JP6172468B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine that purifies harmful substances in the exhaust gas with a liquid such as urea water added to an exhaust passage.

  Conventionally, a urea SCR system is known as one of exhaust gas purification apparatuses for internal combustion engines. In the urea SCR system, a catalyst (SCR catalyst, NOx selective reduction catalyst) that selectively reduces and purifies NOx in the exhaust is provided in the exhaust passage. An addition valve for adding urea water as a reducing agent in the exhaust gas is provided upstream of the catalyst. The catalyst converts urea water added from the addition valve into ammonia and stores it, and decomposes NOx in the exhaust gas into nitrogen and water with the stored ammonia, that is, reduces it.

  The urea water added to the exhaust has a property of freezing at -11 ° C. When the urea water freezes, the volume of the urea water increases, that is, the urea water expands. If the urea water remaining in the urea water supply system (addition valve, pump, piping, etc.) for supplying urea water to the exhaust passage expands due to freezing, the urea water supply system may be damaged by the expansion. Therefore, conventionally, after the internal combustion engine is stopped, the urea water remaining in the urea water supply system is sucked back into the urea water tank by driving the pump in a reverse rotation (see, for example, Patent Document 1). .

  In Patent Document 1, a branch pipe is provided in the vicinity of the urea water addition valve, an intake valve (check valve) is provided in the branch pipe, and when the urea water is sucked back into the urea water tank, the addition valve is not provided. It is disclosed that air is introduced into a pipe from the intake valve after the valve is closed. According to this, the urea water can be sucked back while preventing the foreign matter from being sucked into the addition valve from the exhaust passage.

JP 2008-101564 A

  However, in the method of Patent Document 1, there is a possibility that foreign matter may be mixed into the addition valve from the branch pipe and the intake valve, and there is a problem that the function of the addition valve is deteriorated when foreign matter is mixed into the addition valve. Further, if a liquid such as urea water remains in the pump and expands, the pump components (such as a sensor in the pump) may be damaged. Therefore, it is necessary to suppress the liquid from remaining in the pump.

  The present invention has been made in view of the above problems, and when sucking back the liquid into the tank, it is possible to prevent foreign matter from being mixed into the addition valve, and the liquid remaining in the pump can be efficiently put into the tank. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine that can be sucked back.

In order to solve the above problems, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a tank in which a liquid for purifying harmful substances in the exhaust gas of the internal combustion engine is stored,
An addition valve for adding the liquid to the exhaust passage of the internal combustion engine;
A pipe forming a flow path for the liquid between the tank and the addition valve;
When the liquid is added to the exhaust passage by the addition valve connected to the pipe, the liquid is sucked up from the tank, and the liquid is sucked back into the tank after the internal combustion engine is stopped. A pump,
Introducing means for introducing air into the pipe when the liquid is sucked back into the tank by connecting to any part of the pipe from the pump to the addition valve;
A flow path closing means for closing the flow path of the pipe communicating with the addition valve from the connecting portion which is a part of the pipe to which the introducing means is connected, when sucking the liquid back into the tank;
Equipped with a,
The introduction means and the flow path closing means are:
Provided in the connection part, opens a flow path of a tank side pipe that is the pipe on the tank side from the connection part and a flow path of an addition valve side pipe that is the pipe on the addition valve side from the connection part. A first flow path state that closes the flow path of the introduction means, a flow path of the tank side pipe and a flow path of the introduction means are opened, and the flow path of the addition valve side pipe is closed A switching valve for switching between the flow path states;
Switching control means for setting the switching valve in the first flow path state when adding the liquid to the exhaust passage and for setting the switching valve in the second flow path state when sucking the liquid back into the tank. And
The switching control means switches the switching valve to the second flow path state after starting to suck back the liquid into the tank .

  According to the present invention, when sucking back the liquid, air is introduced into the pipe from the part (connecting portion) of the pipe to which the introducing means is connected, so that the liquid is sucked back into the tank effectively. Can do. At the time of this sucking back, the flow path of the pipe that communicates from the connecting portion to the addition valve is closed, so that foreign matter can be prevented from being mixed from the introduction means or the pump side to the addition valve side. Moreover, the liquid remaining on the pump side can be sucked back efficiently by closing the flow path of the pipe leading to the addition valve.

It is a block diagram of an exhaust gas purification system. It is sectional drawing which showed the whole structure of the addition valve. It is the A section enlarged view of FIG. It is the B section enlarged view of FIG. It is a flowchart of the suck back process of 1st Embodiment. It is a 1st example of the flowchart of a three-way valve switching process. It is a 2nd example of the flowchart of a three-way valve switching process. It is a flowchart of the suck back process of 2nd Embodiment. It is a flowchart of the suck back process of 3rd Embodiment. It is a block diagram of the exhaust gas purification system which concerns on a modification.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an exhaust purification system 1 mounted on a vehicle. The exhaust purification system 1 corresponds to the “exhaust purification device for an internal combustion engine” of the present invention, and is a urea SCR system that purifies NOx in exhaust discharged from a diesel engine 2 (hereinafter simply referred to as an engine) as an internal combustion engine. Has been built. In the exhaust purification system 1, an exhaust passage 3 is connected to the engine 2, and exhaust from the engine 2 is exhausted outside the vehicle through the exhaust passage 3.

The exhaust passage 3 is provided with an SCR catalyst 4 (NOx selective reduction catalyst) that selectively reduces NOx in the exhaust. The SCR catalyst 4 converts urea water (reducing agent) added from an addition valve 5 described later into ammonia (NH 3) by hydrolysis and stores the ammonia. Then, the SCR catalyst 4 decomposes (purifies) NOx into water or nitrogen by causing the stored ammonia (NH3) and NOx in the exhaust to react, for example, by the following formula 1, formula 2, and formula 3.
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 3H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)

  The SCR catalyst 4 cannot store ammonia inexhaustably, and the maximum amount of ammonia that can be stored in the SCR catalyst 4 varies depending on the temperature of the SCR catalyst 4 (catalyst temperature). For example, when the catalyst temperature rapidly decreases, a phenomenon called ammonia slip in which ammonia is released from the SCR catalyst 4 occurs. Therefore, an oxidation catalyst (not shown) for purifying ammonia released from the SCR catalyst 4 by ammonia slip may be provided downstream of the SCR catalyst 4 in the exhaust passage 3. The oxidation catalyst has an oxidation function and decomposes ammonia into water and nitrogen.

  The exhaust purification system 1 is provided with a urea water supply system that supplies urea water upstream of the SCR catalyst 4 in the exhaust passage 3 in order to supply urea water to the SCR catalyst 4. Specifically, an addition valve 5 (injector) for adding (supplying) urea water to the exhaust passage 3 is provided upstream of the SCR catalyst 4 in the exhaust passage 3. The addition valve 5 has the same structure as a fuel injection valve that injects fuel into the cylinder of the engine 2. 2 and 3 are structural views of the addition valve 5. Specifically, FIG. 2 is a cross-sectional view showing the entire configuration of the addition valve 5, and FIG. 3 is a part A of FIG. It is an enlarged view.

  The details of the structure of the addition valve 5 will be described with reference to FIGS. 2 and 3. The addition valve 5 is an electromagnetic on-off valve provided with a drive part 51 and a valve body part 52. The drive unit 51 includes an electromagnetic solenoid 53 and is energized by an energization signal input from the terminal 54. The main part of the valve body 52 is a needle 56 housed in the casing 55 and a nozzle body 57 that is assembled to the casing 55 and holds the tip of the needle 56 slidably. A coil spring 58 for urging the needle 56 in the valve closing direction.

  In the needle 56 and the nozzle body 57, urea water passages 59 and 60 (see FIG. 3) for allowing the urea water taken from the urea water suction port 63 to flow are provided. A plurality of urea water circulation holes 61 are formed on the side surface near the tip of the needle 56. The urea water passages 59 and 60 are communicated with each other through the urea water circulation hole 61. After passing through the urea water passage 59, the urea water proceeds from the urea water circulation hole 61 to the urea water passage 60. Further, a tip jet outlet 62 (see FIG. 3) is formed at the tip of the nozzle body 57.

  When the electromagnetic solenoid 53 is energized to the energization signal from the DCU 19 (see FIG. 1), the addition valve 5 moves the needle 56 in the valve opening direction along with the energization. It is opened and urea water is added (injected).

  Returning to the description of FIG. 1, urea water is sequentially supplied from the urea water tank 6 to the addition valve 5. The urea water tank 6 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration is stored therein. The upper part 602 in the urea water tank 6 is a space that is not filled with urea water. The space portion 602 is separated from the outside by a wall surface 601 (corresponding to a “partition wall” of the present invention) of the urea water tank 6.

  Between the urea water tank 6 and the addition valve 5, for example, a rubber pipe 8 that forms a flow path of urea water is provided. One end 83 of the pipe 8 is connected to the urea water inlet 63 (see FIG. 2) of the addition valve 5, and the other end 84 is connected to the pump 7. The pump 7 includes a main body 71 and a suction port 72 for sucking urea water into the main body 71. In the present embodiment, the main body 71 is arranged at a position adjacent to the urea water tank 6 outside the urea water tank 6. The suction port 72 is disposed in the urea water tank 6 so as to be immersed in the urea water.

  The pump 7 (main body 71) is an in-line electric pump (for example, a three-phase AC motor) that is rotationally driven by a drive signal from the DCU 19, and can rotate in either the forward or reverse direction. When the pump 7 is rotationally driven in the forward rotation direction (hereinafter referred to as forward rotation driving), the urea water is pumped up from the urea water tank 6, and the urea water passes through the main body 71 and is added through the pipe 8. Discharge (pressure feeding) to the valve 5 side. On the contrary, when the pump 7 is rotationally driven in the reverse rotation direction (hereinafter referred to as reverse rotation driving), the urea water filled in the urea water supply system (pipe 8, pump 7, etc.) is sucked back into the urea water tank 6. Be able to. In FIG. 1, the main body 71 is provided outside the urea water tank 6, but may be provided in a state immersed in the urea water in the urea water tank 6.

  The main body 71 includes a motor (stator, rotor, etc.) constituting an electric pump, a drive circuit for driving the motor, an impeller fitted to the rotation shaft of the motor, and a sensor (main body for driving the pump 7). 71, a sensor for detecting the pressure of the urea water in 71, a sensor for detecting the temperature of the urea water, and the like.

  A branch pipe 10 branched from the pipe 8 is connected to the middle of the pipe 8. The branch pipe 10 is provided in the vicinity of the urea water tank 6 and the pump 7. Specifically, one end 11 of the branch pipe 10 is connected to a portion of the pipe 8 from the pump 7 to the addition valve 5 that is closer to the pump 7 than the addition valve 5. More specifically, the end 11 of the branch pipe 10 is connected to a portion of the pipe 8 that is located immediately above the pump 7. Further, a through hole is formed in the upper wall surface 601 of the urea water tank 6, and the other end 12 of the branch pipe 10 is connected to the wall surface 601 so as to fit the through hole. That is, the end portion 12 of the branch pipe 10 is connected to the space portion 602 in the urea water tank 6.

  In addition, a check valve 13 having a structure that allows the flow of fluid in one direction and prohibits the flow of fluid in the opposite direction (back flow) is disposed in the flow path of the branch pipe 10. . The arrangement direction of the check valve 13 is an arrangement direction that allows fluid to flow from the end portion 12 toward the end portion 11 and prohibits fluid from flowing from the end portion 11 toward the end portion 12. Yes. The check valve 13 is composed of a mechanical check valve that opens and closes by a balance between the biasing force of the built-in spring and the urea water pressure. When the pump 7 is driven in reverse, the check valve 13 is opened by the negative pressure in the pipe 8.

  Further, a three-way valve 9 is provided at a connection portion that is a part of the pipe 8 to which the branch pipe 10 is connected. Here, FIG. 4 is an enlarged view of a portion B in FIG. As shown in FIG. 4, the three-way valve 9 has an opening / closing part 91 connected to a branch pipe 10 and a branch point 100 (connection part) of the pipe 8. The opening / closing part 91 is switched to either the position C or the position D shown in FIG. 4 with the branch point 100 as a base point, whereby the flow path of the branch pipe 10 is opened / closed. Specifically, when the opening / closing part 91 is at the position C, the flow path of the branch pipe 10 is closed, the flow path of the pipe 81 (addition valve side pipe) on the addition valve 5 side from the connection part, and the connection part The pipe 82 (tank side pipe) on the urea water tank 6 side (pump 7 side) opens. On the other hand, when the opening / closing part 91 is at the position D, the flow path of the branch pipe 10 and the flow path of the tank side pipe 82 are opened, and the flow path of the addition valve side pipe 81 is viewed from the tank side pipe 82. It closes (the flow path of the tank side pipe 82 and the flow path of the addition valve side pipe 81 are blocked). Hereinafter, the state where the opening / closing part 91 is at the position C is referred to as a first flow path state, and the state where the opening / closing part 91 is at the position D is referred to as a second flow path state.

  The addition valve side pipe 81 is provided with a pressure sensor 14 that detects the pressure in the addition valve side pipe 81. Further, a porous urea water filter (not shown) for filtering urea water is provided in the middle of the pipe 8.

  Further, upstream of the addition valve 5 in the exhaust passage 3, a NOx sensor 15 for detecting the NOx concentration in the exhaust (NOx concentration before passing through the SCR catalyst 4) and an exhaust temperature sensor 16 for detecting the exhaust temperature are provided. ing. An exhaust temperature sensor 17 for detecting the exhaust temperature is provided between the addition valve 5 in the exhaust passage 3 and the SCR catalyst 4. Further, a NOx sensor 18 for detecting the NOx concentration in the exhaust gas (NOx concentration after passing through the SCR catalyst 4) is provided downstream of the SCR catalyst 4 in the exhaust passage 3. These sensors 15 to 18 are used, for example, to control the amount of urea water added by the addition valve 5 and the addition timing.

  The exhaust purification system 1 includes a DCU (Dosing Control Unit) 19. The DCU 19 includes a known microcomputer. While the engine 2 is operating (ON), urea water is added to the exhaust passage 3 by the addition valve 5 based on the detection values of various sensors (ureation time of urea water). , The amount added). The DCU 19 controls the driving of the three-way valve 9 and the pump 7. Specifically, when the urea water is added by the addition valve 5, the DCU 19 sets the three-way valve 9 in the first flow path state (position C in FIG. 4). The pump 7 is driven to rotate forward. As a result, the branch pipe 10 is closed, so that urea water flowing in the pipe 8 can be prevented from flowing into the branch pipe 10, and air and foreign matter are introduced from the branch pipe 10 into the pipe 8. Can be suppressed. Therefore, urea water can be efficiently sent to the addition valve 5 and foreign matter can be prevented from entering the addition valve 5.

  Here, the urea water freezes at -11 ° C., and the volume increases by about 7% when frozen. Therefore, when urea water is filled in the urea water supply system (the addition valve 5, the pipe 8, the pump 7, etc.) when the engine 2 is stopped, the urea water supply system is expanded due to volume expansion due to freezing of the urea water. May be damaged. On the other hand, the present inventor considers that the urea water remains in the pump 7 is more problematic than the urea water remains in the addition valve 5. The main body 71 of the pump 7 is provided with a motor, a sensor necessary for driving the pump 7 (motor), etc. When the urea water freezes and expands, they are damaged and the function of the pump 7 is lowered. Because it will do.

  In addition, it is necessary to avoid contamination of the addition valve 5 when the urea water remaining in the urea water supply system is sucked back into the urea water tank 6. If foreign matter is mixed into the addition valve 5, as shown in FIG. 3, the tip jet outlet 62 is clogged with foreign matter, the foreign matter is caught by the needle 56, and the function of the addition valve 5 is degraded. It is.

  Based on the above problems, the DCU 19 performs a suck-back process for sucking (recovering) the urea water remaining in the urea water supply system after the engine 2 is stopped into the urea water tank 6. Hereinafter, details of this suck back processing will be described. FIG. 5 is a flowchart of the suck back process. The process of FIG. 5 is repeatedly executed at predetermined time intervals while the DCU 19 is operating.

  When the processing of FIG. 5 is started, the DCU 19 first determines whether both the stop of the engine 2 and the stop of the pump 7 are satisfied as a determination as to whether or not the execution condition of the urea water suction back control is satisfied. Is determined (S11). The stop of the engine 2 may be determined based on, for example, whether or not an ignition switch (not shown) for turning on and off the engine 2 is turned off. If neither the stop of the engine 2 nor the stop of the pump 7 is established, that is, if at least one of the engine 2 and the pump 7 is operating (S11: No), the processing of FIG. In this case, urea water suck-back control is not executed.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S11: Yes), the process proceeds to S12, and the three-way valve 9 is in the second flow path state (the state of the position D in FIG. 4). Switch to. Thereafter, the pump 7 is driven in reverse, and the urea water remaining in the urea water supply system is sucked back into the urea water tank 6 (S13). As a result, the air in the space 602 is introduced into the pipe 8 through the branch pipe 10 and the check valve 13. And the air introduced in the piping 8 distribute | circulates the tank side piping 82 and the inside of the pump 7 (main-body part 71). Therefore, the urea water remaining in the tank side pipe 82 and the pump 7 can be sucked back into the urea water tank 6 through the suction port 72 (in this case, functioning as a discharge port).

  In addition, it is preferable to keep the addition valve 5 closed when sucking back urea water. As a result, it is possible to prevent foreign matter from entering the addition valve 5 from the exhaust passage 3.

  The suck back control is executed for a predetermined time. This predetermined time is added so that urea water does not remain in the urea water supply system after execution of the suck back control, or even if it remains, a space that can absorb the expansion volume when urea water expands due to freezing is added. It is set to exist in the valve 5. After executing the suck back control, the process of the flowchart of FIG. 5 is terminated. The DCU 19 turns on an end flag indicating that the suck-back process in FIG. 5 has ended.

  The suck-back process in FIG. 5 is a process up to the end of the urea water suck-back, but it is necessary to return the three-way valve 9 switched to the second flow path state to the original first flow path state at the time of suck-back. is there. Therefore, the DCU 19 executes, for example, a three-way valve switching process shown in FIG. 6 or FIG. The three-way valve switching process of FIGS. 6 and 7 is executed in parallel with the suck back process of FIG. 5 and is repeatedly executed at predetermined intervals while the DCU 19 is operating.

  First, the processing of FIG. 6 will be described. When the processing of FIG. 6 is started, the DCU 19 determines whether or not the end flag is turned on, that is, whether or not the urea water suction is completed (S31). If the end flag is off (S31: No), the process of FIG. On the other hand, when the end flag is turned on (S31: Yes), it is determined that the urea water sucking back has ended, and the three-way valve 9 is moved from the second flow path state (the state at the position D in FIG. 4) to the first. Switching to the flow path state (the state at position C in FIG. 4) (S32). Then, the process of FIG. 6 is complete | finished.

  According to the processing of FIG. 6, since the three-way valve 9 is switched to the original position based on the end of the urea water sucking back, the engine 2 is started after that and the urea water is supplied by the addition valve 5. At the time of addition, urea water can be supplied from the urea water tank 6 to the addition valve 5.

  Next, the process of FIG. 7 will be described. When the processing of FIG. 7 is started, the DCU 19 determines whether or not the engine 2 has been started based on whether or not the ignition switch is turned on (S41). When the engine 2 is stopped (S41: No), the process of FIG. 7 is terminated. When the engine 2 is started (S41: Yes), the three-way valve 9 is switched from the second flow path state (the position D in FIG. 4) to the first flow path state (the position C in FIG. 4) ( S42). Thereafter, the process of FIG.

  According to the processing of FIG. 7, since the three-way valve 9 is switched to the original position based on the start of the engine 2, the urea water is added when the urea water is added by the addition valve 5 after the engine 2 is started. Water can be supplied from the urea water tank 6 to the addition valve 5.

  As described above, according to the present embodiment, since the three-way valve 9 is switched to the second flow path state in advance and the addition valve side pipe 81 is closed before the urea water is sucked back, the addition valve side It can suppress that a foreign material mixes into the pump 7 side from the piping 81 and the addition valve 5 side. On the contrary, it can suppress that a foreign material mixes into the addition valve side piping 81 and the addition valve 5 side from the pump 7 and the branch pipe 10 side. In addition, by closing the addition valve side pipe 81, air can be efficiently circulated through the tank side pipe 82 and the pump 7. As a result, the urea water remaining in the tank side pipe 82 and the pump 7 is removed. Can be sucked back efficiently. Therefore, damage to the pump 7 can be effectively suppressed.

  In addition, since one end 11 of the branch pipe 10 is disposed immediately above the pump 7 and the other end 12 is connected to the urea water tank 6, it is possible to prevent the branch pipe 10 from becoming long. That is, it is possible to simplify the configuration related to urea water sucking back. In addition, since the upstream side of the check valve 13 (the end portion 12 of the branch pipe 10) is connected to the space portion 602 separated from the outside, foreign matter such as water is introduced into the pipe 8 from the check valve 13. It can suppress mixing. Therefore, it is possible to suppress a decrease in the function of the urea water supply system. By using the space part 602 of the urea water tank 6, it is not necessary to prepare a separate space part, so that the configuration can be simplified.

  Furthermore, since the air introduction means (three-way valve 9, branch pipe 10, check valve 13) to the pipe 8 is disposed closer to the pump 7 than the addition valve 5, there is a foreign matter in the pipe 8 from the air introduction means. Can be prevented from entering the addition valve 5, and air can be efficiently circulated through the tank side pipe 82 and the pump 7.

  In this embodiment, since the mechanical check valve 13 (check valve) is used, air can be introduced from the check valve 13 to the pipe 8 without controlling the operation of the check valve 13. The backflow of air can be prevented from the pipe 8 to the check valve 13 side.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on the differences from the above embodiment. The configuration of the exhaust purification system of this embodiment is the configuration of FIG. The suck back process executed by the DCU 19 is different from that of the first embodiment, and other than that is the same as that of the first embodiment. The DCU 19 executes the suck back process shown in FIG. Hereinafter, details of the suck-back process in FIG. 8 will be described. The process of FIG. 8 is repeatedly executed at predetermined intervals while the DCU 19 is operating.

  When the processing of FIG. 8 is started, the DCU 19 first determines whether both the stop of the engine 2 and the stop of the pump 7 are satisfied as a determination as to whether or not the execution condition of the urea water suction back control is satisfied. Is determined (S21). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S21: No), the process of FIG. 8 is terminated.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S21: Yes), the pump 7 is driven in reverse to start sucking back urea water (S22). The measurement of elapsed time is started (S23). For example, a timer (not shown) provided in the DCU 19 may be used for the time measurement. At the start of sucking back, the three-way valve 9 remains in the first flow path state (the state at the position C in FIG. 4). Therefore, urea water is sucked back into the entire urea water supply system for a while from the start, and the pressure in the addition valve side pipe 81 and the addition valve 5 decreases with the progress of the sucking back. . The addition valve 5 may be opened or closed while the urea water supply system is sucking back the entire urea water supply system. By making the addition valve 5 open, the pressure in the addition valve 5 can be efficiently reduced. Moreover, it can suppress that the foreign material from the exhaust passage 3 mixes in the addition valve 5 by making the addition valve 5 into a valve closing state.

  Next, it is determined whether or not the elapsed time from the start of sucking has reached a predetermined time (S24). This predetermined time is a time set by experiment or calculation so that the pressure in the addition valve side pipe 81 and the addition valve 5 is less than the predetermined pressure. If the elapsed time has not yet reached the predetermined time (S24: No), the process waits until the predetermined time is reached. When the elapsed time reaches the predetermined time (S24: Yes), the three-way valve 9 is switched to the second flow path state (the state at the position D in FIG. 4) (S25). As a result, the suction back on the addition valve 5 side stops and the suction back on the pump 7 side continues. Thereafter, after performing the suck back control for a predetermined time, the pump 7 is stopped and the suck back control is terminated (S26). Then, the process of the flowchart of FIG. 8 is complete | finished. Similarly to the first embodiment, the DCU 19 executes the processing of FIG. 6 or FIG. 7 and moves the three-way valve 9 from the second flow path state to the first flow based on the end of the suck back and the start of the engine 2. Return to the road condition.

  As described above, according to this embodiment, the same effect as that of the above embodiment can be obtained. In addition, in the present embodiment, since the three-way valve 9 is switched after a predetermined time has elapsed from the start of the urea water suction back, the pressure in the addition valve side pipe 81 and the addition valve 5 can be lowered. Thereby, even if the urea water remaining in the addition valve side pipe 81 and the addition valve 5 expands due to freezing, an increase in volume at the time of expansion can be suppressed, and the addition valve side pipe 81 and the addition valve 5 Damage can be suppressed.

(Third embodiment)
Next, a third embodiment of the present invention will be described focusing on the differences from the above embodiment. The configuration of the exhaust purification system of this embodiment is the configuration of FIG. The suck-back process executed by the DCU 19 is different from the first and second embodiments, and the rest is the same as the first and second embodiments. The DCU 19 executes the suck back process shown in FIG. Hereinafter, details of the suck-back process in FIG. 9 will be described. The processing in FIG. 9 is repeatedly executed at predetermined intervals while the DCU 19 is operating.

  When the processing of FIG. 9 is started, the DCU 19 first determines whether both the stop of the engine 2 and the stop of the pump 7 are satisfied as a determination as to whether or not the execution condition of the urea water suction back control is satisfied. Is determined (S51). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S51: No), the process of FIG. 9 is terminated.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S51: Yes), the pump 7 is driven in reverse to start sucking back urea water (S52). As in the second embodiment, first, urea water is sucked back into the entire urea water supply system including the addition valve side pipe 81 and the addition valve 5. Further, the addition valve 5 may be opened or closed.

  Next, the urea water pressure P (pressure in the addition valve side pipe 81) detected by the pressure sensor 14 (see FIG. 1) is read (S53). Next, it is determined whether the urea water pressure P is higher than a predetermined pressure (S54). When the urea water pressure P is lower than the predetermined pressure (S54: No), the three-way valve 9 is switched to the second flow path state (position D in FIG. 4) (S58). As a result, the suction back on the addition valve 5 side stops and the suction back on the pump 7 side continues. Thereafter, after performing the suck back control for a predetermined time, the pump 7 is stopped, the suck back control is ended (S59), and the processing of the flowchart of FIG. 9 is ended.

  On the other hand, if the urea water pressure P is higher than the predetermined pressure in S54 (S54: Yes), an interval (standby time) is provided until the urea water pressure P is read next (S55). The length of this interval is changed according to the value of the urea water pressure P read last time. Specifically, the higher the urea water pressure P, the longer the interval. For example, the relationship (map) between the urea water pressure P and the length of the interval is stored in advance in a memory in the DCU 19, and the length of the interval corresponding to the current urea water pressure P is determined based on this relationship. It ’s fine.

  After the interval set in S55 has elapsed, the urea water pressure P is read again from the pressure sensor 14 (S56), and it is determined whether or not the urea water pressure P has become lower than a predetermined pressure (S57). If it is not yet lowered (S57: No), the process returns to S55, and an interval is provided again based on the urea water pressure P read immediately before (S55), and the urea water pressure P is read again after the interval has passed (S55). S56).

  When the urea water pressure P becomes lower than the predetermined pressure in S57 (S57: Yes), the three-way valve 9 is switched to the second flow path state (S58), and the suck back control is ended (S59). Similarly to the first and second embodiments, the DCU 19 executes the process of FIG. 6 or FIG. 7 to move the three-way valve 9 from the second flow path state based on the end of the suck back or the start of the engine 2. Return to the first flow path state.

  As described above, according to this embodiment, the same effect as that of the above embodiment can be obtained. In addition, in this embodiment, since the three-way valve 9 is switched after the urea water pressure P becomes lower than the predetermined pressure after the start of the urea water sucking back, the pressure in the addition valve side pipe 81 and the addition valve 5 is changed. Can be reliably lowered. Thereby, even if the urea water remaining in the addition valve side pipe 81 and the addition valve 5 expands due to freezing, an increase in volume at the time of expansion can be suppressed, and the addition valve side pipe 81 and the addition valve 5 Damage can be suppressed.

  In addition, this invention is not limited to the said embodiment, A various change is possible to the limit which does not deviate from description of a claim. For example, in the above embodiment, the upstream side of the check valve (branch pipe) is connected to the urea water tank (space), but as shown in FIG. 10, the upstream side of the check valve 13 is opened (no connection). (It may be connected to a space having no partition wall). The exhaust purification system 1a of FIG. 10 is the same as the configuration of FIG. 1 except that the upstream side of the check valve 13 (branch pipe 10a) is opened. As a result, the branch pipe 10a can be shortened, and the configuration can be simplified. Further, the upstream side of the check valve may be connected to a space having a partition wall other than the urea water tank.

  Moreover, in the said embodiment, although the three-way valve was arrange | positioned in the connection part of a branch pipe and piping, you may abbreviate | omit this three-way valve. This also makes it possible to suck back urea water. Even if the three-way valve is omitted, air introduction means (branch pipe, check valve) are arranged on the pump side, so that air, foreign matter, etc. introduced into the pipe from the air introduction means are less likely to enter the addition valve. In addition, air can be efficiently circulated to the pump side, and the urea water remaining on the pump side can be sucked back efficiently.

  In the above embodiment, an example in which a check valve is arranged in the branch pipe has been described. However, when a configuration in which a three-way valve is arranged in the connection portion is adopted, the check valve may be omitted. This also prevents the urea water from flowing back through the branch pipe because the branch pipe is closed by the three-way valve when the urea water is added by the addition valve.

  Further, instead of the three-way valve and the mechanical check valve, an intake valve (for example, a shutter valve) that electrically opens and closes the flow path of the branch pipe may be employed. In this case, when adding urea water with the addition valve, the intake valve is closed and the flow path of the branch pipe is closed. As a result, the urea water can be prevented from flowing back through the branch pipe. Further, when sucking back urea water, the intake valve is opened and the branch pipe is opened. As a result, air can be introduced into the pipe from the intake valve, and urea water can be sucked back.

  Moreover, in the said embodiment, although the three-way valve is arrange | positioned in the connection part of a branch pipe and piping, this three-way valve is abbreviate | omitted and any of the piping (addition valve side piping) of the addition valve side rather than a connection part. An open / close valve (such as a shutter valve) for opening and closing the flow path may be provided at such a position. In this case, when adding urea water with the addition valve, the on-off valve is opened and the addition valve side pipe is opened. In contrast, when the urea water is sucked back, the on-off valve is closed and the addition valve side pipe is closed. Also by this, it is possible to avoid the air and foreign matter introduced into the pipe from the connecting portion from flowing into the addition valve, and to efficiently suck back the urea water on the pump side.

  Moreover, although the said embodiment demonstrated the example which has arrange | positioned the air introduction means (a branch pipe, a check valve, a three-way valve) on the pump side, the air introduction means is located on the addition valve side (position closer to the addition valve than the pump). ). Also by this, the presence of the three-way valve can prevent the air or foreign matter introduced into the pipe from the air introduction means from entering the addition valve, and can efficiently suck back the urea water on the pump side. .

  Further, before starting the sucking back of the urea water, the urea water pressure P is read from the pressure sensor 14 (see FIG. 1), and when the urea water pressure P is lower than the predetermined pressure, the three directions before the sucking back is started. When the valve 9 is switched to the second flow path state and the urea water pressure P is higher than the predetermined pressure, the processing after S22 in FIG. 8 or the processing after S52 in FIG. 9 may be executed.

  Moreover, in the said embodiment, although the pump which can be rotated to any direction forward / reverse was employ | adopted, the flow path connected to the pump which can be rotated only in the forward direction, and the inlet and outlet of the pump Alternatively, a flow path switching valve that switches between a flow path on the addition valve side and a flow path on the urea water tank side from the pump may be employed. In this case, when adding urea water with the addition valve, the flow path on the urea water tank side is connected to the suction port of the pump, and the flow path on the addition valve side is connected to the discharge port of the pump. Control the path switching valve. On the other hand, when sucking back urea water, the flow path on the addition valve side is connected to the suction port of the pump, and the flow path on the urea water tank side is connected to the discharge port of the pump. Controls the switching valve.

  For example, the present invention may be applied to a urea SCR system for a gasoline engine, particularly a lean burn engine. Further, the present invention may be applied to an exhaust purification system that uses a reducing agent other than urea water (for example, an aqueous solution containing ammonia).

  In the above embodiment, the DCU 19 that controls the three-way valve 9, the branch pipe 10, the check valve 13, and the three-way valve 9 corresponds to the “introducing means” in the present invention. The three-way valve 9 and the DCU 19 that controls the three-way valve 9 correspond to the “flow path closing means” in the present invention. The DCU 19 corresponds to “addition valve control means” in the present invention. The three-way valve 9 corresponds to a “switching valve” in the present invention. The SCU in FIG. 5, S25 in FIG. 8, S53 to S58 in FIG. 9, and the DCU 19 that executes the processes in FIGS. 6 and 7 correspond to the “switching control means” in the present invention. The pressure sensor 14 corresponds to the “pressure detection means” in the present invention.

1, 1a Exhaust gas purification system (exhaust gas purification device for internal combustion engine)
2 Diesel engine (internal combustion engine)
3 Exhaust passage 5 Addition valve 6 Urea water tank (tank)
7 Pump 8 Piping 9 Three-way valve 10 Branch pipe 13 Check valve 19 DCU

Claims (11)

A tank (6) in which a liquid for purifying harmful substances in the exhaust gas of the internal combustion engine (2) is stored;
An addition valve (5) for adding the liquid to the exhaust passage (3) of the internal combustion engine;
A pipe (8) that forms a flow path for the liquid between the tank and the addition valve;
When the liquid is added to the exhaust passage by the addition valve connected to the pipe, the liquid is sucked up from the tank, and the liquid is sucked back into the tank after the internal combustion engine is stopped. A pump (7);
Introducing means (9, 10, 13, 19) connected to any part of the piping from the pump to the addition valve to introduce air into the piping when the liquid is sucked back into the tank ,
Flow path closing means (9, 19) for closing the flow path of the pipe leading to the addition valve from the connecting portion which is a part of the pipe to which the introduction means is connected when sucking the liquid back into the tank When,
Equipped with a,
The introduction means and the flow path closing means are:
A flow path of a tank side pipe (82) which is the pipe on the tank side from the connection part and an addition valve side pipe (81) which is the pipe on the addition valve side from the connection part. A first flow path state in which the flow path of the introduction means is closed, a flow path of the tank-side piping and a flow path of the introduction means are opened, and the addition valve side is opened. A switching valve (9) that switches between a second flow path state that closes the flow path of the piping;
Switching control means for setting the switching valve in the first flow path state when adding the liquid to the exhaust passage and for setting the switching valve in the second flow path state when sucking the liquid back into the tank. (19)
The switching control means (S25, S53 to S58) switches the switching valve to the second flow path state after starting to suck back the liquid into the tank . 1a).   The exhaust emission control device for an internal combustion engine according to claim 1, further comprising addition valve control means (19) for closing the addition valve when sucking the liquid back into the tank.   The exhaust purification of an internal combustion engine according to claim 1 or 2, wherein the introduction means prohibits introduction of air into the pipe when the liquid is added to the exhaust passage by the addition valve. apparatus.   The introduction means is located in the space portion (602) having the downstream side (11) connected to the connection portion and the upstream side (12) having air, and fluid is transferred from the space portion to the connection portion. The internal combustion engine according to any one of claims 1 to 3, further comprising a check valve (13) that allows flow and prohibits fluid from flowing from the connection portion toward the space portion. Engine exhaust purification system. Pressure detecting means (14) for detecting the pressure in the pipe,
The switching control means (S53 to S58) sets the switching valve to the first flow path state until the pressure detected by the pressure detecting means becomes less than a predetermined value, and after the pressure becomes less than the predetermined value. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the switching valve is switched to the second flow path state. The switching control means (S31, S32) switches the switching valve from the second flow path state to the first flow path state based on completion of sucking back the liquid into the tank. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4 . It said switch control means (S41, S42) is any one of the preceding claims, characterized in that switching from said second flow path state based on the internal combustion engine is started in the first channel state The exhaust gas purification apparatus for an internal combustion engine according to the item .   The exhaust purification device of an internal combustion engine according to claim 4, wherein the space portion includes a partition wall (601) that separates the outside and the inside of the space portion. The exhaust purification device of an internal combustion engine according to claim 8 , wherein the space portion is a space portion in the tank. The internal combustion engine according to claim 9 , wherein the downstream side of the check valve is connected to a portion of the piping from the pump to the addition valve that is closer to the pump than the addition valve. Exhaust purification device. The internal combustion engine according to any one of claims 1 to 10, wherein the liquid is urea water for reducing NOx in exhaust gas in a NOx selective reduction catalyst provided in the exhaust passage. Exhaust purification device.

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