JP5388286B2 - Exhaust purification device and control method thereof - Google Patents

Description

The present invention relates to an exhaust purification device and a control method thereof, and more particularly to an exhaust purification device that purifies NO _x (nitrogen oxide) discharged from an internal combustion engine using a reducing agent and an SCR (Selective Catalytic Reduction) catalyst and a control method thereof.

Conventionally, NO _x or the like is contained in exhaust gas of an internal combustion engine such as an automobile. As an exhaust purification device for purifying NO _x , an SCR catalyst (NO _x selective reduction catalyst) is disposed in the exhaust pipe of the internal combustion engine, and urea water as a reducing agent is disposed in the exhaust pipe upstream of the SCR catalyst. there is a urea SCR system for purifying NO _X was added (urea solution).

In the urea SCR system, urea water is stored in a reducing agent tank, and the urea water is supplied to a reducing agent addition valve via a reducing agent supply pipe or the like by a pump or the like. The reducing agent addition valve is fixed to the exhaust pipe upstream of the SCR catalyst, and urea water as a reducing agent is added from the reducing agent addition valve into the exhaust pipe. The added urea water is hydrolyzed by exhaust heat to become NH ₃ (ammonia) and reaches the SCR catalyst, and NH ₃ and NO _x react with each other on the SCR catalyst to reduce and purify NO _x .

  The urea water used in the urea SCR system is frozen at, for example, −11 ° C., and the volume increases with freezing. For this reason, in a low temperature environment, if the inside of the reducing agent supply pipe or the like is filled with urea water after the internal combustion engine is stopped, the reducing agent supply pipe or the like is caused by an increase in volume accompanying freezing of the urea water. There is a risk of damage. Further, if the urea water is frozen inside the reducing agent supply pipe or the like when the internal combustion engine is restarted, there is a risk that the start of the reducing agent addition promptly may be hindered due to clogging of the piping or the like by the urea water.

  Therefore, after the internal combustion engine is stopped, the pump for supplying the reducing agent is driven in the sucked back state, so that the air is supplied to the reducing agent supply pipe via the intake valve and the reducing agent addition valve connected to the reducing agent supply pipe. A technique has been proposed in which urea water is sucked back into the reducing agent tank and recovered while introducing the water (see, for example, Patent Document 1).

JP 2008-101564 A (the whole sentence, all figures)

In the case of the above-mentioned patent document 1 and the like, after the internal combustion engine is stopped, the reducing agent supply pipe is almost free of urea water and is filled with air. Therefore, when the SCR system is made to function again with the restart of the internal combustion engine, it is necessary to release air outside the reducing agent supply pipe and fill the reducing agent supply pipe with urea water. However, in the technique described in Patent Document 1, the air in the reducing agent supply pipe does not completely escape and remains as bubbles, and the accuracy of pressure control in the reducing agent supply pipe is reduced, thereby controlling the injection of urea water. accuracy is lowered, it may be impossible to sufficiently purify the nO _X in the exhaust gas.

  The present invention effectively discharges gas components existing in a reducing agent supply path such as a reducing agent supply pipe and a reducing agent addition valve to the outside of the reducing agent supply path in an exhaust gas purification apparatus such as the urea SCR system described above. Accordingly, an object of the present invention is to provide an exhaust emission control device and a control method therefor in which pressure control in the reducing agent supply path is accurately performed and injection control of the reducing agent can be performed accurately.

According to the present invention, there is provided an exhaust purification device that purifies exhaust gas from an internal combustion engine using an SCR catalyst and a reducing agent, the reducing agent tank storing the reducing agent, and adding the reducing agent upstream of the SCR catalyst. And a reducing agent supply pump for supplying the reducing agent from the reducing agent tank to the reducing agent addition valve via a reducing agent supply path. e Bei negative pressure generating means for by sucking the gas component in the supply path to release to the outside of the reducing agent supply path, the negative pressure generating means is an aspirator is operated by compressed air supplied by the air compressor is that there is provided an exhaust purification device, characterized in, it is possible to solve the problems described above (claim 1).

In constituting the exhaust gas purifying apparatus of the present invention, the negative pressure generating means, not preferred that it is connected to the reducing agent supply path through the solenoid valve.

Further, when configuring the exhaust emission control device of the present invention, a reducing agent supply path between the reducing agent tank and the reducing agent supply pump is provided with a three-way solenoid valve, and at least a part of the compressed air supplied by the air compressor is reduced. it is not preferable that is configured to be supplied to the agent supply path.

Another aspect of the present invention provides a reducing agent tank for storing the reducing agent, a reducing agent addition valve for adding the reducing agent upstream of the SCR catalyst, and a reducing agent supply path from the reducing agent tank to the reducing agent addition valve. And a reducing agent supply pump for supplying the reducing agent to the exhaust gas purification apparatus, wherein the reducing agent supply pump supplies the reducing agent to the reducing agent supply path while the internal combustion engine is started. by actuating the generating means, Ru control method der exhaust gas purifier, characterized in that by sucking gas component of the reducing agent supply path is released to the outside of the reducing agent supply path.

  According to the exhaust emission control device of the first aspect, the reducing agent is supplied by the suction force generated by the negative pressure generating means while the reducing agent is supplied to the reducing agent supply path by the reducing agent supply pump or after being supplied. By sucking the gas component in the path, the gas component is released out of the reducing agent supply path. As a result, air bubbles are prevented from remaining inside the reducing agent supply pipe and the like, enabling accurate pressure control in the reducing agent supply path, and accurately reducing the amount of reducing agent required for exhaust purification. It can be added to the exhaust pipe.

Further, according to the exhaust emission control device of claim 1 , for example, in a vehicle generally equipped with an air compressor such as a bus or a truck, the gaseous component is released out of the reducing agent supply path only by connecting an aspirator. Can be made. Further, since the air compressor may have a small output, even a vehicle not equipped with an air compressor can be easily added at low cost.

Further, according to the exhaust gas purification apparatus of the second aspect , it is possible to prevent the reducing agent from leaking out from the gas discharge passage or the like by closing the electromagnetic valve after releasing the gas component from the reducing agent supply path. The waste of energy for driving the reducing agent supply pump can be prevented. Further, since the path between the negative pressure generating means and the reducing agent supply path can be arbitrarily interrupted, the operation start timing of the negative pressure generating means and the suction start timing of the gas component from the reducing agent supply path are separated. be able to. For example, even when an air compressor mounted on a bus or truck for purposes other than the present invention is used, a gas component is sucked from the reducing agent supply path at any time without hindering the original purpose. can do.

Further, according to the exhaust purification device of the third aspect , when the internal combustion engine is stopped, the reducing agent in the reducing agent supply path can be efficiently recovered to the reducing agent tank by using the pressure of the compressed air. In addition, problems associated with freezing of the reducing agent can also be solved. Furthermore, there is no need to open the reducing agent addition valve to introduce air into the reducing agent supply path, thus preventing foreign materials such as unburned fuel and soot from entering the reducing agent supply path from the exhaust pipe. it can.

Further, according to the control method for the exhaust gas purification apparatus according to claim 4 , the negative pressure generating means is operated while supplying the reducing agent into the reducing agent supply path, whereby the effect of the positive pressure generated by the reducing agent supply pump is achieved. The effects of the suction force generated by the negative pressure generating means are overlapped, and the gas component can be efficiently discharged out of the reducing agent supply path.

It is a figure for demonstrating the structural example of the exhaust gas purification apparatus which concerns on 1st Embodiment. It is a flowchart for demonstrating the control method of the exhaust gas purification apparatus which concerns on 1st Embodiment. It is a figure for demonstrating the structural example of the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a flowchart for demonstrating the control method of the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a flowchart for demonstrating the control method of the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating the state of the reducing agent supply apparatus at the time of filling with a reducing agent. It is a figure for demonstrating the state of the reducing agent supply apparatus at the time of reducing agent addition control. It is a figure for demonstrating the state of the reducing agent supply apparatus at the time of cooling of the reducing agent addition valve during reducing agent addition control. It is a figure for demonstrating the state of the reducing agent supply apparatus at the time of reducing agent purge control. It is a figure for demonstrating the state of the reducing agent supply apparatus at the time of cooling of the reducing agent addition valve after the internal combustion engine stops.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying an exhaust emission control device and an exhaust emission control device control method according to the present invention will be described with reference to the drawings. Control method for an exhaust purification device and exhaust purification device of the embodiment is to purify the exhaust gas NO _X in an internal combustion engine using _the NO _X selective reducing catalyst, and is constructed as a urea SCR system. In the drawings, the same reference numerals denote the same members, and descriptions thereof are omitted as appropriate. In addition, embodiment described below shows one form of this invention, This invention is not limited, It can change arbitrarily within the scope of the present invention.

[First Embodiment]
1. Outline of Exhaust Purification Device FIG. 1 shows an outline of the overall configuration of the exhaust purification device 10 of the present embodiment. The exhaust gas purification device 10 is a device that purifies NO _{x in} exhaust gas discharged from an internal combustion engine 11 such as a diesel engine mounted on a vehicle. The exhaust purification device 10 is constructed from various sensors arranged in the exhaust system of the internal combustion engine 11, an SCR catalyst 14, an ammonia slip catalyst 15, a reducing agent adding device 20, a negative pressure generating device 30, a control device 40, and the like. . Further, the control device 40 can communicate with a control device (not shown, hereinafter referred to as “ECU: Engine Control Unit”) for controlling the operating state of the internal combustion engine 11, and fuel. Information relating to the control of the internal combustion engine 11 such as the injection amount, the injection timing, the rotational speed of the internal combustion engine, and the coolant temperature of the internal combustion engine can be read.

  The exhaust system of the internal combustion engine 11 is configured such that an exhaust pipe 12 is connected to the internal combustion engine 11 and an SCR catalyst 14 is disposed in the exhaust pipe 11. A reducing agent addition valve 21 for adding urea water as a reducing agent into the exhaust pipe 11 is fixed between the internal combustion engine 11 and the SCR catalyst 14. Further, an ammonia slip catalyst 15 is disposed downstream of the SCR catalyst 14.

An exhaust temperature sensor 13 is provided on the upstream side of the SCR catalyst 14, and a NO _x sensor 16 is provided on the downstream side. These sensors detect temperature information and NO _x concentration information inside the exhaust pipe 12 and transmit them to the control device 40, the ECU, and the like. Although a detailed description of the ECU is omitted here, a control device for a general internal combustion engine used in an automobile or the like may be used.

SCR catalyst 14, together with the exhaust pipe 12 to the added urea water harmless by reducing NO _X in the exhaust gas by contacting the NO _X in the exhaust gas in the SCR catalyst 14 to N ₂ (nitrogen) or the like NO _x selective reduction catalyst to be converted, and known ones are used as appropriate.

The ammonia slip catalyst 15 is a catalyst for oxidizing surplus NH ₃ that has passed through the SCR catalyst 14 without being used for the reduction reaction of NO _x , and a known one is used as appropriate.

  In the present embodiment, the control of the reducing agent adding device 20 and the negative pressure generating device 30 is performed by the common control device 40, but can also be controlled by using different control devices. Moreover, it is also possible to perform it by ECU as one function in ECU.

2. Reducing agent addition device The reducing agent addition device 20 is a device for adding and supplying urea water as a reducing agent stored in the reducing agent tank 25 into the exhaust pipe 12 via the reducing agent addition valve 21 and the like. The reducing agent addition apparatus 20 includes a reducing agent addition valve 21, a reducing agent supply pipe 22, a reducing agent supply pump 23, a reducing agent feeding pipe 24, a reducing agent tank 25, a reducing agent discharge pipe 26, an orifice 27, and a reducing agent addition valve. It comprises a cooling device 28, a reducing agent pressure sensor 29, and the like. Each actuator in the reducing agent adding device 20 is controlled by the control device 40.

  The reducing agent addition valve 21 has substantially the same configuration as an existing fuel injection valve (injector). Since a known configuration can be adopted as appropriate, the configuration will be briefly described here. The reducing agent addition valve 21 is configured as an electromagnetic on-off valve including a drive unit composed of an electromagnetic solenoid or the like and a valve body unit having a needle for opening and closing the addition hole at the tip. The valve is opened or closed based on the drive signal. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and the addition hole at the tip is opened by the needle movement, and urea water is added.

  Further, the reducing agent addition valve 21 includes an electromagnetic solenoid, a resin cover, a nozzle plate, and the like, which are weak against heat as compared with other components, and the heat-resistant temperature thereof is, for example, 160 for an electromagnetic solenoid or a nozzle plate. It is about 120 ° C. with a resin cover. Therefore, the reducing agent addition valve cooling device 28 is provided in the exhaust purification device 10 of the present embodiment. The reducing agent addition valve cooling device 28 cools the reducing agent addition valve 21 using a part of the cooling water of the internal combustion engine 11. The cooling water is circulated between the reducing agent addition valve 21 and the internal combustion engine 11 through the flow rate adjusting valve 63 and the like, and the circulating flow rate is determined based on the operating state of the internal combustion engine 11, the exhaust gas temperature, the reducing agent. It is appropriately adjusted by the control device 40 according to the temperature or the like.

  Next, the configuration of a reducing agent supply system for supplying urea water to the reducing agent addition valve 21 will be described. To the reducing agent addition valve 21, urea water as a reducing agent is sequentially supplied from the reducing agent tank 25. The reducing agent tank 25 is constituted by an airtight container with a liquid supply cap, and urea solution having a predetermined concentration is stored therein. Further, when the pressure in the reducing agent tank 25 exceeds a predetermined value, a pressure adjusting valve 37 is provided for adjusting the pressure in the tank by releasing the gas in the tank to the outside of the tank. As a countermeasure against freezing of urea water in the reducing agent tank 25, a heater may be attached to the reducing agent tank 25, or a heat insulating material such as a heat insulating sheet may be provided around the tank.

  A reducing agent supply pump 23 is connected to the reducing agent tank 25 via a reducing agent feeding pipe 24. One end of a reducing agent supply pipe 22 is connected to the reducing agent supply pump 23, and the other end of the reducing agent supply pipe 22 is connected to a reducing agent addition valve 21. The reducing agent supply pump 23 is an electric pump that is rotationally driven by a drive signal from the control device 40, and its output is a reducing agent pressure sensor 29 so that the pressure of the urea water in the reducing agent supply pipe 22 becomes a predetermined value. Feedback control is performed based on the value of.

  When the reducing agent supply pump 23 is driven to rotate with the start of the reducing agent addition device 20, urea water is pumped from the reducing agent tank 25 and supplied to the reducing agent addition valve 21 through the reducing agent supply pipe 22. One end of a reducing agent discharge pipe 26 is connected to the reducing agent supply pipe 22 via an orifice 27, and the other end of the reducing agent discharge pipe 26 is connected to a reducing agent tank 25. Thereby, when the pressure in the reducing agent supply path such as the reducing agent addition valve 21 and the reducing agent supply pipe 22 rises excessively, a part of the urea water in the reducing agent supply pipe 22 is reduced in the reducing agent tank. Returned to 25.

  Further, the reducing agent supply pump 23 used in the exhaust purification apparatus 10 of the present embodiment is configured such that the rotation direction can be reversed in the forward and reverse directions, and the reducing agent supply pump 23 rotates in the reverse direction when the internal combustion engine 11 is stopped. Thus, the urea water in the reducing agent supply path is collected in the reducing agent tank 25.

In the reducing agent addition device 20, during operation of the internal combustion engine 11, urea water in the reducing agent tank 25 is supplied to the reducing agent addition valve 21 through the reducing agent supply pipe 22 by driving the reducing agent supply pump 23, and the reducing agent is supplied. Urea water is added into the exhaust pipe 11 by the addition valve 21. Then, the urea water while produced NH ₃ is hydrolyzed in the exhaust pipe 11, is supplied to the SCR catalyst 14 with exhaust gas, the exhaust gas is purified by the reduction reaction of the NO _X is performed in the SCR catalyst 14 .

3. Negative Pressure Generating Device The negative pressure generating device 30 is a device for releasing gas components present in the reducing agent supply path such as the reducing agent supply pipe 22 and the reducing agent addition valve 21 to the outside of the exhaust purification device 10. The negative pressure generating device 30 provided in the exhaust purification device 10 of the present embodiment includes an aspirator 31, an air compressor 32, a solenoid valve 33, a compressed air supply pipe 34, a gas suction pipe 35, and a gas discharge pipe 36, and is controlled. Controlled by device 40.

  The aspirator 31 has a driving fluid supply port 71, a driving fluid discharge port 73, a suction port 75, and a throttle unit 77. The driving fluid supply port 71 is connected to the air compressor 32 via the compressed air supply pipe 34, and the driving fluid discharge port 73 is connected to the reducing agent tank 25 via the gas discharge pipe 36. The suction port 75 is connected to the reducing agent supply path of the reducing agent addition device 20 via the gas suction pipe 35. An electromagnetic valve 33 is provided in the middle of the gas suction pipe 35.

  In the aspirator 31, the compressed air supplied by the air compressor 32 flows into the inside from the driving fluid supply port 71, passes through the throttle portion 77, and is discharged from the driving fluid discharge port 73. In the throttle portion 77, the cross-sectional area is smaller than the cross-sectional area of the driving fluid supply port 71, and when compressed air passes, the flow velocity increases, so the pressure is lower than the surroundings due to the venturi effect. . A suction port 75 communicates with the throttle portion 77, and external fluid flows into the low pressure portion via the suction port 75, so that the vicinity of the suction port 75 becomes negative pressure. Therefore, when the aspirator 31 is operated, the gas component in the reducing agent supply path is sucked into the suction port 75 and is discharged from the gas discharge pipe 36 to the reducing agent tank 25 together with the compressed air. The gaseous components in the compressed air and the reducing agent supply path are released into the reducing agent tank 25 and then released outside the tank via the pressure adjusting valve 37 of the reducing agent tank 25.

  In a general reducing agent supply device mounted on a vehicle, the volume of the reducing agent supply path or the like is about 20 cc, the cutoff pressure of a general piston type air compressor is about 10 atm, and further reduction Considering the time required for the compressed air to be filled in the agent supply path and the compressed air supply pipe, the air compressor 32 for operating the aspirator 31 has an output of about 10 W and a discharge amount of 10 L / min. A small-sized compressor may be used. As such an air compressor, a known one can be used as appropriate.

  If the output of the air compressor 32 is larger than that described above, the object can be achieved. Therefore, for example, an air compressor mounted on a bus or truck for purposes other than the present invention can be used. However, when using an existing air compressor mounted on a vehicle, a valve device or the like for adjusting the flow rate of the compressed air is provided.

  The electromagnetic valve 33 is controlled by the control device 40 so as to be opened when a gas component is extracted from the reducing agent supply path, and is controlled so as to be closed in other cases. As a result, it is possible to prevent the urea water from leaking through the gas suction pipe 35 after releasing the gas component from the reducing agent supply path, and it is possible to prevent waste of driving energy of the reducing agent supply pump 23. Further, since the negative pressure generator 30 and the reducing agent supply path can be arbitrarily opened and closed, the operation start timing of the air compressor 32 and the suction start timing of the gas component from the reducing agent supply path can be separated. As a result, for example, even when using an air compressor mounted on a bus or truck for purposes other than the present invention, the gas from the reducing agent supply path at any time without impairing its original purpose. It is possible to adjust the starting time of sucking components.

4). Control Device The control device 40 mainly performs control related to exhaust gas purification as an electronic control unit in the exhaust gas purification device. The control device 40 includes a known microcomputer (not shown), a storage device (not shown), and the like, and the reducing agent adding device 20 and the negative pressure generating device in a desired manner based on detection values of various sensors. By operating 30, various controls relating to exhaust purification are performed. Specifically, an appropriate amount of urea water is added into the exhaust pipe 11 at an appropriate time by controlling the energization time of the reducing agent addition valve 21 and the driving amount of the reducing agent supply pump 23 as will be described later. Supply. In addition, by controlling the energization timing of the electromagnetic valve 33, the drive amount of the air compressor 32, and the like, gas components are prevented from remaining in the reducing agent supply path when filling the reducing agent supply path with urea water. .

5. Next, an example of a control flow of the exhaust purification device 10 performed by the control device 40 will be described with reference to FIG.

  First, when the internal combustion engine is started and the execution of this control flow is started, the driving of the air compressor 32 is started in step S01 after START. Next, in step S02, the electromagnetic valve 33 is controlled to be turned on and opened, and in step S03, the timer T is reset and the timer T starts counting. Further, in step S04, driving to rotate the reducing agent supply pump 23 in the forward direction is started, and filling of the urea water in the reducing agent tank 25 into the reducing agent supply path is started. As a result, the gas component in the reducing agent supply path is released to the reducing agent tank 25 via the aspirator 31 and the like by the positive pressure generated by the pumping of urea water by the reducing agent supply pump 23 and the suction force generated by the aspirator 31. start.

  Next, in step S05, it is determined whether or not the value of the timer T is equal to or greater than a preset value T0. T0 is the time required for sufficiently releasing the gas component in the reducing agent supply path based on the discharge flow rate of the reducing agent supply pump 23 and the capacity of the reducing agent supply path. Pre-filled. If the value of timer T is less than T0, step S05 is repeated.

  When the value of the timer T is equal to or greater than T0, that is, when it is estimated that the gas component in the reducing agent supply path has been released, the process proceeds to step S06. If suction from the reducing agent supply path is performed for a time longer than T0, the low-pressure urea water returns to the reducing agent tank 25 more than necessary via the aspirator 31. There is no impact. However, when the pressure in the reducing agent supply path is maintained at a predetermined pressure, the driving energy of the reducing agent supply pump 23 becomes large.

When the gas component is released from the reducing agent supply path as described above, the electromagnetic valve 33 and the air compressor 32 are turned off in step S06. In this state, the reducing agent supply path is filled only with urea water maintained at a constant pressure by the orifice 27. Then, it progresses to step S07 and urea water addition control is started and this control flow is complete | finished. During the urea water addition control, the reducing agent addition valve 21 is controlled in accordance with the operating state of the internal combustion engine, etc., to purify NO _x in the exhaust gas, and urea water is added into the exhaust pipe.

  In the present embodiment, the example in which the driving of the reducing agent supply pump 23 and the suction of the gas component by the aspirator 31 are started simultaneously has been described. However, even when the driving of the reducing agent supply pump 23 is started first and the suction by the aspirator 31 is started from a state in which the urea water is supplied to some extent in the reducing agent supply path, the urea water and the gas component ( Due to the difference in specific gravity with air), it is possible to mainly release the gas component out of the reducing agent supply path.

  Moreover, in this Embodiment, the method of controlling a negative pressure generator based on the elapsed time after starting the reducing agent supply pump 23 and the air compressor 32 was shown. Besides this, for example, based on the driving current of the reducing agent supply pump 23 or the pressure transition in the reducing agent supply pipe, the filling rate of the urea water in the reducing agent supply path or the residual degree of the gas component is estimated to generate negative pressure. The device 30 can also be controlled. Furthermore, the negative pressure generator 30 can be controlled in consideration of information obtained from the ECU. In addition, various negative pressure generating means such as a known vacuum pump can be used even if it is other than an aspirator.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with a focus on differences from the first embodiment. A description of the same contents as in the first embodiment will be omitted.

1. FIG. 3 shows an outline of the overall configuration of the exhaust gas purification apparatus 10A according to the present embodiment. In the reducing agent addition apparatus 20A of the present embodiment, a compressed air supply three-way solenoid valve 51, a reducing agent supply three-way solenoid valve 52, and a cooling compressed air supply pipe 53 are further added to the reducing agent addition apparatus of the first embodiment. A reducing agent purge compressed air supply pipe 54, a pressure regulator 61, a reducing agent addition valve cooling device 65, and the like are added or changed. Each actuator and the like are controlled by the control device 40A as in the first embodiment.

  In the exhaust purification apparatus 10A of the present embodiment, when the internal combustion engine is stopped, the urea water remaining in the reducing agent supply path can be recovered using the negative pressure generator 30A instead of the reducing agent supply pump 23A. It is configured. Further, the exhaust purification apparatus 10A of the present embodiment is configured such that the reducing agent addition valve 21 can be cooled using compressed air supplied from the air compressor 32 that constitutes the negative pressure generating apparatus 30A.

  The compressed air supply three-way solenoid valve 51 is provided in a compressed air supply pipe 34 between the aspirator 31 and the air compressor 32, and one end side is connected so that compressed air from the air compressor 32 can flow in. The other end of the compressed air supply three-way solenoid valve 51 is connected to the aspirator 31 so that compressed air can be introduced, and the other end is cooled by the reducing agent addition valve cooling device 65 provided in the reducing agent addition valve 21. The compressed air can be introduced through the compressed air supply pipe 53 for use. The three-way solenoid valve 51 for supplying compressed air is controlled based on a control signal from the control device 40A, and the flow of compressed air flows from the air compressor 32 to the aspirator 31 or from the air compressor 32 to the reducing agent addition valve cooling device 65. It can be switched appropriately.

  Further, the compressed air supply pipe 34 from the compressed air supply three-way solenoid valve 51 to the aspirator 31 branches in the middle, and a part of the compressed air supplied from the air compressor 32 is compressed air supply pipe for reducing agent purge. It is also sent to the reducing agent supply three-way solenoid valve 52 via 54. The compressed air supplied to the reducing agent supply three-way solenoid valve 52 is used when recovering urea water.

  The reducing agent supply three-way solenoid valve 52 is provided in the middle of the reducing agent feeding pipe 24, and one end is connected to the reducing agent tank 25 and the other end is connected to the reducing agent supply pump 23A via a pipe. . The remaining end is connected to a compressed air supply pipe 34 between the compressed air supply three-way solenoid valve 51 and the aspirator 31 via a reducing agent purge compressed air supply pipe 54. Thereby, based on the control signal from the control device 40A, the urea water in the reducing agent tank 25 is led to the reducing agent supply pump 23, and the compressed air is led from the air compressor 32 to the reducing agent supply pump 23. Are appropriately switched.

  Further, the reducing agent addition valve 21 in the present embodiment has a plurality of radiating fins on the outer peripheral surface, and the exhaust heat transmitted to the reducing agent addition valve 21 directly or indirectly through the exhaust pipe 12 or the like. Is easily released. Furthermore, the reducing agent addition valve cooling device 65 of the present embodiment reduces the pressure by blowing compressed air supplied from the air compressor 32 of the negative pressure generating device 30A through the compressed air supply pipe 53 for cooling to the radiation fins or the like. The agent addition valve 21 is forcibly cooled. By supplying a high-speed flow of compressed air accompanied by disturbance to the reducing agent addition valve cooling device 65 by the air compressor 23, the heat transfer coefficient in the cooling means can be greatly improved.

  Furthermore, the reducing agent supply pipe 22 in the present embodiment is connected to one end of a reducing agent discharge pipe 26 via a pressure regulator 61 instead of an orifice, and the other end of the reducing agent discharge pipe 26 is connected to the reducing agent tank 25. It is connected to the. Thereby, when the pressure of the urea water in the reducing agent supply pipe 22 reaches a predetermined value, a part of the urea water in the reducing agent supply pipe 22 is returned to the reducing agent tank 25, so that the reducing agent supply pipe The pressure of the urea water in 22 is maintained at a predetermined value, and the amount of urea water added to the exhaust pipe 12 is adjusted with high accuracy.

2. Exhaust Purification Device Control Method An example of a control flow of the exhaust purification device 10A performed by the control device 40A in the present embodiment will be described with reference to the flowcharts of FIGS. 4 to 5 and the configuration diagrams of FIGS. .

  First, when the internal combustion engine is started and the execution of this control flow is started, the compressed air supply three-way solenoid valve 51 is turned on in step S51 after START, and the air compressor 32 and the aspirator 31 are communicated with each other. Then, the driving of the air compressor 32 is started. Next, in step S53, the solenoid valve 33 is controlled to be turned on and opened, and then in step S54, the timer T is reset and the timer T starts counting.

  Next, after the reducing agent supply three-way solenoid valve 52 is turned on in step S55 to connect the reducing agent tank 25 and the reducing agent supply pump 23A, the reducing agent supply pump 23 is driven in step S56 to reduce the reducing agent tank 25. The filling of the urea water in the reducing agent supply path is started. As a result, the gas component in the reducing agent supply path is released to the reducing agent tank 25 via the aspirator 31 and the like by the positive pressure generated by the pumping of the urea water by the reducing agent supply pump 23A and the suction force generated by the aspirator 31. Start (state of FIG. 6). At this time, since the reducing agent purge compressed air supply pipe 54 and the reducing agent supply pump 23A are blocked by the reducing agent supply three-way solenoid valve 52, the compressed air supplied from the air compressor 32 is supplied only to the aspirator 31. Supplied.

  Next, in step S57, it is determined whether or not the value of the timer T is equal to or greater than a preset value T0. T0 is the time required for the gas component in the reducing agent supply path to be sufficiently released based on the discharge flow rate of the reducing agent supply pump 23A and the capacity of the reducing agent supply path, and is stored in the storage unit of the control device 40A. Pre-filled. If the value of timer T is less than T0, step S57 is repeated.

  When the value of the timer T is equal to or greater than T0, that is, when it is estimated that the gas component in the reducing agent supply path has been released, the process proceeds to step S58 where the driving of the air compressor 32 is stopped and the electromagnetic valve 33 is turned on. It is turned off and the reducing agent supply path and the aspirator 31 are shut off (state shown in FIG. 7). If suction from the reducing agent supply path is performed for a time longer than T0, the low-pressure urea water returns to the reducing agent tank 25 more than necessary via the aspirator 31, but the exhaust gas purification apparatus 10A is particularly suitable. There is no impact. However, when the pressure in the reducing agent supply path is maintained at a predetermined pressure, the driving energy of the reducing agent supply pump 23A increases.

Thereafter, urea water addition control is executed based on the NO _x concentration in the exhaust gas discharged from the internal combustion engine 11 in step S59. When the solenoid valve 33 is turned off and the aspirator 31 and the reducing agent supply path are shut off, the compressed air supply three-way solenoid valve 51 is turned off and the air compressor 32 and the aspirator 31 are shut off. It does not matter.

  In the present embodiment, while urea water addition control is executed during operation of the internal combustion engine 11, the temperature Ti of the reducing agent addition valve 21 is estimated in step S60, and the estimated temperature of the reducing agent addition valve 21 is determined in step S61. It is determined whether Ti is greater than or equal to a threshold value Ti0. The temperature of the reducing agent addition valve 21 can be estimated based on the exhaust temperature, the operating state of the internal combustion engine 11, or can be detected by a temperature sensor. The threshold value is a reference value for determining whether the reducing agent addition valve does not cause thermal damage.

  If the estimated temperature Ti of the reducing agent addition valve 21 is less than the threshold value Ti0, the process proceeds directly to step S64. On the other hand, if the estimated temperature Ti of the reducing agent addition valve 21 is greater than or equal to the threshold value Ti0, the three-way electromagnetic for supplying compressed air in step S62. The valve 51 is turned off, and the air compressor 32 and the reducing agent addition valve cooling device 65 are communicated. Then, the driving of the air compressor 32 is started in step S63, and the reducing agent addition valve 21 is cooled by supplying the compressed air to the reducing agent addition valve cooling device 65 (state of FIG. 8). Next, in step S64, it is determined whether or not the internal combustion engine 11 has stopped. Until the stop of the internal combustion engine 11 is detected in step S64, the steps S59 to S64 are repeated. However, steps S60 to S63 may be omitted.

  When the stop of the internal combustion engine 11 is detected in step S64, the compressed air supply three-way solenoid valve 51 is turned on in step S65, the air compressor 32 and the aspirator 31 are communicated, and in step S66, the air compressor 32 is turned on. Driving is started. Further, the reducing agent supply three-way solenoid valve 52 is turned off in step S67, the reducing agent purge compressed air supply pipe 54 and the reducing agent supply pump 23A are communicated, and in step S68, the solenoid valve 33 is turned on. The aspirator 31 and the reducing agent supply path communicate with each other.

  As a result, urea water remaining in the reducing agent supply path due to the positive pressure of the compressed air supplied into the reducing agent supply path via the reducing agent supply three-way solenoid valve 52 and the suction force generated by the aspirator 31. Is efficiently recovered in the reducing agent tank 25 (state shown in FIG. 9). Further, in the present embodiment, since it is not necessary to open the reducing agent addition valve 21 for introducing air into the reducing agent supply path, foreign substances such as unburned fuel and soot are reduced from the exhaust pipe 12. Intrusion into the agent supply path can be prevented.

  When recovery of urea water from the reducing agent supply path is completed, the temperature Ti of the reducing agent addition valve 21 is estimated in step S69, and it is determined whether or not the estimated temperature Ti of the reducing agent addition valve 21 is equal to or higher than a threshold value Ti0 in step S70. Is done. The temperature of the reducing agent addition valve 21 can be estimated based on the exhaust temperature or the like, or detected by a temperature sensor. The threshold value is a reference value for determining whether the reducing agent addition valve does not cause thermal damage.

  If the estimated temperature Ti of the reducing agent addition valve 21 is less than the threshold value Ti0, the process proceeds to step S72 as it is, and the air compressor 32 and other three-way valves are turned off to finish the control. On the other hand, when the estimated temperature Ti of the reducing agent addition valve 21 is equal to or higher than the threshold value Ti0, the compressed air supply three-way solenoid valve 51 is turned off in step S71, and the air compressor 32 and the reducing agent addition valve cooling device 65 are communicated. The Thus, the reducing agent addition valve 21 is cooled by supplying the compressed air to the reducing agent addition valve cooling device 65 (state of FIG. 10). This is particularly effective when the vehicle is stopped, where the heat dissipation effect due to the traveling wind cannot be expected. Then, after the reductant addition valve 21 is cooled for a predetermined time, the process proceeds to step S72, and the air compressor 32 and other three-way valves are turned off to end the control. However, steps S69 to S71 may be omitted.

10 · 10A: exhaust gas purification apparatus, 11: engine, 12: exhaust pipe, 13: exhaust gas temperature sensor, 14: SCR catalyst 15: ammonia slip catalyst 16: NO _X sensor, 20 · 20A: reducing agent addition device, 21: Reducing agent addition valve, 22: Reducing agent supply pipe, 23 / 23A: Reducing agent supply pump, 24: Reducing agent feeding pipe, 25: Reducing agent tank, 26: Reducing agent discharge pipe, 27: Orifice, 28: Reducing agent addition valve cooling device, 29: reducing agent pressure sensor, 30 / 30A: negative pressure generating device, 31: aspirator, 32: air compressor, 33: solenoid valve, 34: compressed air supply pipe, 35: gas suction pipe, 36: Gas release pipe, 37: Pressure adjusting valve, 40 / 40A: Control device, 51: Three-way solenoid valve for supplying compressed air, 52: Three-way solenoid valve for supplying reducing agent, 53: Compressed air supply pipe for cooling, 54: reduction Compressed compressed air supply pipe, 61: pressure regulator, 63: cooling water flow rate adjustment valve, 65: reducing agent addition valve cooling device, 71: driving fluid supply port, 73: driving fluid discharge port, 75: suction port, 77: Aperture part

Claims (4)

An exhaust emission control device that purifies exhaust gas from an internal combustion engine using an SCR catalyst and a reducing agent, the reducing agent tank for storing the reducing agent, and a reducing agent addition valve for adding the reducing agent upstream of the SCR catalyst; An exhaust gas purification apparatus comprising: a reducing agent supply pump for supplying the reducing agent from the reducing agent tank to the reducing agent addition valve via a reducing agent supply path;
E Bei negative pressure generating means for releasing the reducing agent supply path outside by sucking gas component of the reducing agent supply path,
The exhaust gas purification device according to claim 1, wherein the negative pressure generating means is an aspirator and is operated by compressed air supplied by an air compressor . The exhaust purification device according to claim 1, wherein the negative pressure generating means is connected to the reducing agent supply path via an electromagnetic valve. A reducing agent supply path between the reducing agent tank and the reducing agent supply pump includes a three-way solenoid valve, and is configured to be able to supply at least a part of the compressed air supplied by the air compressor to the reducing agent supply path. The exhaust emission control device according to claim 1 , wherein the exhaust purification device is provided. A reducing agent tank for storing the reducing agent, a reducing agent addition valve for adding the reducing agent to the upstream side of the SCR catalyst, and supplying the reducing agent from the reducing agent tank to the reducing agent addition valve via a reducing agent supply path In a control method of an exhaust gas purification device comprising a reducing agent supply pump for
At the start of the internal combustion engine, the reducing agent supply pump operates the negative pressure generating means while supplying the reducing agent to the reducing agent supply path, and sucks the gas component in the reducing agent supply path to thereby reduce the reducing agent. A control method for an exhaust gas purification apparatus, wherein the exhaust gas is discharged out of a supply path.

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