JP2010261329A - Exhaust purification device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust purification device capable of surely detecting abnormality of a post-catalyst NOx sensor arranged on the downstream side of a selective reduction type catalyst, without stopping addition of urea as a reducing agent. <P>SOLUTION: This exhaust purification device has a control device 24 as an abnormality determining means for determining the abnormality of the post-catalyst NOx sensor 31, by mutually comparing a post-catalyst NOx concentration 31a detected by the post-catalyst NOx sensor 31 with a pre-catalyst NOx concentration 30a detected by a pre-catalyst NOx sensor 30 arranged on the upstream side of the selective reduction type catalyst 10, or an engine discharge NOx calculation value determined based on an operation state of a diesel engine 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Conventionally, a diesel engine is equipped with a selective reduction type catalyst having a property of selectively reacting NOx (nitrogen oxide) with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, A necessary amount of a reducing agent is added upstream of the selective catalytic reduction catalyst so that the reducing agent undergoes a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

  In general, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia as a reducing agent is already widely known. In recent years, the use of non-toxic urea water as a reducing agent has been studied because of the problems associated with running the vehicle itself.

  That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas, and NOx in the exhaust gas is converted to ammonia on the selective catalytic reduction catalyst. It will be reduced and purified well by ammonia.

  By the way, when using the selective catalytic reduction catalyst, it is necessary to control the amount of reducing agent added to the selective catalytic reduction catalyst to an appropriate amount. Therefore, a NOx sensor is provided on the downstream side of the selective catalytic reduction catalyst, and the NOx The amount of reducing agent is controlled in accordance with the NOx concentration in the exhaust gas detected by a sensor.

  Regarding the abnormality detection of the NOx sensor provided on the downstream side of the selective catalytic reduction catalyst, the exhaust gas regulation is particularly strict, and it is not just a failure such as disconnection, but is accompanied by deterioration of the NOx sensor itself. Although it is required to correctly detect the reliability of the sensor output, since the exhaust gas reaching the NOx sensor is exhaust gas after passing through the selective catalytic reduction catalyst, the NOx sensor of the exhaust gas is used. The detected NOx concentration is in a state where NOx is well purified by the selective reduction catalyst, in a state where ammonia is slipping the selective reduction catalyst, or the NOx sensor itself is deteriorated, etc. Accordingly, it is difficult to determine whether the value is in an abnormal value state. Thus, the output value of the NOx sensor is the value of the selective catalytic reduction catalyst located upstream thereof. The sound from being reflected, thereby causing to lower the accuracy of the abnormality diagnosis of the NOx sensor.

  In order to eliminate such problems, a pre-catalyst NOx sensor and a post-catalyst NOx sensor are arranged on the upstream and downstream sides of the selective catalytic reduction catalyst, and when the abnormality is diagnosed, the addition of urea as a reducing agent is stopped. The post-catalyst NOx concentration is detected by the post-catalyst NOx sensor, the pre-catalyst NOx concentration upstream of the selective catalytic reduction catalyst is detected by the pre-catalyst NOx sensor, and the post-catalyst NOx concentration and the pre-catalyst NOx concentration are compared with each other. Thus, it has been proposed to determine the abnormality of the post-catalyst NOx sensor.

  Incidentally, when the addition of urea as the reducing agent is stopped, NOx is not reduced in the selective catalytic reduction catalyst, NOx passes through the selective catalytic reduction catalyst and reaches downstream, and NOx upstream of the selective catalytic reduction catalyst. Since the concentration and the NOx concentration downstream of the selective catalytic reduction catalyst are substantially equal, the NOx concentration detected by the post-catalyst NOx sensor deviates from the NOx concentration upstream of the selective catalytic reduction catalyst. It can be determined that the post-NOx sensor is abnormal.

  For example, Patent Document 1 shows a general technical level related to the abnormality diagnosis of the NOx sensor as described above.

JP 2008-133780 A

  However, as described above, when the addition of urea as a reducing agent is stopped at the time of abnormality diagnosis, an addition valve for adding urea as a reducing agent to a selective catalytic reduction catalyst inherently injects the reducing agent depending on the situation. Since the injection is stopped forcibly, it may be exposed to a high temperature, which is not a preferable measure.

  In view of such circumstances, the present invention provides an exhaust emission control device that can reliably detect an abnormality of a NOx sensor provided downstream of a selective catalytic reduction catalyst without stopping the addition of urea as a reducing agent. It is what.

The present invention is equipped with a selective reduction catalyst in the middle of an exhaust pipe, and urea water is added as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx, and at least downstream of the selective reduction catalyst. An exhaust purification device provided with a post-catalyst NOx sensor on the side,
In the temperature range where the post-catalyst NOx sensor operates and the activity of the selective catalytic reduction catalyst is low, the post-catalyst NOx concentration detected by the post-catalytic NOx sensor and the pre-catalyst provided upstream of the selective catalytic reduction catalyst Provided with abnormality determination means for determining abnormality of the post-catalyst NOx sensor by comparing with each other the pre-catalyst NOx concentration detected by the NOx sensor or the calculated value of engine exhaust NOx calculated based on the operating state of the engine The present invention relates to an exhaust emission control device characterized by the following.

  According to the above means, the following operation can be obtained.

  When the abnormality determination means recognizes that the post-catalyst NOx sensor is operating and the selective catalytic reduction catalyst is in a low temperature range, the post-catalyst NOx concentration detected by the post-catalyst NOx sensor and the selective reduction The pre-catalyst NOx concentration detected by the pre-catalyst NOx sensor provided upstream of the type catalyst or the engine exhaust NOx calculated value obtained based on the operating state of the engine is compared with each other and detected by the post-catalyst NOx sensor The post-catalyst NOx concentration, the pre-catalyst NOx concentration detected by the pre-catalyst NOx sensor provided upstream of the selective catalytic reduction catalyst, or the calculated engine exhaust NOx calculated based on the engine operating state If they are approximately equal, it is determined that the post-catalyst NOx sensor is normal, while the post-catalyst NOx concentration detected by the post-catalyst NOx sensor is When there is a deviation from the pre-catalyst NOx concentration detected by the pre-catalyst NOx sensor provided upstream of the selective catalytic reduction catalyst, or the calculated engine exhaust NOx calculated based on the operating state of the engine, the catalyst It is determined that the post-NOx sensor is abnormal.

  In the exhaust purification device, when warm-up control for increasing the temperature of the selective catalytic reduction catalyst is performed, the warm-up control is temporarily stopped when the abnormality determination unit determines abnormality of the post-catalyst NOx sensor. This is effective in preventing temperature increase of the selective catalytic reduction catalyst due to the warm-up control and reliably detecting abnormality of the post-catalyst NOx sensor.

  According to the exhaust emission control device of the present invention, it is possible to reliably detect an abnormality of the post-catalyst NOx sensor provided downstream of the selective catalytic reduction catalyst without stopping the addition of urea as a reducing agent. Can be played.

It is a general | schematic block diagram which shows the Example of this invention. It is a diagram which shows the relationship between the temperature and the ammonia adsorption amount by the selective reduction catalyst in the Example of this invention, and the relationship between the temperature and the purification rate by the selective reduction catalyst. It is a diagram which shows the operation start temperature of the post-catalyst NOx sensor and the operation start temperature of the selective catalytic reduction catalyst in the example of the present invention.

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

  1 to 3 show an embodiment of the present invention. In the illustrated diesel engine 1, a turbocharger 2 is provided, and air 4 guided from an air cleaner 3 is introduced into the turbocharger 2 via an intake pipe 5. The air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the air 4 is led from the intercooler 6 to an intake manifold (not shown) to be a diesel engine. 1 is introduced into each cylinder.

  The exhaust gas 7 discharged from each cylinder of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b is discharged outside the vehicle through the exhaust pipe 9. It is supposed to be.

  In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, a selective catalytic reduction catalyst 10 is mounted and mounted by a casing 11. The selective catalytic reduction catalyst 10 is, for example, a flow-through type honeycomb structure. And has the property of allowing NOx to react selectively with ammonia even in the presence of oxygen.

  Further, in the middle of the urea water supply line 15 extending from the urea water tank 20 in which the urea water 12 is stored, a supply pump 21 that pumps the urea water 12 in the urea water tank 20, and the pressure is pumped by the supply pump 21. A regulator 22 for adjusting the pressure of the urea water 12 and an injector 23 for injecting the urea water 12 whose pressure has been adjusted by the regulator 22 from the addition nozzle 16 into the exhaust pipe 9 upstream of the selective catalytic reduction catalyst 10 are provided. It is like that.

  On the other hand, the control device 24 outputs a drive command signal 21 a to the supply pump 21, outputs a pressure adjustment command signal 22 a to the regulator 22, and outputs a valve opening command signal 23 a to the injector 23. The addition amount of the urea water 12 is appropriately controlled by the valve opening operation of the injector 23, and the injection pressure required at the time of the addition can be appropriately obtained by driving the supply pump 21 and the operation of the regulator 22. It has become.

  In this embodiment, a pre-catalyst NOx sensor 30 and a post-catalyst NOx sensor 31 are disposed upstream and downstream of the selective catalytic reduction catalyst 10, and the pre-catalyst NOx concentration 30 a detected by the pre-catalyst NOx sensor 30. And the post-catalyst NOx concentration 31a detected by the post-catalyst NOx sensor 31 are input to the control device 24, and the control device 24 uses urea water based on the pre-catalyst NOx concentration 30a and the post-catalyst NOx concentration 31a. 12 is added to execute the addition of the required amount of urea water 12, and a temperature sensor 32 for detecting the temperature 32a of the selective catalytic reduction catalyst 10 is provided, and the temperature 32a detected by the temperature sensor 32 is set. Input is made to the control device 24.

  Here, in the selective catalytic reduction catalyst 10, as shown in FIG. 2, the lower the temperature, the higher the ammonia adsorption amount and the lower the purification rate. Also, in order to operate the post-catalyst NOx sensor 31, No water droplets are attached to the element, that is, a certain degree of high temperature (about 100 [° C.]) is required (see FIG. 3). When the temperature at which the catalyst 10 acts (about 180 to 200 ° C. as shown in FIG. 3) is reached, the after-catalyst NOx concentration 31a detected by the after-catalyst NOx sensor 31 of the exhaust gas 7 is the selective reduction catalyst. NOx is well purified or is in a state where ammonia is slipping the selective catalytic reduction catalyst, or the post-catalyst NOx sensor 31 itself shows an abnormal value due to deterioration or the like. State In the control device 24, the post-catalyst NOx sensor 31 operates and the selective catalytic reduction catalyst 10 has a low activity range (for example, 100 to 200 [° C.]). Range), the post-catalyst NOx concentration 31a detected by the post-catalyst NOx sensor 31 and the pre-catalyst NOx concentration 30a detected by the pre-catalyst NOx sensor 30 provided upstream of the selective catalytic reduction catalyst 10 By comparing each other, the abnormality of the post-catalyst NOx sensor 31 is determined, and the control device 24 is used as an abnormality determining means. The purification rate of the selective catalytic reduction catalyst 10 is higher when the exhaust gas 7 is at a lower flow rate than when the exhaust gas 7 is at a higher flow rate (see the phantom line in FIG. 2). The temperature range where the activity of 10 is low varies depending on the flow rate of the exhaust gas 7.

  Further, when the warm-up control for forcibly increasing the temperature of the selective catalytic reduction catalyst 10 is performed using a heater or the like (not shown), the abnormality of the post-catalyst NOx sensor 31 by the control device 24 as the abnormality determination means. At the time of determination, the warm-up control is temporarily stopped. When the warm-up control and the abnormality determination of the post-catalyst NOx sensor 31 are performed at the same time, the warm-up control is given priority instead of temporarily stopping the warm-up control each time. Then, the warm-up control may be stopped once every several times (for example, three to five times), and the abnormality determination of the post-catalyst NOx sensor 31 may be performed.

  Next, the operation of the above embodiment will be described.

  In the control device 24 as the abnormality determination means, based on the temperature 32a detected by the temperature sensor 32, the post-catalyst NOx sensor 31 operates and the temperature of the selective catalytic reduction catalyst 10 is low (for example, 100 to 200 [ Is detected by the post-catalyst NOx sensor 31 and the pre-catalyst NOx sensor 30 provided on the upstream side of the selective catalytic reduction catalyst 10. The pre-catalyst NOx concentration 30a is compared with each other.

  The post-catalyst NOx concentration 31a detected by the post-catalyst NOx sensor 31 and the pre-catalyst NOx concentration 30a detected by the pre-catalyst NOx sensor 30 provided upstream of the selective catalytic reduction catalyst 10 are substantially equal. Then, while the post-catalyst NOx sensor 31 is determined to be normal, the post-catalyst NOx concentration 31a detected by the post-catalyst NOx sensor 31 is the pre-catalyst provided upstream of the selective catalytic reduction catalyst 10. When the pre-catalyst NOx concentration 30a detected by the NOx sensor 30 is deviated, it is determined that the post-catalyst NOx sensor 31 is abnormal.

  In the control device 24, the rotational speed and load of the diesel engine 1 are exchanged with an engine control computer (ECU: Electronic Control Unit) (not shown). Since the amount of NOx generated is determined as the calculated value of engine exhaust NOx based on the current operating state of the diesel engine 1, the pre-catalyst NOx sensor 30 is omitted and the post-catalyst NOx sensor 31 detects it. By comparing the after-catalyst NOx concentration 31a with the calculated engine exhaust NOx calculated based on the operating state of the diesel engine 1, it is possible to determine whether the after-catalyst NOx sensor 31 is abnormal.

  Further, as shown in FIG. 1, in the case where a pre-catalyst NOx sensor 30 and a post-catalyst NOx sensor 31 are disposed on the upstream and downstream sides of the selective catalytic reduction catalyst 10, the calculated engine exhaust NOx value is obtained as the post-catalyst NOx sensor value. As reference values for the after-catalyst NOx concentration 31a detected by the NOx sensor 31 and the before-catalyst NOx concentration 30a detected by the before-catalyst NOx sensor 30 provided upstream of the selective catalytic reduction catalyst 10, respectively. Of course, it can be used.

  Further, when the warm-up control for forcibly increasing the temperature of the selective catalytic reduction catalyst 10 is performed using a heater or the like (not shown), the abnormality of the post-catalyst NOx sensor 31 by the control device 24 as the abnormality determination means. At the time of determination, since the warm-up control is temporarily stopped, the temperature increase of the selective catalytic reduction catalyst 10 due to the warm-up control is prevented, and it is possible to reliably detect an abnormality in the post-catalyst NOx sensor 31. Become.

  Thus, the abnormality of the post-catalyst NOx sensor 31 provided on the downstream side of the selective catalytic reduction catalyst 10 can be reliably detected without stopping the addition of urea as a reducing agent.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.

1 Diesel engine (engine)
7 Exhaust gas 9 Exhaust pipe 10 Selective reduction catalyst 12 Urea water 24 Control device (abnormality determination means)
30 NOx sensor before catalyst 30a NOx concentration before catalyst 31 NOx sensor after catalyst 31a NOx concentration after catalyst

Claims (2)

A selective reduction catalyst is provided in the middle of the exhaust pipe, and urea water is added as a reducing agent upstream of the selective reduction catalyst to reduce and purify NOx, and at the downstream of the selective reduction catalyst, An exhaust purification device provided with a NOx sensor,
In the temperature range where the post-catalyst NOx sensor operates and the activity of the selective catalytic reduction catalyst is low, the post-catalyst NOx concentration detected by the post-catalytic NOx sensor and the pre-catalyst provided upstream of the selective catalytic reduction catalyst Provided with abnormality determination means for determining abnormality of the post-catalyst NOx sensor by comparing with each other the pre-catalyst NOx concentration detected by the NOx sensor or the calculated value of engine exhaust NOx calculated based on the operating state of the engine An exhaust purification device characterized by the above.   The warm-up control is temporarily stopped when the abnormality determination of the post-catalyst NOx sensor is performed by the abnormality determination unit when the warm-up control for increasing the temperature of the selective catalytic reduction catalyst is performed. Exhaust purification device.

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