JP2019007458A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control device of an internal combustion engine which can maintain an exhaust emission control capacity.SOLUTION: When a temperature of an oxidation catalyst is not lower than an activation temperature Td (YES at step S4), and an exhaust emission temperature at an upstream side of a selective reduction-type catalyst is lower than a prescribed temperature which is higher than the activation temperature Td (YES at step S1), a urea water supply ECU injects urea water from a first injector 21 at an injection amount which is decided on the basis of an oxidation rate of the urea water at the oxidation catalyst 5 (step S6). The urea water supply ECU decides the injection amount so that the injection amount of the urea water from the first injector becomes large as the oxidation rate becomes high. When a NOx discharge amount between the oxidation catalyst 5 and the selective reduction-type catalyst 6 is larger than a NOx discharge amount at the internal combustion engine 2 side, the urea water supply ECU stops the injection of the urea water from the first injector.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Patent Document 1 provides a diesel exhaust gas for providing a nitrogen oxide reducing agent to the upstream side of the diesel particulate filter with an oxidation catalyst and the upstream side of the denitration catalyst layer, and switching the injection position of the reducing agent based on the exhaust gas temperature. A processing method is described.

  Further, the diesel exhaust gas treatment method described in Patent Document 1 injects a reducing agent into the upstream of the diesel particulate filter with an oxidation catalyst when the exhaust gas temperature is lower than a predetermined temperature, and denitrates when the exhaust gas temperature is higher than the predetermined temperature. A reducing agent is injected into the upstream of the catalyst layer.

  According to the diesel exhaust gas treatment method described in Patent Document 1, nitrogen oxides in diesel exhaust gas are efficiently decomposed and removed from the low temperature range to the high temperature range by switching the injection position of the reducing agent based on the exhaust gas temperature. can do.

JP 2004-270520 A

  However, in the diesel exhaust gas treatment method described in Patent Document 1, when the reducing agent is injected into the upstream of the diesel particulate filter with an oxidation catalyst, a part of the reducing agent is oxidized in the oxidation catalyst, and the reduction is performed. There was a problem that the agent was reduced. For this reason, in the diesel exhaust gas treatment method described in Patent Document 1, there is a possibility that the exhaust gas purification ability cannot be maintained.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can maintain the exhaust gas purification capability.

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with an oxidation catalyst and a selective reduction catalyst from the upstream side in an exhaust passage of the internal combustion engine, and is disposed upstream of the oxidation catalyst and reduces nitrogen oxides. A first injector that injects a reducing agent; a second injector that is disposed downstream of the oxidation catalyst and that injects the reducing agent upstream of the selective catalytic reduction catalyst; an injection amount of the first injector; A control unit that determines an injection amount of the two injectors, wherein the control unit has the oxidation catalyst at an activation temperature or higher and an exhaust gas temperature upstream of the selective reduction catalyst is higher than the activation temperature. When the temperature is lower than a predetermined temperature, the reducing agent is injected from the first injector at an injection amount determined based on an oxidation rate of the reducing agent in the oxidation catalyst.

  As described above, according to the present invention, the exhaust gas purification ability can be maintained.

FIG. 1 is a configuration diagram of a vehicle including an exhaust purification device for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining urea water injection control operation by the exhaust gas purification apparatus for an internal combustion engine according to one embodiment of the present invention. FIG. 3 is a timing chart for explaining the urea water injection control operation by the exhaust gas purification apparatus for an internal combustion engine according to one embodiment of the present invention.

  An exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is an exhaust gas purification apparatus for an internal combustion engine provided with an oxidation catalyst and a selective reduction catalyst from an upstream side in an exhaust passage of the internal combustion engine. A first injector that is disposed upstream and injects a reducing agent that reduces nitrogen oxides; a second injector that is disposed downstream of the oxidation catalyst and injects the reducing agent upstream of the selective catalytic reduction catalyst; and A control unit that determines an injection amount of the first injector and an injection amount of the second injector, and the control unit has an oxidation catalyst at an activation temperature or higher and an exhaust gas temperature upstream of the selective reduction catalyst is an activation temperature. When the temperature is lower than the predetermined temperature, the reducing agent is injected from the first injector at an injection amount determined based on the oxidation rate of the reducing agent in the oxidation catalyst. Thereby, the exhaust gas purification apparatus for an internal combustion engine according to the embodiment of the present invention can maintain the exhaust gas purification capacity.

An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 1, a vehicle 9 equipped with an exhaust purification device for an internal combustion engine according to an embodiment of the present invention includes an internal combustion engine 2, an engine ECU (Electronic Control Unit) 10, and an exhaust purification device 1. ing.

  The internal combustion engine 2 is configured by a four-cycle diesel engine that performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston reciprocates two cylinders. The internal combustion engine 2 may be a gasoline engine that performs lean combustion.

  The internal combustion engine 2 includes an intake pipe 11 that forms an intake passage 12 and an exhaust pipe 3 that forms an exhaust passage 4. Air that is taken into the internal combustion engine 2 passes through the intake passage 12. Exhaust gas discharged from the internal combustion engine 2 passes through the exhaust passage 4.

  The internal combustion engine 2 includes a turbocharger 13 in the exhaust passage 4, and the turbocharger 13 compresses the air in the intake passage 12 by the exhaust gas passing through the exhaust passage 4.

  The engine ECU 10 includes a computer unit including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, and an output port. The controlled object is electrically controlled. A program for causing the computer unit to function as the engine ECU 10 is stored in the ROM of the engine ECU 10 together with various control constants, various maps, and the like. Thus, in the engine ECU 10, the computer unit functions as the engine ECU 10 when the CPU executes the program stored in the ROM.

  The exhaust purification device 1 includes an oxidation catalyst 5 and a selective reduction catalyst 6, and the oxidation catalyst 5 and the selective reduction catalyst 6 are disposed on the exhaust passage 4 downstream of the turbocharger 13. The oxidation catalyst 5 is disposed on the upstream side of the selective reduction catalyst 6.

  The oxidation catalyst 5 has oxidation ability, and purifies the exhaust gas by efficiently oxidizing hydrocarbons and carbon monoxide in the exhaust gas. In the oxidation catalyst 5, hydrocarbons are oxidized to water vapor and carbon dioxide, and carbon monoxide is oxidized to carbon dioxide. In this embodiment, DOC (Diesel Oxidation Catalyst) is adopted as the oxidation catalyst 5.

  The selective catalytic reduction catalyst 6 is an SCR (Selective Catalytic Reduction) that reduces nitrogen oxides (hereinafter also referred to as NOx) in the exhaust gas. In this embodiment, an SDPF in which a DPF (Diesel Particulate Filter) that collects particulate matter is integrated with the SCR is employed as the selective reduction catalyst 6.

  In addition, the exhaust emission control device 1 includes a first injector 21 disposed on the upstream side of the oxidation catalyst 5, a second injector 22 disposed on the downstream side of the oxidation catalyst 5, an injection amount of the first injector 21, and a second injection amount. And a urea water supply ECU 20 as a control unit for determining the injection amount of the injector 22.

  The first injector 21 is configured to inject urea water as a reducing agent that reduces nitrogen oxides upstream of the selective catalytic reduction catalyst 6. The second injector 22 injects urea water as a reducing agent for reducing nitrogen oxides downstream of the oxidation catalyst 5, that is, upstream of the selective reduction catalyst 6. Urea water is a compound (ammonia precursor) that can be hydrolyzed to ammonia.

  Further, the exhaust purification device 1 includes an upstream NOx sensor 7 disposed on the upstream side of the selective catalytic reduction catalyst 6 and a downstream NOx sensor 8 disposed on the downstream side of the selective catalytic reduction catalyst 6.

  The upstream NOx sensor 7 and the downstream NOx sensor 8 detect the discharge amount of nitrogen oxide (hereinafter also referred to as NOx discharge amount), and transmit a detection signal to the urea water supply ECU 20 via the engine ECU 10.

  The NOx emission amount detected by the upstream NOx sensor 7 constitutes the first nitrogen oxide concentration in the present invention. The first nitrogen oxide concentration is not limited to the value detected by the upstream NOx sensor 7, and may be estimated by the urea water supply ECU 20 based on the operating state of the internal combustion engine 2 or the like.

  Further, the exhaust purification device 1 includes a NOx sensor (not shown) that detects the NOx emission amount between the oxidation catalyst 5 and the selective reduction catalyst 6 as the second nitrogen oxide concentration. The second nitrogen oxide concentration is not limited to the value detected by the NOx sensor, but may be estimated by the urea water supply ECU 20 based on the operating state of the internal combustion engine 2 or the like.

  The exhaust purification device 1 also includes a temperature sensor (not shown) that detects the exhaust gas temperature T1 around the first injector 21 and a temperature sensor (not shown) that detects the exhaust gas temperature T2 around the second injector 22. The detected exhaust gas temperatures T1 and T2 are transmitted to the urea water supply ECU 20. The exhaust gas temperatures T1 and T2 are not limited to being detected by a temperature sensor, but may be estimated by the urea water supply ECU 20 based on the operating state of the internal combustion engine 2 or the like.

  The urea water supply ECU 20 is configured by a computer unit having a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, and an output port. The control object is electrically controlled. That is, the urea water supply ECU 20 is composed of an ECU (Electronic Control Unit). The ROM of the urea water supply ECU 20 stores a program for causing the computer unit to function as the urea water supply ECU 20 along with various control constants and various maps. Thus, in the urea water supply ECU 20, the CPU functions as the urea water supply ECU 20 when the CPU executes the program stored in the ROM.

  Next, the flow of the urea water injection control operation executed by the urea water supply ECU 20 according to this embodiment will be described with reference to the flowchart shown in FIG.

  In FIG. 2, the urea water supply ECU 20 determines whether or not the exhaust gas temperature T2 is equal to or higher than the urea water injection possible temperature Ts2 of the second injector 22 (step S1). The urea water injection possible temperature Ts2 is a predetermined temperature higher than the activation temperature Td of the oxidation catalyst 5. The activation temperature Td is, for example, 180 ° C. The urea water injection possible temperature Ts2 is a temperature at which the urea water injected from the second injector 22 can be changed to ammonia, and is 200 ° C., for example.

  When the exhaust gas temperature T2 is lower than the urea water injection possible temperature Ts2 in step S1, the urea water supply ECU 20 determines whether or not the exhaust gas temperature T1 is equal to or higher than the urea water injection possible temperature Ts1 of the first injector 21. (Step S2).

  The urea water injection possible temperature Ts1 is a temperature at which the urea water injected from the first injector 21 can be changed to ammonia, and is 200 ° C., for example. The urea water jettable temperature Ts1 and the urea water jettable temperature Ts2 are the same temperature. When the exhaust gas temperature T1 is lower than the urea water injection possible temperature Ts1, the urea water supply ECU 20 ends the current operation.

  When the exhaust gas temperature T1 is equal to or higher than the urea water injection possible temperature Ts1 in step S2, the urea water supply ECU 20 starts injection of urea water from the first injector 21 (step S3). In step S3, the urea water supply ECU 20 sets the injection amount of urea water as the base urea water injection amount determined from the NOx emission amount determined from the operation region of the internal combustion engine 2. In step S3, the urea water supply ECU 20 keeps the second injector 22 non-injected.

  Next, the urea water supply ECU 20 determines whether or not the exhaust gas temperature T2 has reached the activation temperature Td of the oxidation catalyst 5 (denoted as the DOC activation temperature in the figure) (step S4). Here, the fact that the exhaust gas temperature T2 reaches the activation temperature Td of the oxidation catalyst 5 indicates that the exhaust gas temperature T2 has reached the activation temperature Td of the oxidation catalyst 5. If the exhaust gas temperature T2 does not reach the activation temperature Td in step S4, the urea water supply ECU 20 ends the current operation.

  When the exhaust gas temperature has reached the activation temperature in step S4, the urea water supply ECU 20 determines whether the NOx emission amount detected by the upstream NOx sensor 7 is larger than the NOx emission amount discharged from the internal combustion engine 2. Is determined (step S5).

  Here, in the oxidation catalyst 5 in the active state, as shown in the following reaction formulas 1 and 2, an oxidation reaction of ammonia occurs.

  4NH3 + 3O2 → 2N2 + 6H2O Reaction formula 1

  4NH3 + 5O2 → 4NO + 6H2O Reaction formula 2

  According to Reaction Formula 1, ammonia (NH 3) generated by thermal decomposition and hydrolysis from urea water is oxidized by air (O 2), thereby generating nitrogen (N 2) and water (H 2 O). That is, a part of the ammonia generated from the urea water disappears.

  On the other hand, according to reaction formula 2, ammonia (NH 3) generated by thermal decomposition and hydrolysis from urea water is oxidized by air (O 2), so that nitric oxide (NO) and water (H 2 O) are generated. Is done. That is, part of the ammonia generated from the urea water disappears and nitrogen monoxide, which is a nitrogen oxide, is generated. Moreover, these reaction formulas 1 and 2 have temperature dependence, and when the temperature is relatively low, the reaction formula 1 becomes the main reaction, and when the temperature is relatively high, the reaction formula becomes the main reaction.

  For this reason, when the oxidation catalyst 5 is at or above the activation temperature but at a relatively low temperature, the reaction formula 1 becomes the main reaction, and nitrogen oxide does not increase in the oxidation catalyst 5 and is detected by the upstream NOx sensor 7. The NOx emission amount is equal to or less than the NOx emission amount discharged from the internal combustion engine 2.

  On the other hand, when the temperature of the oxidation catalyst 5 becomes relatively high and the reaction formula 2 becomes the main reaction, nitrogen oxides are generated in the oxidation catalyst 5, so that the NOx emission amount detected by the upstream NOx sensor 7. Becomes larger than the NOx emission amount discharged from the internal combustion engine 2.

  Therefore, when the NOx emission amount detected by the upstream side NOx sensor 7 in step S5 is equal to or less than the NOx emission amount discharged from the internal combustion engine 2 (NO in step S5), the urea water supply ECU 20 has a reaction equation that becomes the main reaction. In order to compensate for ammonia that disappears due to 1, the amount of urea water injected from the first injector 21 is corrected to be increased (step S6), and the current operation ends.

In step S6, the urea water supply ECU 20 first determines the oxidation rate of ammonia in the oxidation catalyst 5 based on the exhaust gas temperature. This oxidation rate is a rate at which ammonia is decomposed into nitrogen and water by oxidation and disappears.
Further, the urea water supply ECU 20 determines the increase correction amount of the urea water based on this oxidation rate.
Accordingly, the urea water injection amount after the increase correction is an injection amount obtained by adding the correction amount based on the oxidation rate to the base urea water injection amount.

  In this way, when the oxidation catalyst 5 is at or above the activation temperature but at a relatively low temperature and the reaction formula 1 is the main reaction, the urea water is corrected to increase so as to offset the amount of ammonia that disappears due to oxidation. The For this reason, the exhaust gas purification capability can be maintained.

  On the other hand, when the NOx emission amount detected by the upstream NOx sensor 7 in step S5 is larger than the NOx emission amount discharged from the internal combustion engine 2 (YES in step S5), the nitrogen oxides are expressed by the reaction formula 2 which is the main reaction. In order to prevent it from being generated, the urea water supply ECU 20 stops the injection of urea water from the first injector 21 (step S7) and ends the current operation.

  As described above, when the oxidation catalyst 5 is at a temperature higher than the activation temperature and relatively high, and the reaction formula 2 is the main reaction, the injection of the urea water from the first injector 21 is stopped, so that the oxidation catalyst 5 Is prevented from generating nitrogen oxides. For this reason, the exhaust gas purification capability can be maintained.

  In step S1, if the exhaust gas temperature T2 is equal to or higher than the urea water injection possible temperature Ts2, the urea water supply ECU 20 starts injection of urea water from the second injector 22 (step S8) and ends the current operation. To do.

  Next, transition of the urea water injection position and the injection amount during the execution of the urea water injection control operation will be described with reference to the timing chart shown in FIG.

  In FIG. 3, the vertical axis indicates the urea water injection state from the second injector 22, the urea water injection state from the first injector 21, and the NOx emission amount detected by the upstream NOx sensor 7 in order from the top. And a comparison determination value flag between the NOx emission amount on the internal combustion engine 2 (E / G in the figure) side, the exhaust gas temperature T1 upstream of the oxidation catalyst 5, and the exhaust gas temperature T2 downstream of the oxidation catalyst 5 And the horizontal axis represents time.

  The injection and non-injection in the injection state of the first injector 21 and the second injector 22 are represented by ON and OFF. The comparison determination value flag is set to 1 when the NOx emission amount detected by the upstream NOx sensor 7 is larger than the NOx emission amount on the internal combustion engine 2 side.

  At the time t0 in the initial state, the internal combustion engine 2 is started and the exhaust gas temperatures T1 and T2 begin to rise. At this time t0, the first injector 21 and the second injector 22 are not injected (the injection amount is zero).

  Thereafter, since the exhaust gas temperature T1 reaches the urea water injection possible temperature Ts1 at time t1, the injection of urea water is started from the first injector 21, and the second injector 22 is kept non-injected.

  Thereby, the urea water injected from the first injector 21 is changed into ammonia by thermal decomposition and hydrolysis, and this ammonia is stored in the selective catalytic reduction catalyst 6. For this reason, NOx is reduced in the selective reduction catalyst 6.

  Thereafter, at time t2, the exhaust gas temperature T2 reaches the activation temperature Td of the oxidation catalyst 5, and the oxidation catalyst 5 becomes active. In this state, reaction formula 1 is the main reaction, and ammonia disappears due to oxidation in the oxidation catalyst 5. Therefore, urea water is injected from the first injector 21 at an injection amount determined based on the oxidation rate of ammonia in the oxidation catalyst 5. Further, the injection amount from the first injector is corrected to be increased so that the injection amount of urea water increases as the oxidation rate of ammonia increases. Therefore, the amount of ammonia increased and the amount of ammonia disappearing are balanced, and the former cancels out the latter.

  Thereafter, the comparison determination value flag changes from 0 to 1 at time t3, and the reaction formula 2 becomes the main reaction. Therefore, in order to prevent generation of nitrogen oxides due to oxidation of ammonia, The urea water injection is stopped.

  After that, since the comparison determination value flag has returned to 0 at time t4, the urea water injection from the second injector 22 is started. Moreover, the 1st injector 21 is maintained by non-injection. Note that when the injection of urea water from the first injector 21 is stopped at time t3, the comparison determination value flag quickly returns to 0, so that both the first injector 21 and the second injector 22 are non-injected. The period (period from time t3 to time t4) is an extremely short period.

  As described above, in the exhaust gas purification apparatus 1 of the present embodiment, the urea water supply ECU 20 is configured such that the oxidation catalyst 5 is equal to or higher than the activation temperature Td and the exhaust gas temperature T2 on the upstream side of the selective catalytic reduction catalyst 6 is the activation temperature Td. When the temperature is lower than the predetermined temperature, the urea water is injected from the first injector 21 at an injection amount determined based on the oxidation rate of ammonia in the oxidation catalyst 5.

  As a result, even if the selective catalytic reduction catalyst 6 is not heated up to a temperature at which the aqueous urea can be injected from the second injector 22, the aqueous urea is converted into ammonia in the oxidation catalyst 5 at a higher temperature than the selective catalytic reduction catalyst 6. The selective reduction catalyst 6 can purify NOx in the exhaust gas by this ammonia.

  In addition to this, since the amount of urea water injected from the first injector 21 is determined in consideration of the amount of ammonia that decreases due to oxidation in the oxidation catalyst 5, the amount of decrease in ammonia due to oxidation can be compensated. Exhaust gas purification capacity can be maintained.

  In this embodiment, the urea water supply ECU 20 determines the injection amount so that the urea water injection amount from the first injector 21 increases as the ammonia oxidation rate increases.

  Thereby, when the oxidation rate of ammonia increases, the injection amount of urea water is increased so as to cancel out the decrease in ammonia, so that the exhaust gas purification capability can be maintained.

  Further, in this embodiment, the urea water supply ECU 20 has a second amount between the oxidation catalyst 5 and the selective reduction catalyst 6 rather than the NOx emission amount as the first nitrogen oxide concentration upstream of the oxidation catalyst 5. When the NOx emission amount as the nitrogen oxide concentration is high, the urea water injection from the first injector 21 is stopped.

  Thereby, in the situation where nitrogen oxides are generated from the urea water injected from the first injector 21, the injection of urea water is stopped, so that the exhaust gas purification capability can be maintained.

  In this embodiment, ammonia or urea water which is a compound hydrolyzable into ammonia is used as the reducing agent.

  Thereby, ammonia and nitrogen oxide are reacted to generate nitrogen and water, so that the exhaust gas purification performance can be improved.

  While embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that changes may be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

DESCRIPTION OF SYMBOLS 1 Exhaust purification device 2 Internal combustion engine 4 Exhaust passage 5 Oxidation catalyst 6 Selective reduction type catalyst 20 Urea water supply ECU (control part)
21 1st injector 22 2nd injector

Claims (4)

An exhaust purification device for an internal combustion engine comprising an oxidation catalyst and a selective reduction catalyst from the upstream side in an exhaust passage of the internal combustion engine,
A first injector disposed upstream of the oxidation catalyst and injecting a reducing agent for reducing nitrogen oxides;
A second injector disposed downstream of the oxidation catalyst and injecting the reducing agent upstream of the selective catalytic reduction catalyst;
A controller that determines an injection amount of the first injector and an injection amount of the second injector;
The controller is
When the oxidation catalyst is at an activation temperature or higher and the exhaust gas temperature on the upstream side of the selective catalytic reduction catalyst is lower than a predetermined temperature higher than the activation temperature,
An exhaust emission control device for an internal combustion engine, wherein the reducing agent is injected from the first injector in an injection amount determined based on an oxidation rate of the reducing agent in the oxidation catalyst. The controller is
2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the injection amount is determined such that the amount of the reducing agent injected from the first injector increases as the oxidation rate increases. The controller is
When the second nitrogen oxide concentration between the oxidation catalyst and the selective catalytic reduction catalyst is higher than the first nitrogen oxide concentration upstream of the oxidation catalyst, the reducing agent from the first injector The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein the injection is stopped.   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the reducing agent is ammonia or a compound hydrolyzable to the ammonia.

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