JP2010138883A - Control device for exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute suitable elimination of NOx while attaining effective utilization of energy. <P>SOLUTION: This exhaust emission control system includes: an SCR catalyst 13 provided in an exhaust pipe 11 of an engine body E; a reducing agent storage part 20 for storing a solid reducing agent; an ammonia supply valve 31 for supplying a gaseous reducing agent generated from the solid reducing agent stored in the reducing agent storage part 20 to an upstream side of the SCR catalyst 13 in an exhaust passage; and a discharge port 15. The reducing agent storage part 20 is configured as a heating part for heating the solid reducing agent stored in the storage part 20 and uses exhaust heat in the exhaust pipe 11 as a heat source. An ECU 40 controls a heat supply amount by the exhaust heat from inside the exhaust pipe 11 to the reducing agent storage part 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an exhaust purification system, and in particular, suitably implements an exhaust purification system employing SCR (Selective Catalytic Reduction).

  In recent years, SCR has been developed as an exhaust purification system for purifying nitrogen oxide (NOx) in exhaust with a high purification rate in engines (particularly diesel engines) applied to automobiles, etc. Has reached.

As an SCR system, for example, an exhaust pipe connected to an engine body is provided with an SCR catalyst, and ammonia gas as a NOx reducing agent is supplied to the SCR catalyst (for example, Patent Documents). 1). In the system of Patent Document 1, a solid reducing agent such as solid urea is stored in a storage tank, and the solid reducing agent in the storage tank is heated by an electric heater to liquefy the solid reducing agent. Then, a liquid reducing agent is added to the upstream side of the SCR catalyst in the exhaust pipe. As a result, the reducing agent becomes a gas in the exhaust pipe, and the reducing agent in the gaseous state and NOx in the exhaust act. That is, NOx reduction reaction using ammonia as a reducing agent is performed on the SCR catalyst, and as a result, NOx in the exhaust is reduced and purified.
Japanese Patent Laid-Open No. 2002-4840

  By the way, when the NOx reducing agent is mounted in the system in a solid state, it is desirable to supply the NOx reducing agent into the exhaust pipe after changing the solid reducing agent into liquid or gas. At this time, as in Patent Document 1, when an electric heater is used when liquefying the solid reducing agent, an apparatus for supplying electric energy to the electric heater is required. For example, when an in-vehicle battery is used as the supply device, the battery voltage decreases as the electric power consumed by the electric heater is reduced. Therefore, it is necessary to drive the internal combustion engine to replenish the decrease, and as a result, the vehicle There is concern that the fuel economy will deteriorate.

  The present invention has been made to solve the above-described problems, and a main object of the present invention is to provide a control device for an exhaust gas purification system that can suitably perform NOx purification while effectively utilizing energy.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  In an exhaust gas purification system based on SCR, it is considered that a solid or liquid reducing agent is stored as a NOx reducing agent, and the solid or liquid reducing agent is supplied into the exhaust pipe after being gasified by heating or the like. It is done. Thereby, it is considered that the NOx reduction can be sufficiently performed by the selective reduction catalyst. Here, as a heat source for changing the solid or liquid reducing agent into a gas, the present inventors pay attention to the exhaust heat of the internal combustion engine, and control the heat supply amount to the solid or liquid reducing agent using the exhaust heat as a heat source. It was decided.

  That is, the exhaust purification system of the present invention includes a selective reduction catalyst provided in an exhaust passage of an internal combustion engine, a storage unit that stores a solid or liquid reducing agent, and a reduction of the solid or liquid stored in the storage unit. The present invention is applied to an exhaust gas purification system including a heating unit that heats the agent, and a reducing agent supply unit that supplies a gaseous reducing agent generated by heating by the heating unit to the upstream side of the selective reduction catalyst in the exhaust passage. The In the first aspect of the present invention, the heating unit includes a heat control unit that uses exhaust heat from the exhaust passage as a heat source and controls a heat supply amount by the exhaust heat from the heating unit to the storage unit. It is characterized by. According to this configuration, since the exhaust heat of the internal combustion engine is used as thermal energy for generating the gas reducing agent, compared with a case where the gas reducing agent is generated from a solid or liquid reducing agent using only an electric heater. , Energy consumption can be reduced. Moreover, since the amount of heat supplied to the reducing agent by the exhaust heat is adjusted, it is possible to suppress the excess or deficiency of the reducing agent supplied to the selective catalytic reduction catalyst. Therefore, NOx purification can be suitably performed while achieving effective use of energy.

  The amount of heat input to the solid or liquid reducing agent varies depending on the exhaust flow rate, and the amount of heat supplied to the reducing agent by the exhaust heat increases as the exhaust flow rate increases. Moreover, the exhaust heat used as the heat source of the heating unit varies depending on the engine operating state, the state of other exhaust purification devices disposed upstream of the SCR, and the like, for example, particulate matter (PM) in the exhaust ) In the exhaust passage, the exhaust temperature becomes excessively high (for example, 600 to 650 ° C.) during the regeneration process of the DPF, and the exhaust heat may increase. In such a case, it is necessary to suppress heat supply to the reducing agent due to exhaust heat.

  In view of this point, the invention according to claim 2 includes a flow rate adjusting means for adjusting an exhaust flow rate of an exhaust circulation portion that circulates exhaust heat that is a heat source of the heating portion in the exhaust passage, and the thermal control means. Controls the exhaust flow rate by the flow rate adjusting means as control of the heat supply amount. According to this configuration, the amount of heat supplied to the reducing agent can be adjusted by changing the exhaust gas flow rate, and as a result, the amount of gas reducing agent (for example, ammonia gas) generated can be suitably controlled.

  In addition, a bypass passage as an exhaust circulation part branched from the exhaust passage is provided as a flow control means, a flow control valve is provided in the bypass passage, and the opening degree of the flow control valve is adjusted to thereby adjust the bypass passage. The amount of heat supplied from the exhaust gas to the solid or liquid reducing agent may be controlled. By using the exhaust heat of the bypass passage provided in the exhaust passage, it is possible to suppress the stagnation of the exhaust flow in the exhaust passage when the exhaust flow rate is reduced by the flow rate control valve.

  As described above, for example, the exhaust temperature may be excessively high during the DPF regeneration process. According to a third aspect of the present invention, the storage section is provided with a cooling water passage for circulating the cooling water of the internal combustion engine, and the heat control means is configured to supply heat from the heating section to the storage section. It is determined that the supply is excessive, and when it is determined that the heat supply into the storage unit is excessive, the amount of heat supply into the storage unit is reduced by the cooling water flowing through the cooling water passage. According to this configuration, since the storage unit is cooled by the cooling water, the heat supply to the reducing agent due to the exhaust heat can be suppressed, and the generation amount of the gaseous reducing agent (such as ammonia gas) becomes excessive. Can be suppressed.

  Here, when the amount of heat supplied to the storage unit is controlled by the cooling water of the internal combustion engine, a means for adjusting the cooling water flow rate may be provided in the cooling water passage. In this way, the accuracy in controlling the heat supply amount can be increased. Moreover, it is desirable that the cooling water distributed to the storage unit is cooled by a radiator after being discharged from the internal combustion engine.

  For example, when starting an internal combustion engine or during idling, the exhaust temperature is low, and it is conceivable that exhaust heat sufficient to generate ammonia gas or the like from a solid or liquid reducing agent cannot be obtained. In view of this, the invention according to claim 4 is characterized in that the heating unit further includes a heating element that generates heat by electric energy as a heat source, and the heat control unit supplies heat from the heating unit to the storage unit. Is determined to be insufficient, and when it is determined that the heat supply into the storage unit is insufficient, heat is supplied from the heating element to the storage unit. According to this configuration, when the heat supply from the exhaust heat is insufficient, heat is supplied from the heating element to the solid or liquid reducing agent, so that the ammonia gas supplied to the selective catalytic reduction catalyst is prevented from being insufficient. can do. Further, since the heating element is used supplementarily when the heat supply due to the exhaust heat is insufficient, energy consumption can be suitably reduced as compared with the case where only the heating element (that is, the electric heater) is used.

  By the way, when exhaust heat is used for the change of the state of the reducing agent, it is conceivable that the exhaust temperature decreases as the heat energy moves. On the other hand, in order to promote the reaction in the exhaust purification catalyst, it is necessary to maintain the catalyst at the activation temperature.

  In view of this, the invention according to claim 5 is further provided in the exhaust passage with a filter for collecting particulate matter in the exhaust and an oxidation catalyst for promoting an oxidation reaction of nitrogen oxide in the exhaust. The heating unit uses exhaust heat on the downstream side of any one of the selective reduction catalyst, the filter, and the oxidation catalyst as a heat source. According to this configuration, since the exhaust heat on the downstream side of any one of the filter (DPF), the oxidation catalyst, and the SCR is used for the state change of the reducing agent, the purification function of the exhaust purification catalyst and the filter can be maintained. . In other words, by utilizing the exhaust heat downstream of the DPF, it is possible to avoid the reaction heat for DPF regeneration being transmitted to the storage unit, and as a result, it is possible to suppress adverse effects on the DPF regeneration. Can do. Further, by utilizing the exhaust heat downstream of the oxidation catalyst, the heat of oxidation reaction in the oxidation catalyst can be used for heating the reducing agent.

  According to a sixth aspect of the present invention, there is provided a gas storage unit that stores the reducing agent of the gas generated by heating of the heating unit between the storage unit and the reducing agent supply means, and the heat The control means controls the amount of heat supplied from the heating unit to the storage unit based on the pressure in the gas storage unit. According to the pressure in the gas storage unit, the amount of ammonia gas and the like released from the solid or liquid reducing agent can be detected quickly and accurately, and thus the amount of heat supplied to the reducing agent is suitably controlled. Can do.

(First embodiment)
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying an exhaust purification system according to the present invention will be described with reference to the drawings. The exhaust purification system of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as an SCR system. First, the configuration of this system will be described in detail with reference to FIG. FIG. 1 is a configuration diagram showing an outline of the SCR system according to the present embodiment.

  As shown in FIG. 1, this system has various actuators and various sensors for purifying exhaust as well as an ECU (electronic control unit) 40, etc., for exhaust gas exhausted by a diesel engine mounted on an automobile. Have built.

  Specifically, as an engine exhaust system configuration, an exhaust pipe 11 that forms an exhaust passage is connected to the engine body E, and a DPF (Diesel Particulate Filter) 12 and a selective catalytic reduction catalyst are connected to the exhaust pipe 11. (Hereinafter referred to as SCR catalyst) 13 is provided.

  The DPF 12 is a PM removal filter that collects PM (particulate matter) in the exhaust gas. The PM collected in the DPF 12 is burned and removed (regenerated) by post-injection after the main fuel injection in the diesel engine, and the DPF 12 can be used continuously.

The SCR catalyst 13 promotes a NOx reduction reaction (exhaust purification reaction). Specifically, for example,
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 12H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)
By promoting such a reaction, NOx in the exhaust gas is reduced and converted into N2 and H2O. This prevents NOx in the exhaust from being released into the atmosphere.

  Further, in the exhaust pipe 11, an exhaust sensor 16 incorporating a NOx detector (NOx sensor) and an exhaust temperature detector (exhaust temperature sensor) is provided downstream of the SCR catalyst 13. The exhaust sensor 16 detects the amount of NOx in the exhaust (NOx purification rate by the SCR catalyst 13) and the exhaust temperature on the downstream side of the SCR catalyst 13. In the exhaust pipe 11, an ammonia removal device 14 (for example, an oxidation catalyst) for removing ammonia (NH 3) in the exhaust gas is provided further downstream of the SCR catalyst 13. Further, an ammonia sensor or the like for detecting the amount of ammonia in the exhaust is provided further downstream of the SCR catalyst 13 as necessary.

  By the way, when NOx is reduced by the SCR catalyst 13, ammonia as a reducing agent is required. Therefore, in the present embodiment, a solid reducing agent is mounted as an ammonia generation source from the viewpoint of vehicle mountability and safety, and ammonia gas generated by heating the solid reducing agent is supplied to the SCR catalyst 13. Yes.

  Specifically, as shown in FIG. 1, a reducing agent storage unit 20 that stores a solid reducing agent is disposed adjacent to the exhaust pipe 11 further downstream of the ammonia removing device 14 in the exhaust pipe 11. Further, the reducing agent storage unit 20 is provided with a cooling water circulation pipe 17 as an engine cooling water passage so that the engine cooling water can circulate through the engine body E → the reducing agent storage unit 20 → the engine body E. ing. The cooling water circulation pipe 17 is provided with a cooling water metering valve 18 as an electromagnetic on-off valve, for example, upstream of the reducing agent storage unit 20. In the cooling water metering valve 18, the valve opening time or the opening degree can be adjusted by duty-controlling the energization amount, whereby the amount of engine cooling water passing through the reducing agent storage unit 20 is adjusted. The

  An engine-driven water pump WP is provided in the vicinity of the engine body E, and the engine coolant is circulated by driving the water pump WP. In addition, the upstream side of the reducing agent storage unit 20 and the downstream side of the radiator (not shown) are connected via the cooling water circulation pipe 17 so that the engine is cooled by the radiator after being discharged from the engine body E. It is desirable for water to pass through the reducing agent reservoir 20.

  FIG. 2 is a diagram illustrating details of the reducing agent storage unit 20. As shown in FIG. 2, the reducing agent storage unit 20 includes a heat transfer unit 21 that transfers heat in the exhaust pipe 11, a solid container 22 that stores the solid reducing agent, and an ammonia gas discharge port. And a discharge portion 23.

  The heat transfer section 21 conducts exhaust heat in the exhaust pipe 11 to the solid container 22 side, and is disposed in a state of penetrating the inside and outside of the exhaust pipe wall 11a. The heat transfer section 21 is made of a material (for example, stainless steel or carbon) that has high heat transfer and high corrosion resistance against ammonia. Inside the heat transfer section 21, a coolant circulation pipe 17 communicates with the outside of the exhaust pipe 11 along the direction in which the exhaust pipe 11 extends, so that the engine coolant can pass through the heat transfer section 21.

  The heat transfer section 21 is provided with heat receiving fins 21A and heat radiating fins 21B as a plurality of thin plate-like or rod-like protrusions. Specifically, heat receiving fins 21 </ b> A are provided in portions exposed to the exhaust in the exhaust pipe 11, and heat radiation fins 21 </ b> B are provided in portions exposed to the outside of the exhaust pipe 11. Thereby, the contact area of the heat-transfer part 21 and its periphery becomes large, and heat conduction is performed efficiently.

  The solid container 22 has a chamber 22A formed therein, in which the portion of the heat transfer section 21 exposed outside the exhaust pipe 11 (radiation fin 21B) is stored. Thereby, after the exhaust heat in the exhaust pipe 11 is received by the heat receiving fins 21A, it is released from the heat radiating fins 21B to the chamber 22A. The solid container 22 is provided with a temperature sensor 22B for detecting the temperature of the chamber 22A. In this chamber 22A, for example, a solid or granular solid reducing agent 25 is accommodated through an inlet (not shown) provided on the side surface of the solid container 22. Here, the solid reducing agent 25 is not particularly limited as long as it is a substance that releases ammonia gas by heating. For example, various ammine complexes (for example, CaCl2 · 8NH3, SrCl2 · 8NH3, MgCl2 · 6NH3), solid urea, Ammonium carbamate or the like is used.

  The discharge part 23 is provided, for example, in the upper part of the solid container 22 and is connected to one end of a gas pipe 26 in which a gas passage is formed. The other end of the gas pipe 26 is provided with a discharge port 15 for discharging ammonia gas, and the discharge port 15 is disposed in the exhaust pipe 11 between the DPF 12 and the SCR catalyst 13. That is, when the exhaust heat in the exhaust pipe 11 is released into the solid container 22 through the heat transfer section 21, vaporization or thermal decomposition of the solid reducing agent 25 accommodated in the solid container 22 occurs due to the heat. Ammonia gas is generated. The generated ammonia gas is discharged from the discharge portion 23 by using a pressure difference caused by the pressure increase due to gas generation, and then discharged to the upstream side of the SCR catalyst 13 through the gas pipe 26. The discharged ammonia gas is adsorbed by the SCR catalyst 13 and reacts with NOx in the exhaust gas in the SCR catalyst 13. That is, in the SCR catalyst 13, NOx is reduced and purified by the above reaction formulas (Formula 1) to (Formula 3) using ammonia as a reducing agent.

  In the gas pipe 26, a gas storage unit 27 that stores ammonia gas is disposed in the middle of the reducing agent storage unit 20 and the outlet 15. The gas storage unit 27 stores ammonia generated from the reducing agent storage unit 20 in a gaseous state. The gas storage unit 27 is provided with a pressure sensor 28 that detects an internal pressure and a temperature sensor 29 that detects a gas temperature. Further, an ammonia supply valve 31 as an electromagnetic on-off valve is provided between the gas storage unit 27 and the discharge port 15 in the gas pipe 26. The amount of ammonia discharged from the gas storage unit 27 into the exhaust pipe 11 is adjusted by the valve opening time or the opening degree of the ammonia supply valve 31.

  An oxidation catalyst is provided between the DPF 12 and the SCR catalyst 13 as needed to oxidize NO to NO2 and promote the reduction reaction in the SCR catalyst 13. In this case, a discharge port 15 is disposed between the oxidation catalyst and the SCR catalyst 13, and ammonia is discharged into the exhaust pipe 11 at the same position.

  Here, when exhaust gas is used to release ammonia gas from the solid reducing agent 25 in the solid container 22, for example, when the engine is started or during idling, the exhaust temperature is low and the solid reducing agent 25 It is conceivable that exhaust heat sufficient to release ammonia gas cannot be obtained. Therefore, in the present embodiment, for the purpose of assisting heating of the solid reducing agent 25, the reducing agent storage unit 20 is provided with a heater unit 24 that generates heat by electric energy. The heater unit 24 is built in, for example, a side wall of the solid container 22, and the amount of generated heat is adjusted by performing on / off switching control of energization to the heater unit 24.

  In the above system, the ECU 40 is a part that mainly performs control related to exhaust gas purification as an electronic control unit. The ECU 40 is composed mainly of a microcomputer 41 (hereinafter referred to as a microcomputer) composed of a CPU, a ROM, a RAM, and the like as well known, and executes various control programs stored in the ROM. That is, the microcomputer 41 of the ECU 40 operates the ammonia supply valve 31, the cooling water metering valve 18, the heater unit 24, and the like in a desired manner based on the detection values of the various sensors described above. Thus, various controls related to exhaust purification are performed.

  Specifically, the microcomputer 41 calculates the NOx amount on the downstream side of the SCR catalyst 13 based on the detection signal of the exhaust sensor 16 during engine operation, and based on the calculated NOx amount, the SCR in the exhaust pipe 11. The amount of ammonia discharged from the discharge port 15 is controlled upstream of the catalyst 13. In this case, a larger amount of NOx detected by the exhaust sensor 16 requires more ammonia. On the other hand, if ammonia is supplied in excess, excess ammonia that is not used in the NOx reduction reaction or is not adsorbed by the SCR catalyst 13 may be mixed with the exhaust gas and released into the atmosphere. Therefore, the microcomputer 41 controls the ammonia supply amount so that an appropriate amount of ammonia corresponding to the NOx amount detected by the exhaust sensor 16 is discharged into the exhaust pipe 11 from the discharge port 15.

  Regarding the control of the ammonia supply amount, the microcomputer 41 further controls the amount of ammonia gas generated from the solid reducing agent 25 by controlling the amount of heat supplied to the solid reducing agent 25 in the reducing agent storage unit 20. Thereby, the ammonia pressure PNH in the gas storage unit 27 is maintained within a predetermined range (for example, 2 to 2.5 atm). Further, the amount of ammonia gas released from the exhaust port 15 into the exhaust pipe 11 by setting the valve opening time or opening of the ammonia supply valve 31 based on the ammonia pressure PNH and the gas temperature TNH in the gas storage unit 27. To control. Thereby, an appropriate amount of ammonia is supplied to the SCR catalyst 13 with respect to the amount of NOx in the exhaust gas.

  Here, in generating ammonia gas from the solid reducing agent 25, this system basically uses the exhaust heat in the exhaust pipe 11, and generates ammonia gas from the solid reducing agent 25 by heating with the exhaust heat. is doing. However, depending on the exhaust temperature, the amount of heat supplied to the solid reducing agent 25 may be excessive or insufficient. Therefore, in this system, the heat supply amount to the solid reducing agent 25 is controlled by controlling the operation of the heater unit 24 and the cooling water metering valve 18. Specifically, the microcomputer 41 starts the circulation of the engine cooling water in the reducing agent storage unit 20 or the flow rate of the engine cooling water passing through the reducing agent storage unit 20 when the heat supply amount due to the exhaust heat is excessive. To increase. Thereby, the movement of exhaust heat from the exhaust pipe 11 to the reducing agent storage unit 20 is suppressed, and the amount of heat supplied to the solid reducing agent 25 is reduced. On the other hand, when the heat supply amount due to the exhaust heat is insufficient, energization to the heater unit 24 is started or the energization amount is increased. Thereby, the heating of the solid reducing agent 25 is assisted by the heater unit 24, and the amount of heat supplied to the solid reducing agent 25 is increased.

  Next, the heating process of the solid reducing agent 25 executed by the microcomputer 41 will be described using a flowchart. FIG. 3 is a flowchart showing a processing procedure for the heat treatment of the solid reducing agent 25. This process is executed at predetermined intervals by the microcomputer 41.

  In FIG. 3, first, in step S <b> 11, the detected value PNH of the ammonia pressure in the gas storage unit 27 detected by the pressure sensor 28 is a lower limit value Pmin (for example, 2) within a predetermined range as the pressure in the gas storage unit 27. Pressure) or more. When the detected value PNH of the ammonia pressure is less than the lower limit value Pmin, that is, when the heat supply amount to the solid reducing agent 25 is insufficient, the process proceeds to step S12, and the engine cooling water is sent from the engine body E and the reducing agent storage unit. Whether or not it is circulating between 20 is determined.

  When engine cooling water is circulating between the engine body and the reducing agent storage unit 20, that is, when the water pump WP is driven and the cooling water metering valve 18 is opened, go to step S13. Then, the flow rate of the engine cooling water in the cooling water circulation pipe 17 is reduced from the current time by reducing the duty ratio in the energization control of the cooling water metering valve 18. On the other hand, when the engine cooling water is not circulating, the process proceeds to step S14 where the energization of the heater unit 24 is turned on to supply heat from the heater unit 24 to the solid reducing agent 25. Thereby, the heating assistance by the heater part 24 is performed. That is, in this process, when increasing the amount of heat supplied to the solid reducing agent 25, first, the process of decreasing the flow rate of the engine cooling water is prioritized, and the gas is stored even if the flow rate of the engine cooling water is zero. When the ammonia pressure PNH in the part 27 is lower than the lower limit value Pmin, the heater part 24 is operated.

  If the detected value PNH of the ammonia pressure is equal to or greater than the lower limit value Pmin, an affirmative determination is made in step S11, the process proceeds to step S15, and the heater unit 24 is turned off by energizing the heater unit 24. The heat supply to the reducing agent 25 is stopped.

  In subsequent step S16, it is determined whether or not the detected value PNH of the ammonia pressure exceeds an upper limit value Pmax (for example, 2.5 atmospheres) within a predetermined range as the pressure in the gas storage unit 27. If the detected value PNH of the ammonia pressure is equal to or lower than the upper limit value Pmax, the detected value PNH is within the set range, so this routine is terminated as it is to maintain the state.

  On the other hand, when the detected value PNH of the ammonia pressure is larger than the upper limit value Pmax, that is, when the heat supply amount to the solid reducing agent 25 is excessive, the process proceeds to step S17, and the duty ratio in the energization control of the cooling water metering valve 18 Is increased, the flow rate of the engine cooling water in the cooling water circulation pipe 17 is increased from the present time.

  In addition, although it was set as the structure which makes the flow volume of engine cooling water variable according to the detected value PNH of ammonia pressure, it is good also as a structure which switches ON / OFF of circulation of engine cooling water according to the detected value PNH of ammonia pressure. Further, the flow rate of the engine cooling water is decreased when the detected value PNH of the ammonia pressure becomes less than the lower limit value Pmin. However, the detected value PNH of the ammonia pressure is, for example, between the lower limit value Pmin and the upper limit value Pmax. It is good also as a structure which decreases the flow volume of engine cooling water when it falls below the predetermined value. Similarly, when the flow rate of the engine coolant is increased, instead of increasing the flow rate of the engine coolant when the detected value PNH of the ammonia pressure exceeds the upper limit value Pmax, the detected value PNH of the ammonia pressure is, for example, the lower limit value Pmin. The flow rate of the engine cooling water may be increased when a predetermined value defined between the upper limit value Pmax and the upper limit value Pmax is exceeded. Furthermore, it is good also as a structure which changes the flow volume of engine cooling water continuously according to the detected value PNH of ammonia pressure.

  According to the embodiment described above, the following excellent effects can be obtained.

  When generating ammonia gas as a gaseous reducing agent from the solid reducing agent 25, exhaust heat from the engine body E is used as thermal energy for generating ammonia, so that energy consumption can be reduced. In addition, since the amount of exhaust heat supplied to the solid reducing agent 25 is adjusted, the amount of ammonia gas in the gas storage unit 27 can be set to an appropriate amount, and as a result, excess of the reducing agent supplied to the SCR catalyst 13 can be maintained. The shortage can be suppressed. Therefore, NOx purification can be suitably performed while achieving effective use of energy.

  Since the cooling water circulation pipe 17 is provided through the reducing agent storage unit 20 so that the engine cooling water passes through the reducing agent storage unit 20, the exhaust temperature is high, and heat is supplied from the exhaust heat to the reducing agent storage unit 20. When the amount is excessive, the reducing agent reservoir 20 can be cooled. Thereby, the heat supply to the solid reducing agent 25 by the exhaust heat can be suppressed, and as a result, the generation amount of ammonia can be suppressed from becoming excessive.

  Further, since the cooling water metering valve 18 is provided in the cooling water circulation pipe 17 as means for adjusting the cooling water flow rate in the cooling water circulation pipe 17, the inside of the cooling water circulation pipe 17 is controlled by energization control of the cooling water metering valve 18. The cooling water flow rate can be adjusted. As a result, the accuracy in controlling the amount of heat supplied to the solid reducing agent 25 can be increased.

  Since the heater unit 24 that generates heat by electric energy is provided and heat is supplied from the heater unit 24 when the heat supply from the exhaust pipe 11 to the solid reducing agent 25 is insufficient, for example, at the time of engine start, idle operation, etc. In this case, even when the exhaust gas temperature is low and sufficient exhaust heat to generate ammonia cannot be obtained, the heat supply amount to the solid reducing agent 25 can be secured by the heating assistance by the heater unit 24. . Thereby, it can suppress that the ammonia supplied to the SCR catalyst 13 runs short.

  By providing the reducing agent storage unit 20 on the downstream side of the DPF 12, the SCR catalyst 13 and the ammonia removing device 14, the solid reducing agent 25 is heated using the exhaust heat on the downstream side of the DPF 12, the SCR catalyst 13 and the ammonia removing device 14 as a heat source. Since it was set as the structure, it can suppress that the function fall of DPF12, the SCR catalyst 13, and the ammonia removal apparatus 14 resulting from the fall of the exhaust temperature accompanying utilization of the exhaust heat in the reducing agent storage part 20 arises. That is, by using the exhaust heat downstream of the DPF 12, it is possible to avoid the amount of heat required for the DPF regeneration being consumed due to the thermal decomposition of the solid reducing agent 25 or the like. Thereby, it is possible to suppress an adverse effect on the DPF regeneration. Further, by using the exhaust heat downstream of the SCR catalyst 13, the reaction temperature necessary for promoting the NOx purification reaction in the SCR catalyst 13 can be ensured. Thereby, it can suppress that a bad influence is exerted on NOx purification. In addition, by using the exhaust heat downstream of the ammonia removing device 14, a reaction temperature necessary for promoting the oxidation reaction of ammonia can be ensured. Thereby, it is possible to suppress the occurrence of ammonia slip.

  A gas storage unit 27 for storing ammonia gas is provided between the reducing agent storage unit 20 and the discharge port 15, and is based on the exhaust heat based on the detected value PNH of the ammonia pressure in the gas storage unit 27 detected by the pressure sensor 28. Since the heat supply amount to the solid reducing agent 25 is controlled, the amount of ammonia released from the solid reducing agent 25 toward the discharge port 15 can be detected quickly and accurately. The amount of heat supplied can be controlled suitably.

  Further, the ammonia gas released from the reducing agent storage unit 20 is temporarily stored in the gas storage unit 27 before being discharged into the exhaust pipe 11, that is, the gas storage unit 27 functions as a buffer. Therefore, it is possible to avoid a situation in which the ammonia gas discharged to the shortage is short, and to stably supply ammonia to the SCR catalyst 13.

  In increasing the amount of heat supplied to the solid reducing agent 25, priority is given to the process of reducing the flow rate of the engine cooling water, and detection of the ammonia pressure in the gas storage unit 27 even if the flow rate of the engine cooling water is made zero. Since the heater unit 24 is operated when the value PNH is lower than the lower limit value Pmin, the opportunity for heating the solid reducing agent 25 by the heater unit 24 can be reduced as much as possible, which is suitable for reducing energy consumption. is there.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. In the first embodiment, the reducing agent storage unit 20 is disposed in the exhaust pipe 11 provided with the SCR catalyst 13 and the like. However, in this embodiment, the SCR catalyst 13 and the like are provided. The exhaust pipe 11 is provided with a bypass pipe branched from the exhaust pipe 11 as means for adjusting the exhaust flow rate to the reducing agent storage unit 20. And the reducing agent storage part 20 is arrange | positioned in the bypass piping.

  FIG. 4 is a configuration diagram showing an outline of the SCR system in the present embodiment. This figure is a modification of part of FIG. In FIG. 4, the same components as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted. Although illustration is omitted, the configurations of the DPF 12, the gas storage unit 27, and the ammonia supply valve 31 are the same as those in FIG.

  As shown in FIG. 4, the exhaust pipe 11 is provided with a bypass pipe 51 branched from the exhaust pipe 11 on the downstream side of the ammonia removing device 14. A reducing agent storage unit 20 is attached to the bypass pipe 51, and an exhaust metering valve 52 as an electromagnetic on-off valve is provided on the upstream side of the reducing agent storage unit 20. In addition, the reducing agent storage part 20 of this embodiment differs from the reducing agent storage part 20 of the said embodiment in the point that the cooling water circulation piping 17 as a passage of engine cooling water is not provided in the inside.

  The exhaust metering valve 52 is adjusted in duty by duty control based on a drive signal from the ECU 40, so that its valve opening time or opening is adjusted. That is, according to the exhaust metering valve 52, the exhaust gas flow rate in the bypass pipe 51 is controlled, and as a result, the heat supply amount to the reducing agent storage unit 20 is controlled.

  Next, the heating process of the solid reducing agent 25 executed by the microcomputer 41 will be described using a flowchart. FIG. 5 is a flowchart showing a processing procedure for heating the solid reducing agent 25. This process is executed at predetermined intervals by the microcomputer 41.

  5, first, in step S21, it is determined whether or not the detected value PNH of the ammonia pressure in the gas storage unit 27 detected by the pressure sensor 28 is equal to or higher than the lower limit value Pmin. When the detected value PNH of the ammonia pressure is lower than the lower limit value Pmin, the process proceeds to step S22, and the duty ratio of the energization control of the exhaust metering valve 52 is set to the maximum value in a predetermined range, that is, bypass. It is determined whether the exhaust flow rate in the pipe 51 is maximum.

  If the duty ratio of the energization control of the exhaust metering valve 52 is not set to the maximum value and the exhaust flow rate in the bypass pipe 51 is not the maximum, the process proceeds to step S23, and the duty ratio is set to increase the exhaust flow rate. Enlarge. On the other hand, when the exhaust gas flow rate is maximum, the process proceeds to step S24, the energization of the heater unit 24 is turned on, and the heat supply from the heater unit 24 to the solid reducing agent 25 is performed. That is, in this process, when increasing the amount of heat supplied to the solid reducing agent 25, first, the process of increasing the exhaust flow rate in the bypass pipe 51 is prioritized to maximize the exhaust flow rate in the bypass pipe 51. However, when the detected value PNH of the ammonia pressure in the gas storage unit 27 is lower than the lower limit value Pmin, the heater unit 24 performs heating assistance.

  Further, when the detected value PNH of the ammonia pressure in the gas storage unit 27 is equal to or higher than the lower limit value Pmin, an affirmative determination is made in step S21, the process proceeds to step S25, and the energization to the heater unit 24 is turned off. Then, the heat supply from the heater unit 24 to the solid reducing agent 25 is stopped. In the subsequent step S26, it is determined whether or not the detected value PNH of the ammonia pressure exceeds the upper limit value Pmax. If the detected value PNH of the ammonia pressure is equal to or lower than the upper limit value Pmax, the detected value PNH is within the set range. Therefore, this routine is terminated as it is to maintain the state.

  On the other hand, when the detected value PNH of the ammonia pressure is larger than the upper limit value Pmax, the process proceeds to step S27, and the duty ratio of the energization control of the exhaust metering valve 52 is decreased in order to decrease the exhaust flow rate in the bypass pipe 51. Thereby, the exhaust heat supplied to the reducing agent storage unit 20 is reduced, and the amount of ammonia generated is reduced.

  According to the embodiment described above, the following excellent effects can be obtained.

  Since the bypass pipe 52 and the exhaust metering valve 52 are provided for the exhaust pipe 11 and the reducing agent storage unit 20 is disposed adjacent to the bypass pipe 52, the exhaust metering valve 52 changes the exhaust flow rate in the bypass pipe 52. Thus, the amount of heat supplied to the solid reducing agent 25 can be adjusted, and as a result, the amount of ammonia produced from the solid reducing agent 25 can be suitably controlled. In particular, for example, when the exhaust temperature becomes excessively high (for example, 600 to 650 ° C.) during the regeneration process of the DPF 12, for example, it is considered that the heat supply to the solid reducing agent 25 becomes excessive. Since the flow rate can be set to zero or in the vicinity thereof, it is possible to avoid the solid reducing agent 25 from being heated excessively by the excessively high temperature exhaust. Therefore, compared with the case where heat supply is suppressed by engine cooling water as in the above embodiment, the same suppression can be performed.

  Since the heat supply amount to the solid reducing agent 25 is controlled by increasing / decreasing the exhaust flow rate of the bypass pipe 51, when the exhaust flow rate to the reducing agent storage unit 20 is reduced by the exhaust metering valve 52, the exhaust control amount is adjusted. Compared with the configuration in which the quantity valve 52 and the reducing agent storage unit 20 are provided in the exhaust pipe 11, the exhaust from the engine body E can be discharged smoothly from the exhaust pipe 11.

  In increasing the amount of heat supplied to the solid reducing agent 25, priority is given to the process of increasing the exhaust flow rate in the bypass pipe 51, and even if the exhaust flow rate is maximized, the ammonia pressure in the gas storage unit 27 is detected. Since the heater unit 24 is operated when the value PNH is lower than the lower limit value Pmin, the opportunity for heating the solid reducing agent 25 by the heater unit 24 can be reduced as much as possible, which is suitable for reducing energy consumption. is there.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  The higher the detected value PNH of the ammonia pressure in the gas storage unit 27 detected by the pressure sensor 28, the larger the amount of ammonia gas generated from the solid reducing agent 25, and the lower the detected value PNH, the more generated from the solid reducing agent 25. Since it is determined that the amount of ammonia gas is small, the heat supply amount to the solid reducing agent 25 is controlled based on the detected value PNH of the ammonia pressure, but this is changed and detected by the temperature sensor 22B. The heat supply amount to the solid reducing agent 25 may be controlled based on the temperature in the solid container 22. Specifically, the amount of ammonia gas generated from the solid reducing agent 25 increases as the temperature in the solid container 22 increases, and the amount of ammonia gas generated from the solid reducing agent 25 decreases as the temperature in the solid container 22 decreases. Therefore, when the temperature in the solid container 22 is higher than the set temperature, the amount of engine cooling water in the cooling water circulation pipe 17 is controlled by the energization control of the cooling water metering valve 18 or the exhaust metering valve 52. Or the exhaust flow rate in the bypass pipe 51 is decreased. On the other hand, when the temperature in the solid container 22 is lower than the set temperature, the engine cooling water amount in the cooling water circulation pipe 17 is decreased or the exhaust gas flow rate in the bypass pipe 51 is increased. At this time, the heater unit 24 may be energized to supply heat from the heater unit 24 to the solid reducing agent 25.

  Alternatively, the heat supply amount to the solid reducing agent 25 may be controlled based on the exhaust temperature detected by the exhaust sensor 16 instead of the detected value PNH of the ammonia pressure. Specifically, the higher the exhaust temperature, the more exhaust heat is generated, so the amount of ammonia gas generated from the solid reducing agent 25 is larger. The lower the exhaust temperature, the less exhaust heat is generated, so the amount of ammonia gas generated from the solid reducing agent 25 is small. Therefore, when the exhaust temperature is higher than the temperature range appropriate for releasing ammonia from the solid reducing agent 25, the energization control of the cooling water metering valve 18 or the exhaust metering valve 52 is performed. The amount of engine cooling water in the cooling water circulation pipe 17 is increased, or the exhaust flow rate in the bypass pipe 51 is decreased. On the other hand, when the exhaust temperature is lower than the above temperature range, the amount of engine cooling water in the cooling water circulation pipe 17 is decreased or the exhaust flow rate in the bypass pipe 51 is increased. At this time, the heater unit 24 may be energized to supply heat from the heater unit 24 to the solid reducing agent 25.

  In the first embodiment, the reducing agent storage unit 20 is disposed adjacent to the exhaust pipe 11, and in the second embodiment, the reducing agent storage unit 20 is disposed adjacent to the bypass pipe 51. As long as exhaust heat can be supplied to the reducing agent storage unit 20, the position of the reducing agent storage unit 20 with respect to the exhaust pipe 11 or the bypass pipe 51 is not particularly limited. For example, the exhaust pipe 11 and the reducing agent storage unit 20 may be arranged separately from each other, and the exhaust heat in the exhaust pipe 11 may be transmitted to the reducing agent storage unit 20 using air as a medium.

  In the second embodiment, the bypass pipe 51 is provided on the downstream side of the ammonia removing device 14 and the reducing agent storage unit 20 is disposed adjacent to the bypass pipe 51. A bypass pipe 51 may be provided between the ammonia removing device 14, between the DPF 12 and the SCR catalyst 13, or upstream of the DPF 12.

  In the second embodiment, the exhaust pipe passing through the bypass pipe 51 is returned to the exhaust pipe 11 by connecting the downstream side of the bypass pipe 51 branched from the exhaust pipe 11 to the exhaust pipe 11. The exhaust gas passing through the bypass pipe 51 may be directly released into the atmosphere.

  In the reducing agent storage unit 20, the heat transfer unit 21 penetrates the inside and outside of the exhaust pipe wall 11 a and the exhaust heat is transmitted to the solid reducing agent 25 in the solid container 22 through the heat transfer unit 21. However, it is also possible to change this, arrange the solid container 22 directly on the outer surface of the exhaust pipe wall 11a, and transmit the exhaust heat to the solid reducing agent 25 in the solid container 22 through the exhaust pipe wall 11a. Good. Moreover, in the heat-transfer part 21, it is good also as a structure which does not provide at least any one of the heat receiving fin 21A and the radiation fin 21B.

  -It is good also as a structure which heats the solid reducing agent 25 with the heater part 24 in the predetermined period after engine starting operation. When starting the engine, it is conceivable that the exhaust gas temperature is low and sufficient exhaust heat is not supplied to generate ammonia gas from the solid reducing agent 25. Therefore, in a predetermined period after the engine start operation, the solid reductant 25 is heated by the heater unit 24, so that it is possible to suppress the shortage of the ammonia supply amount when starting the engine. Here, the predetermined period after the engine start operation is determined, for example, as an elapsed time since the ignition is turned on, or a period until the engine rotational speed becomes equal to or higher than the predetermined rotational speed.

  In the case where a substance that undergoes sublimation at a stretch by heating, such as solid urea or ammonium carbamate, is used as the solid reducing agent 25, a reducing agent supply port may be provided in the solid container 22. In this case, the amount of the solid reducing agent 25 introduced from the reducing agent supply port is adjusted in accordance with the amount of NOx in the exhaust gas, and the temperature in the solid container 22 becomes an optimum temperature for sublimating the solid reducing agent 25. It is preferable that the amount of heat supplied to the reducing agent storage unit 20 is controlled to be as follows.

  -When the reducing agent storage part 20 is provided in the bypass piping 51, it is good also as a structure which makes the reducing agent storage part 20 penetrate the cooling water circulation piping 17. As shown in FIG. In this way, it is possible to control the amount of heat supplied to the reducing agent storage unit 20 by the exhaust flow rate, the engine coolant flow rate, and the heater unit 24.

  -Although it was set as the structure which assists a heating with the heater part 24, it is good also as a structure which does not install the heater part 24. FIG. For example, the heater unit 24 is not installed when the generation start temperature of ammonia gas from the solid reducing agent 25 by vaporization or thermal decomposition is lower than the minimum value that can be taken by the exhaust gas temperature. Alternatively, when the ammonia gas from the solid reducing agent 25 is stored in the gas storage unit 27 when the exhaust gas is hot and the ammonia gas stored in the gas storage unit 27 is supplied into the exhaust pipe 11 when the exhaust gas temperature is low, the heater is used. The part 24 is not installed.

  The heater unit 24 generates heat by electric energy. However, the heater unit 24 is not limited to this as long as it is a heating element, and may be configured to generate heat by a chemical reaction, gas, or the like.

  In the first embodiment, the reducing agent storage unit 20 is arranged on the downstream side of the ammonia removing device 14, but this is changed so that the SCR catalyst 13 and the ammonia removing device 14 and the DPF 12 It is good also as a structure which provides the reducing agent storage part 20 between the SCR catalysts 13 or the upstream of DPF12.

  When the ammonia pressure PNH is higher than the upper limit value Pmax, the engine cooling water reduces the amount of heat supplied from the heat transfer unit 21 to the solid reducing agent 25. However, instead of using engine cooling water, heat transfer You may provide the cooling device for reducing the heat supply amount from the part 21 to the solid reducing agent 25 separately.

  -Although the solid reducing agent 25 was used as the reducing agent stored in the reducing agent storage part 20, this may be changed and liquid reducing agents, such as urea aqueous solution, may be used, for example. That is, the liquid reducing agent in the reducing agent storage unit 20 is changed to gas by storing the reducing agent in a liquid state in the reducing agent storage unit 20 and controlling the heat supply amount by the exhaust heat. The gaseous reducing agent is temporarily stored in the gas storage unit 27 via the gas pipe 26, and the ammonia gas in the gas storage unit 27 is discharged into the exhaust pipe 11 from the discharge port 15.

  In addition to practical application as an SCR system for on-board diesel engines, practical application as an SCR system for other engines such as gasoline engines (spark ignition engines) is possible.

The block diagram which shows the outline | summary of an SCR system. The block diagram which shows the outline | summary of a reducing agent storage part. The flowchart which shows the process sequence of the heat processing of a solid reducing agent. The block diagram which shows the outline | summary of the SCR system in 2nd Embodiment. The flowchart which shows the process sequence of the heat processing of the solid reducing agent in 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe, 13 ... SCR catalyst (selective reduction type catalyst), 15 ... Discharge port (reducing agent supply means), 17 ... Cooling water circulation piping, 18 ... Cooling water metering valve, 20 ... Reducing agent storage part (storage part) , Heating unit), 20A ... heat receiving fins, 20B ... radiation fins, 22 ... container for solid, 22B ... temperature sensor, 23 ... discharge unit, 24 ... heater unit (heating element), 25 ... solid reducing agent, 27 ... gas storage Part (gas storage part), 28 ... pressure sensor, 31 ... ammonia supply valve (reducing agent supply means), 40 ... ECU, 41 ... microcomputer, 51 ... bypass pipe (flow rate adjusting means, exhaust circulation part), 52 ... exhaust control Quantity valve (flow rate adjusting means).

Claims (6)

A selective reduction catalyst provided in an exhaust passage of an internal combustion engine; a storage unit that stores a solid or liquid reducing agent; a heating unit that heats a solid or liquid reducing agent stored in the storage unit; and the heating Applied to an exhaust gas purification system comprising a reducing agent supply means for supplying a gaseous reducing agent generated by heating by a part upstream of the selective reduction catalyst in the exhaust passage,
The heating unit uses exhaust heat from the exhaust passage as a heat source,
A control device for an exhaust purification system, comprising a heat control means for controlling a heat supply amount by exhaust heat from the heating unit to the storage unit. A flow rate adjusting means for adjusting an exhaust flow rate of an exhaust circulation part that circulates exhaust heat that is a heat source of the heating part in the exhaust passage;
2. The exhaust purification system control device according to claim 1, wherein the heat control unit controls an exhaust flow rate of the flow rate adjusting unit as control of the heat supply amount. The storage section is provided with a cooling water passage for circulating the cooling water of the internal combustion engine,
The heat control means is configured to determine that the heat supply from the heating unit into the storage unit is excessive, and to determine that the heat supply into the storage unit is excessive, The control device of the exhaust gas purification system according to claim 1 or 2, further comprising means for reducing a heat supply amount into the storage unit by circulating cooling water. The heating unit further includes a heating element that generates heat by electric energy as a heat source,
The heat control means is configured to determine that the heat supply from the heating unit into the storage unit is insufficient, and from the heating element when it is determined that the heat supply into the storage unit is insufficient. The control device of the exhaust gas purification system according to any one of claims 1 to 3, further comprising: means for supplying heat to the storage unit. The exhaust passage further includes a filter that collects particulate matter in the exhaust and an oxidation catalyst that promotes an oxidation reaction of nitrogen oxides in the exhaust,
The exhaust purification system control device according to any one of claims 1 to 4, wherein the heating unit uses exhaust heat in the downstream side of any of the selective reduction catalyst, the filter, and the oxidation catalyst as a heat source. . Between the storage unit and the reducing agent supply means, a gas storage unit for storing the gaseous reducing agent generated by heating the heating unit is provided,
The exhaust heat purification system control device according to any one of claims 1 to 5, wherein the heat control unit controls a heat supply amount from the heating unit to the storage unit based on a pressure in the gas storage unit.

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