JP2013002314A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a selective reduction catalyst, which is poisoned with HC, by utilizing existing equipment.SOLUTION: In an exhaust emission control device, a selective reduction catalyst 5, which reduces and controls NOx by using ammonia as a reducing agent, is provided midway through an exhaust pipe 4; a particulate filter 13 is provided in a front stage thereof; a burner 14 is provided in a front stage thereof; and a urea solution addition device 12 for adding a urea solution 11 into exhaust gas 3 is provided between the particulate filter 13 and the selective reduction catalyst 5. A control unit 18 for controlling the combustion of the burner 14 includes: an HC adsorption determination section which detects that the amount of adsorption of HC into the selective reduction catalyst 5 reaches a predetermined value or above; a long-time idling determination section which detects that duration time of an idling state of a vehicle reaches a predetermined value or above; and a burner ignition determination section which brings about the combustion of the burner 14 when either the long-time idling determination section or the HC adsorption determination section detects that either the duration time of the idling state of the vehicle or the amount of adsorption of HC into the selective reduction catalyst 5 reaches the predetermined value or above.

Description

  The present invention relates to an exhaust emission control device.

  Conventionally, in a diesel engine, a particulate filter is provided in the middle of an exhaust pipe through which exhaust gas flows, and particulate matter (particulate matter) contained in the exhaust gas is collected through the particulate filter. However, in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust, so an oxidation catalyst that uses Pt, Pd, or the like as an active species is used as a particulate filter. It is made to carry in one.

  That is, if such a particulate filter carrying an oxidation catalyst is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at a lower exhaust temperature than in the past. It becomes possible.

  However, even when such a particulate filter is adopted, the trapped amount exceeds the processing amount of particulates in the operation region where the exhaust temperature is low, so operation at such a low exhaust temperature is required. If the state continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is attached to the front stage of the particulate filter, and the particulate filter is forced by adding fuel to the exhaust gas upstream of the oxidation catalyst when the particulate adsorption amount has increased. It is considered to play.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the particulate filter immediately after that is raised, the particulates are burned out, and the particulate filter is regenerated.

  However, the catalyst bed in which the oxidation catalyst in the previous stage can exhibit sufficient catalytic activity in a vehicle with an operation state where the operation state with a low exhaust temperature continues for a long time such as an urban route bus that travels only on a congested road There is a problem that the particulate filter cannot be efficiently regenerated within a short time because it is difficult to raise the temperature to the temperature and the oxidation reaction of the added fuel in the oxidation catalyst is not activated.

  For this reason, in recent years, a post-processing burner system has been adopted in which a burner is provided on the inlet side of the particulate filter, and the particulate filter is efficiently regenerated in a short time by combustion of the burner regardless of the operating state of the vehicle. It has started (for example, refer to the following Patent Document 1).

JP 2009-91909 A

  However, if a selective reduction catalyst having the property of selectively reacting NOx with ammonia even in the presence of oxygen is provided downstream of the particulate filter, the HC generated in the diesel engine and burner is removed by the particulate filter. There is a problem that it passes through the catalyst and reaches the selective catalytic reduction catalyst, which poisons the selective catalytic reduction catalyst and causes a reduction in NOx purification performance.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to enable recovery of a selective catalytic reduction catalyst poisoned by HC using existing equipment.

  The present invention provides a selective reduction catalyst for reducing and purifying NOx using ammonia as a reducing agent in the middle of an exhaust pipe, a particulate filter in front of the selective reduction catalyst, and a burner in front of the particulate filter. A control device for controlling combustion of the burner in an exhaust gas purification device provided with a urea water addition device for adding urea water to the exhaust gas between the particulate filter and the selective catalytic reduction catalyst, HC adsorption amount determination unit for detecting that the amount of HC adsorbed on the selective catalytic reduction catalyst exceeds a specified value, and long-term idling for detecting that the duration of the idling state of the vehicle exceeds a specified value The burner is burned when a determination value or more is detected by the determination unit, the long-term idling determination unit, or the HC adsorption amount determination unit. And a burner ignition determination unit.

  Thus, in this way, when the HC adsorption amount determination unit detects that the amount of HC adsorption to the selective catalytic reduction catalyst exceeds the specified value, or when the idling determination unit for a long time detects idling of the vehicle. When it is detected that the duration of the state exceeds the specified value, the burner ignition determination unit burns the burner and sends high-temperature exhaust gas to the selective catalytic reduction catalyst via the particulate filter. The catalyst bed temperature of the reduction catalyst is increased to exceed the HC desorption temperature, HC adsorbed on the selective reduction catalyst is desorbed and HC poisoning is eliminated, and the NOx purification performance of the selective reduction catalyst is greatly improved. Will be recovered.

  At this time, since the HC adsorbed and accumulated in the particulate filter in the operation state where the exhaust temperature is low is also desorbed by the heating by the burner combustion, a large amount of HC is accumulated in the particulate filter. The situation is also avoided at the same time, and a situation in which a large amount of HC is desorbed at once and white smoke is generated at the rear of the vehicle when the driving state is changed to a high exhaust temperature is prevented.

  In the present invention, the HC adsorption amount determination unit estimates and integrates the HC adsorption amount to the selective catalytic reduction catalyst based on the operating conditions of the engine and the burner, and monitors the inlet side exhaust temperature of the selective catalytic reduction catalyst. It is preferable that the integration of the HC adsorption amount is reset when a detection at a predetermined temperature or more has passed for a predetermined time, and the idling determination unit for a long time further includes a detection signal for the engine speed. Determining whether or not the engine is in an idling state based on a combination with any one or more of an engine load detection signal, a neutral switch detection signal, a side brake switch detection signal, and a vehicle speed sensor detection signal; It is preferable that the duration is measured when the vehicle is in the idling state.

  According to the above-described exhaust purification device of the present invention, when the amount of HC adsorbed on the selective catalytic reduction catalyst is considered to be a specified value or more, or when the duration of the idling state of the vehicle has exceeded the specified value, the existing The catalyst bed temperature of the selective catalytic reduction catalyst can be increased using the burner of this type, and the HC adsorbed on the selective catalytic reduction catalyst can be desorbed to eliminate HC poisoning. Since the purification performance can be greatly recovered, and the HC adsorbed and stored in the particulate filter in the operating state with a low exhaust temperature can be desorbed by the heating by the burner combustion, the particulate filter It is possible to achieve an excellent effect that it is possible to prevent a situation in which a large amount of HC accumulated in the vehicle is detached at a stretch and white smoke is generated behind the vehicle.

It is the schematic which shows an example of the form which implements this invention. It is the figure which showed typically the control system regarding control of the burner of this form example. It is a flowchart which shows the specific control procedure in the control apparatus of FIG.

  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 exhaust purification apparatus of this embodiment, the exhaust pipe 4 through which the exhaust gas 3 discharged from the diesel engine 1 through the exhaust manifold 2 flows is shown. In addition, a selective catalytic reduction catalyst 5 having the property of selectively reacting NOx with ammonia even in the presence of oxygen is provided.

  An injection nozzle 6 is installed on the inlet side of the selective reduction catalyst 5, and urea water supply including a urea water injection valve 7 is provided between the injection nozzle 6 and a urea water tank 8 provided at a required place. The urea water 11 (reducing agent) in the urea water tank 8 is connected to the selective catalytic reduction catalyst 5 via the urea water injection valve 7 by driving a supply pump 10 connected in the middle of the urea water supply line 9. The urea water injection device 12 is configured by the urea water injection valve 7, the urea water tank 8, the urea water supply line 9, and the supply pump 10.

  A particulate filter 13 for collecting and removing particulates from the exhaust gas 3 in the exhaust pipe 4 upstream of the urea water 11 addition position (opening position of the injection nozzle 6) by the urea water addition device 12 is provided. A burner 14 is provided in front of the particulate filter 13 to inject an appropriate amount of fuel to ignite and burn, and the burner 14 is a fuel injection nozzle that injects an appropriate amount of fuel (not shown). And an ignition plug for igniting the fuel injected from the injection port.

Further, upstream of the addition position of urea water 11 (opening position of the injection nozzle 6) between the particulate filter 13 and the selective reduction catalyst 5, unburned HC in the exhaust gas 3 is oxidized and An oxidation catalyst 15 that promotes an oxidation reaction of NO in the exhaust gas 3 to NO ₂ is interposed.

In the example shown here, immediately after the selective catalytic reduction catalyst 5, an NH ₃ slip catalyst 16 that oxidizes surplus ammonia as a countermeasure for leaked ammonia is provided.

  In this embodiment, a temperature sensor 17 for measuring the temperature of the exhaust gas 3 is provided on the inlet side of the selective catalytic reduction catalyst 5, and a detection signal 17a of the temperature sensor 17 is an engine control computer ( It is input to a control device 18 constituting an ECU (Electronic Control Unit).

  The control device 18 is also responsible for control relating to fuel injection in the diesel engine 1, and more specifically, a detection signal 20 a from an accelerator sensor 20 that detects the accelerator opening as a load of the diesel engine 1, Based on the detection signal 21 a from the rotation sensor 21 that detects the rotational speed of the diesel engine 1, a fuel injection signal 19 a is output to the fuel injection device 19 that injects fuel into each cylinder of the diesel engine 1. Yes.

  Here, the fuel injection device 19 is composed of a plurality of injectors (not shown) provided for each cylinder, and the solenoid valve of each injector is controlled to open by the fuel injection signal 19a, and the fuel injection timing. In addition, the injection amount is appropriately controlled.

  Further, the control device 18 is also responsible for controlling the combustion of the burner 14, and it is necessary to perform forced regeneration on the assumption that the accumulated amount of particulates in the particulate filter 13 exceeds an allowable amount. When it is determined that the burner 14 is ignited and combusted by the combustion command signal 14a.

  There are various methods for estimating the amount of accumulated particulates. For example, the basic generation amount of particulates based on the current operating state of the diesel engine 1 is estimated, and this basic generation amount is calculated. Multiply the correction factors considering various conditions related to the generation of particulates and subtract the particulate processing amount in the current operation state to obtain the final generation amount, and accumulate this final generation amount every moment Thus, it is possible to estimate the amount of accumulated particulates.

  As schematically shown in FIG. 2, the control device 18 includes an HC adsorption amount determination unit 25 that detects that the adsorption amount of HC to the selective catalytic reduction catalyst 5 exceeds a specified value, and a vehicle The long-time idling determination unit 26 that detects that the duration of the idling state has exceeded a specified value, and the long-time idling determination unit 26 and the HC adsorption amount determination unit 25 detect more than the specified value. And a burner ignition determination unit 27 for burning the burner 14 by outputting a combustion command signal 14a from the control device 18 when being operated, and not only when the particulate filter 13 is forcibly regenerated, but also idling for a long time. The burner 14 is burned even when the selective catalytic reduction catalyst 5 is considered to be poisoned with HC by normal operation.

  That is, in the control device 18 that is in charge of control regarding fuel injection and combustion of the burner 14 in the diesel engine 1, all the information regarding the operation status such as the fuel injection amount (indicated value) and the ignition failure of the burner 14 is grasped. Since it is possible to estimate the amount of unburned HC generated due to the operation of the diesel engine 1 and the burner 14, it passes through the particulate filter 13 and the oxidation catalyst 15 of the HC and is selectively reduced. The amount of HC adsorbed on the selective reduction catalyst 5 is monitored by the HC adsorption amount determination unit 25 by calculating the ratio of the amount adsorbed by the catalyst 5 and accumulating the proportion.

  However, in the HC adsorption amount determination unit 25, the exhaust temperature on the inlet side of the selective catalytic reduction catalyst 5 is monitored based on the detection signal 17a of the temperature sensor 17, and the detection of the predetermined temperature or higher is detected for a predetermined time or longer. When the time has elapsed, the integration of the HC adsorption amount is reset on the assumption that the HC adsorbed on the selective catalytic reduction catalyst 5 has been released.

  The relationship between the operating conditions of the diesel engine 1 and the burner 14 and the amount of unburned HC, and what percentage of the generated HC is adsorbed by the selective catalytic reduction catalyst 5 is the same in advance. Can be ascertained through experiments, and a calculation program may be established based on the results of the experiments.

  Further, when the long-time idling determination unit 26 detects that the duration of the idling state of the vehicle exceeds a specified value, the control device 18 includes the temperature sensor 17, the accelerator sensor 20, and the rotation described above. In addition to the sensor 21, a detection signal 22a from a neutral switch 22 for detecting that the gear position is in the neutral position, a side brake switch 23 for detecting that the side brake is applied, and a vehicle speed sensor 24 for detecting the vehicle speed. , 23a, 24a are input, and based on these signals, whether or not the vehicle is in the idling state is determined by the long-time idling determination unit 26, and is in the idling state. When it is determined that, the duration is timed.

  More specifically, the rotation sensor 21 confirms that the engine speed is within a relatively low predetermined rotational speed range, the accelerator sensor 20 confirms that the accelerator is off (load is zero), and the neutral switch 22 changes the gear position to the neutral position. If it is confirmed that the side brake is being pulled by the side brake switch 23 and the vehicle speed is confirmed to be zero by the vehicle speed sensor 24, if the current driving state is in the idling state, It is determined by the idling determination unit 26, and time measurement by a timer or the like is started from that point.

  Here, regarding the determination of the idling state, not all signals from these sensors and switches are necessarily required, but at least the rotation sensor 21, the accelerator sensor 20, the neutral switch 22, the side brake switch 23, the vehicle speed. It is possible to determine whether or not the vehicle is in an idling state based on a signal detected by a combination with one or more of the sensors 24.

  FIG. 3 is a flowchart showing a specific control procedure in the control device 18. In step S1, the adsorption amount of HC in the selective catalytic reduction catalyst 5 is monitored and accumulated every moment, and in the next step S2, the adsorption of the HC. It is determined whether or not the amount is equal to or greater than a specified value, and the same determination is repeated until the amount is equal to or greater than the specified value.

  On the other hand, the continuation time when the vehicle is in the idling state is measured in step S3, and it is determined whether or not the continuation time when the vehicle is in the idling state in step S4 is equal to or greater than the specified value. The same determination is repeated until

  If detection of a specified value or more is made in either step S2 or step S4, the detection is confirmed in step S5, the process proceeds to the next step S6, the output of the combustion command signal 14a is determined, and the burner 14 is determined. Will be burned.

  The burner 14 is combusted when the HC adsorbed on the selective catalytic reduction catalyst 5 has been detached when the detection of a predetermined temperature or more has passed for a predetermined time or more based on the detection signal 17a of the temperature sensor 17. The operation is stopped in step S7, and at this time, the accumulated HC adsorption amount and the idling duration time are reset.

  Thus, if the exhaust gas purification apparatus is configured in this way, the HC adsorption amount determination unit 25 detects that the adsorption amount of HC to the selective catalytic reduction catalyst 5 has exceeded a specified value, or for a long time. When the idling determination unit 26 detects that the duration of the idling state of the vehicle exceeds the specified value, the burner ignition determination unit 27 burns the burner 14 and the high-temperature exhaust gas 3 passes through the particulate filter 13. To the selective catalytic reduction catalyst 5, the catalyst bed temperature of the selective catalytic reduction catalyst 5 is increased to be higher than the HC desorption temperature, and the HC adsorbed on the selective catalytic reduction catalyst 5 is desorbed and the HC The poison is eliminated and the NOx purification performance of the selective catalytic reduction catalyst 5 is greatly recovered.

  At this time, since the HC adsorbed and stored in the particulate filter 13 in the operation state where the exhaust temperature is low is also desorbed by heating due to the combustion of the burner 14, a large amount of HC is stored in the particulate filter 13. This situation is avoided at the same time, and a situation where a large amount of HC is desorbed at a stretch and white smoke is generated at the rear of the vehicle when the driving state is changed to a high exhaust temperature is prevented.

  Therefore, according to the above-described embodiment, when the amount of HC adsorbed on the selective catalytic reduction catalyst 5 is considered to be equal to or greater than the specified value, or when the duration of the idling state of the vehicle has exceeded the specified value, the existing burner 14 can be used to increase the catalyst bed temperature of the selective catalytic reduction catalyst 5 and desorb HC adsorbed on the selective catalytic reduction catalyst 5 to eliminate HC poisoning. NOx purification performance can be greatly recovered, and furthermore, the HC adsorbed and accumulated in the particulate filter 13 in the operation state where the exhaust temperature is low can be desorbed by heating due to the combustion of the burner 14. Further, it is possible to prevent a situation in which a large amount of HC accumulated in the particulate filter 13 is desorbed all at once and white smoke is generated behind the vehicle.

  The exhaust emission control device according to the present invention is not limited to the above-described embodiment, but is also used in combination with a control for burning the burner in order to activate the selective catalytic reduction catalyst at the time of cold start or the like. Of course, various modifications can be made without departing from the scope of the present invention.

1 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 3 Exhaust gas 4 Exhaust pipe 5 Selective reduction type catalyst 11 Urea water 12 Urea water addition apparatus 13 Particulate filter 14 Burner 14a Combustion command signal 17 Temperature sensor 17a Detection signal 18 Control apparatus 20 Accelerator sensor 20a Detection signal 21 Rotation sensor 21a Detection signal 22 neutral switch 22a detection signal 23 side brake switch 23a detection signal 24 vehicle speed sensor 24a detection signal 25 HC adsorption amount determination unit 26 long time idling determination unit 27 burner ignition determination unit

Claims (3)

  A selective reduction catalyst for reducing and purifying NOx using ammonia as a reducing agent is provided in the middle of the exhaust pipe, and a particulate filter is provided in front of the selective reduction catalyst, and a burner is provided in the upstream of the particulate filter. In the exhaust gas purification apparatus provided with urea water adding devices for adding urea water to the exhaust gas between the curate filter and the selective reduction catalyst, the control device for controlling the combustion of the burner includes the selective reduction type An HC adsorption amount determination unit that detects that the amount of HC adsorbed on the catalyst is equal to or greater than a specified value; a long-time idling determination unit that detects that the duration of the idling state of the vehicle is equal to or greater than the specified value; Burner ignition that burns the burner when detection of a specified value or more is detected by either the long-term idling determination unit or the HC adsorption amount determination unit An exhaust emission control device comprising a determination unit.   The HC adsorption amount determination unit estimates and accumulates the amount of HC adsorption to the selective catalytic reduction catalyst based on the operating conditions of the engine and burner, and monitors the exhaust temperature on the inlet side of the selective catalytic reduction catalyst to detect a predetermined temperature or higher. 2. The exhaust emission control device according to claim 1, wherein the exhaust gas purification device is configured to reset the integration of the HC adsorption amount when a predetermined time elapses.   The combination of the engine speed detection signal and the engine load detection signal, the neutral switch detection signal, the side brake switch detection signal, or the vehicle speed sensor detection signal when the long-term idling determination unit The exhaust emission control device according to claim 1, wherein the exhaust gas purification device is configured to determine whether or not the vehicle is in an idling state on the basis of the engine time and to measure the duration when the vehicle is in the idling state.

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