided with a selective reduction catalyst that treats NOx by reacting with a reducing agent such as ammonia on the catalyst as SCR (Selective Catalytic Reduction) by blowing in. The post-processing means 12 is not limited to the above example, and is not particularly limited as long as the exhaust gas is purified within a predetermined activation temperature range (temperature window).

  Further, in the example shown in FIG. 1, the EGR pipe 15 of the EGR means extends between one end of the exhaust manifold 10 in the direction in which the cylinders 8 are arranged and one end of the intake pipe 5 connected to the intake manifold 7. And a part of the exhaust gas 9 extracted from the exhaust manifold 10 is recirculated to the intake pipe 5 through the water-cooled EGR cooler 16 and the EGR valve 17 of the EGR means. The exhaust gas 9 recirculated to the side suppresses the combustion of fuel in each cylinder 8 and lowers the combustion temperature so that the generation of NOx can be reduced.

  Further, a temperature sensor 18 for measuring the temperature of the exhaust gas 9 as a substitute value of the catalyst bed temperature is provided in front of the post-processing means 12, and the temperature signal 18a of the temperature sensor 18 is an engine control computer ( It is input to a control device 19 constituting an ECU (Electronic Control Unit). Here, the arrangement of the temperature sensor 18 is not limited to the position before the post-processing means 12 and is not particularly limited as long as the catalyst bed temperature can be measured.

  Since this control device 19 also serves as an engine control computer, it is also responsible for control relating to fuel injection. More specifically, the control device 19 detects an accelerator opening as a load of the diesel engine 1 ( Fuel addition means for injecting fuel into each cylinder 8 of the diesel engine 1 based on the accelerator opening signal 20a from the load sensor) and the rotation speed signal 21a from the rotation sensor 21 that detects the engine speed of the diesel engine 1 A fuel injection signal 22 a is output to the fuel injection device 22. Here, the fuel injection device 22 is composed of a plurality of injectors 23 provided for each cylinder 8, and the electromagnetic valves of these injectors 23 are appropriately controlled to open by the fuel injection signal 22a, and the fuel is supplied. The injection timing (valve opening timing) and the injection amount (valve opening time) are appropriately controlled.

  Further, in the control device 19, an intake throttle valve 24 of the intake throttle means provided in the intake pipe 5 downstream of the intercooler 6, and an exhaust brake 25 provided in the exhaust pipe 11 upstream of the post-processing means 12; Opening command signals 24a, 25a and 17a for commanding the opening of the EGR pipe 15 and the EGR valve 17 are output.

  Further, in the control device 19, the fuel injection signal 22a in the normal mode is determined based on the accelerator opening signal 20a and the rotation speed signal 21a. Depending on an example of the post-processing means 12, the particulate filter When it becomes necessary to perform forced regeneration, the normal mode is switched to forced regeneration mode, and the non-ignition which is slower than the compression top dead center following the main injection of fuel performed near the compression top dead center (crank angle 0 °). A fuel injection signal 22a that performs post injection at the timing is determined.

  Furthermore, when the driver turns off the accelerator by a shift change or the like during traveling, the control device 19 includes a flow process as shown in FIG.

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

  That is, when the driver turns off the accelerator during traveling, for example, fuel addition is stopped by the fuel injection device 22 of the fuel addition means, so in the control device 19, as shown in FIG. It is determined in advance whether or not the catalyst bed temperature is higher than a predetermined activation temperature range (temperature window) by the temperature sensor 18 or the like (step S1). 20 and the rotation sensor 21 are used to determine whether or not fuel addition is stopped (whether there is no fuel injection) (step S2). If the fuel addition stops, the intake throttle valve 24 of the intake throttle means is closed. The EGR valve 17 of the EGR means is opened (step S3), and the process returns to the first stage by return. Subsequently, after the intake throttle valve 24 is closed and the EGR valve 17 is opened, the start of fuel addition is determined by the accelerator sensor 20, the rotation sensor 21 and the like. The treatment means 12 purifies the exhaust gas.

  Here, when the catalyst bed temperature is higher than a predetermined activation temperature range (temperature window) in the first determination (step S1), the catalyst bed temperature is lowered simultaneously with returning to the first stage by return. As an example of the processing, feedback processing is performed based on the catalyst bed temperature, the opening of the intake throttle valve 24 is widened in a state where fuel addition is stopped, and a large amount of fresh air is introduced to increase the catalyst bed temperature. There is something to lower. In step S1 of FIG. 2, the upper limit of the activation temperature range (temperature window) is set to 550 ° C., and determination is made based on whether the catalyst bed temperature is 550 ° C. or less.

  When the intake throttle valve 24 of the intake throttle means is closed and the EGR valve 17 of the EGR means is opened (step S3), the intake throttle valve 24 limits the flow rate of fresh air introduced into the engine. 3, the EGR valve 17 causes the exhaust gas to circulate from the exhaust manifold 10 to the intake manifold 7 via the EGR pipe 15 and the EGR cooler 16, and further from the cylinder 8 to the exhaust manifold 10 and not flow down to the post-processing means 12. Like that. At this time, depending on the type of the post-processing means 12, the intake throttle valve 24 may be fully closed or set to a predetermined opening. If the intake throttle valve 24 is not fully closed, a mixed gas of exhaust gas and fresh air may be circulated from the exhaust manifold 10 to the intake manifold 7 via the EGR pipe 15 and the EGR cooler 16. Furthermore, since the EGR cooler 16 has a temperature of 70 ° C. to 90 ° C. due to engine cooling water, when fresh air close to the temperature of the outside air flows in, the EGR cooler 16 acts as a heater. The temperature of the gas or / and the exhaust gas is rising. Further, in the case of a turbo engine (TI engine) equipped with the intercooler 6, it is preferable to throttle the intake throttle valve 24 to the minimum necessary level, not fully open. Note that the opening and closing of the exhaust brake 25 is not suitable because it does not follow the fuel by stopping the addition of fuel and generates noise.

  Thus, when the fuel addition by the fuel addition means is stopped, the flow rate of fresh air introduced into the diesel engine 1 is limited, and exhaust gas or / and fresh air is sucked from the exhaust manifold 10 via the EGR means. Since it is circulated to the manifold 7, the exhaust gas or / and fresh air are prevented from flowing into the post-processing means 12 to prevent the temperature of the post-processing means 12 from decreasing, and as a result, the exhaust gas purification ability is maintained well. can do. Here, when the actual measurement data is shown with the post-processing means 12 as the NOx reduction catalyst of DPNR, as shown in FIG. On the other hand, in the example of the present invention, the temperature can be increased to 250 ° C. or more in many times even under the same conditions. In addition, when it becomes 350 degreeC or more, it controls so that it may be 350 degreeC or less noting that it is more than an active temperature range. Further, as shown in FIG. 5, in the present invention, the NOx reduction rate can be made suitable by setting the catalyst bed temperature to 250 ° C. or higher. Furthermore, when regenerating the particulate filter, it is preferable to control to about 220 ° C. so that post injection or the like can be performed.

  Further, according to the present embodiment, even when the flow rate of fresh air to the diesel engine 1 is limited by an operation of turning off the accelerator by a shift change or the like during acceleration during traveling, the exhaust gas and / or fresh air is limited. Is circulated from the exhaust manifold 10 to the intake manifold 7 via the EGR means, so that the occurrence of engine braking can be suppressed and deterioration of drivability can be prevented.

  In addition to the intake throttle valve 24 of the intake throttle means for adjusting the flow rate of fresh air, the EGR means is provided with the EGR valve 17, and when the addition of fuel by the fuel injection device 22 of the fuel addition means is stopped, the intake throttle means When the exhaust air flow is restricted by the intake throttle valve 24 and the exhaust gas is circulated through the EGR pipe 15 of the EGR means by the EGR valve 17, the exhaust gas or / and the fresh air is circulated. Since the exhaust gas or / and the fresh air can be easily suppressed from flowing into the post-processing means 12, the temperature drop of the post-processing means 12 can be suitably prevented, and as a result In addition, it is possible to maintain the exhaust gas purification ability more satisfactorily. In addition, the flow rate of fresh air to the diesel engine 1 is limited by the intake throttle valve 24 of the intake throttle means, and exhaust gas or / and fresh air is sucked from the exhaust manifold 10 via the EGR pipe 15 of the EGR means by the EGR valve 17. Since it circulates to the manifold 7, it is possible to easily suppress the occurrence of engine braking and to suitably prevent deterioration of drivability.

  If the EGR cooler 16 provided in the EGR means is configured as a heater to raise the temperature of the incoming fresh air and / or exhaust gas, the incoming fresh air or / and exhaust gas can be heated in advance from the outside air, and therefore circulates. The temperature of the exhaust gas or / and fresh air can be maintained at a predetermined temperature or higher, and a significant temperature drop of the post-processing means 12 when the exhaust gas or / and fresh air flows into the post-processing means 12 can be prevented.

  The exhaust emission control device of the present invention is not limited only to the above-described embodiment, but when the fuel addition is stopped is limited to a case where the accelerator is turned off by a shift change or the like during traveling. However, other states may be used as long as the fuel addition is stopped, and various changes can be made without departing from the scope of the present invention.

It is the schematic which shows the state of the normal flow of waste gas in the embodiment which implements this invention. It is a flowchart which judges stop of addition of fuel and controls an intake throttle valve and an EGR valve. It is the schematic which shows the state which circulates exhaust gas and / or fresh air in the embodiment which implements this invention. It is a graph which shows the difference of the catalyst bed temperature in a prior art example and this invention. It is a graph which shows the NOx reduction rate in the catalyst bed temperature of this invention.

Explanation of symbols

1 Diesel engine (engine)
7 Intake manifold 9 Exhaust gas 10 Exhaust manifold 11 Exhaust pipe 12 Post-processing means 15 EGR pipe (EGR means)
16 EGR cooler (EGR means)
17 EGR valve (EGR means)
22 Fuel injector (fuel addition means)
24 Intake throttle valve (intake throttle means)

Claims (3)

Post-processing means equipped in an exhaust pipe through which exhaust gas from the engine flows, EGR means for extracting a part of the exhaust gas from the exhaust manifold of the engine and recirculating it to the intake manifold side of the engine, and the post-processing means And fuel addition means for adding fuel disposed upstream of the EGR means,
When the fuel addition by the fuel addition means is stopped, the flow rate of fresh air introduced into the engine is limited and exhaust gas or / and fresh air is circulated through the EGR means. Exhaust purification device.   In addition to the intake throttle means for adjusting the flow rate of fresh air, the EGR means is provided with an EGR valve, and when the addition of fuel by the fuel addition means is stopped, the flow rate of fresh air is limited by the intake throttle means, The exhaust emission control device according to claim 1, wherein exhaust gas is circulated by the EGR valve via the EGR means.   The exhaust emission control device according to claim 1 or 2, wherein an EGR cooler provided in the EGR means is configured to raise the temperature of fresh air or / and exhaust gas that has flowed in as a heater.

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