JP6016127B2 - 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 components in the exhaust gas with a catalyst provided in an exhaust passage and a reducing agent supplied to the catalyst.

  Conventionally, a urea SCR system is known as one of exhaust gas purification systems 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 supply means (addition valve, pump, pipe, etc.) for supplying urea water to the exhaust passage expands due to freezing, the supply means may be damaged due to the expansion. Thus, conventionally, after the internal combustion engine is stopped, the urea water remaining in the supply means is recovered in a urea water tank as a storage unit by rotating the pump of the supply means in reverse (for example, a patent) Reference 1).

Japanese Patent No. 4730278

  However, since it is physically impossible to completely eliminate the reducing agent from the supply unit, water drops of the reducing agent remain in the supply unit even if the recovery of the reducing agent to the storage unit is executed. The remaining reducing agent dries over time (water evaporates), and the reducing agent solidifies (precipitates) by this drying. Then, the solidified reducing agent causes a problem that the piping is clogged or the sliding portion of the addition valve is fixed.

  Further, when the reducing agent in the supply unit is collected in the storage unit, it becomes necessary to refill the supply unit with the reducing agent again at the next operation of the internal combustion engine, which causes a problem that the start of the exhaust purification system is delayed. . On the other hand, if the reducing agent is not recovered, the supply means may be damaged due to the freezing of the reducing agent as described above.

  The present invention has been made in view of the above problems, can suppress the supply means from being damaged due to freezing of the reducing agent, can suppress the reducing agent from solidifying in the supply means, and exhaust the exhaust. It is an object of the present invention to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress a delay in starting the purification system.

(First invention)
In order to solve the above problems, an exhaust gas purification apparatus for an internal combustion engine of the present invention is provided in an exhaust passage of the internal combustion engine, and a catalyst that purifies harmful components in the exhaust gas by supplying a reducing agent;
Supply means for supplying the liquid reducing agent stored in the storage section upstream of the catalyst in the exhaust passage;
A recovery means for recovering the reducing agent remaining in the supply means after the internal combustion engine is stopped in the storage unit;
The recovery means includes a pump that sucks back the reducing agent remaining in the supply means to the storage unit, and an operation of the pump when the reducing agent remaining in the supply means is completely sucked back to the storage unit. short working time than, characterized in that it comprises an actuation time control means for remaining in the supply means a predetermined amount of the reducing agent after the recovery to the reservoir by operating the pump.
(Second invention)
An exhaust gas purification apparatus for an internal combustion engine of the present invention is provided in an exhaust passage of the internal combustion engine, and a catalyst that purifies harmful components in exhaust gas by supplying a reducing agent;
Supply means for supplying the liquid reducing agent stored in the storage section upstream of the catalyst in the exhaust passage;
A recovery unit that once collects all the reducing agent remaining in the supply unit after the internal combustion engine is stopped in the storage unit, and then refills the supply unit with a predetermined amount of the reducing agent;
It is characterized by providing.

  In the present invention, the reducing agent remaining in the supply means is not completely recovered in the storage unit, but is recovered so that a predetermined amount of the reducing agent remains in the supply means. Thus, since the reducing agent remains in the supply means after collection in a form containing more water than when the reducing agent is completely recovered, the reducing agent is solidified in the supply means. Can be suppressed. Further, when the internal combustion engine is operated next time, the supply means is already filled with the predetermined amount of the reducing agent, so that the time until the supply means is completely filled with the reducing agent can be shortened. Therefore, it is possible to suppress a delay in starting the exhaust purification system. Further, since the reducing agent is collected, it is possible to suppress the supply means from being damaged due to the freezing of the reducing agent, compared to the case where no reducing agent is used.

It is a block diagram of the exhaust gas purification system of 1st Embodiment-3rd Embodiment. It is a flowchart of the urea water collection | recovery process of 1st Embodiment. It is the timing chart which expressed the operation state of each part relevant to urea water recovery processing on the time axis, and is the figure which contrasted each timing chart of complete sucking back, partial sucking back, and refilling. It is a flowchart of the urea water collection | recovery process of 2nd Embodiment. It is the timing chart which represented the operation state of each part relevant to the urea water recovery process of 3rd Embodiment on the time axis. It is a flowchart of the urea water collection | recovery process of 3rd Embodiment. It is a block diagram of the exhaust gas purification system of 4th Embodiment. It is a timing chart of 4th Embodiment, and is the figure which contrasted each timing chart of complete sucking back, partial sucking back, and refilling. It is a timing chart of 4th Embodiment, and is a timing chart in the case of opening an injector after delaying a refill start.

(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 100 mounted on a vehicle. The exhaust purification system 100 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 50 (hereinafter simply referred to as an engine) as an internal combustion engine. Has been built. In the exhaust purification system 100, the exhaust passage 12 is connected to the engine 50, and the exhaust from the engine 50 is discharged outside the vehicle through the exhaust passage 12.

The exhaust passage 12 is provided with an SCR catalyst 1 (NOx selective reduction catalyst) that selectively reduces NOx in the exhaust. The SCR catalyst 1 converts urea water (reducing agent) added from a urea water addition valve 2 described later into ammonia (NH3) by hydrolysis and stores the ammonia. Then, the SCR catalyst 1 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 formulas 1 and 2.
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 3H2O (Formula 2)

  The SCR catalyst 1 cannot store ammonia inexhaustably, and the maximum amount of ammonia that can be stored in the SCR catalyst 1 varies depending on the temperature of the SCR catalyst 1 (catalyst temperature). For example, when the catalyst temperature rapidly decreases, a phenomenon called ammonia slip in which ammonia is released from the SCR catalyst 1 occurs. Therefore, an oxidation catalyst 3 for purifying ammonia released from the SCR catalyst 1 by ammonia slip is provided downstream of the SCR catalyst 1 in the exhaust passage 12. The oxidation catalyst 3 has an oxidation function and decomposes ammonia into water and nitrogen.

  The exhaust purification system 100 is provided with a urea water supply system that supplies urea water upstream of the SCR catalyst 1 in the exhaust passage 12 in order to supply urea water to the SCR catalyst 1. Specifically, a urea water addition valve 2 for adding (supplying) urea water to the exhaust passage 12 is provided upstream of the SCR catalyst 1 in the exhaust passage 12. The urea water addition valve 2 has the same structure as a fuel injection valve that injects fuel into the cylinder of the engine 50. Specifically, the urea water addition valve 2 includes a drive unit composed of an electromagnetic solenoid or the like, and a valve main unit having a urea water passage through which urea water flows and a needle (sliding unit) for opening and closing a tip outlet. It is configured as an electromagnetic on-off valve provided and opens or closes based on a drive signal from the ECU 11. 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 urea water is added (injected) from the tip ejection port as the needle moves. Hereinafter, the urea water addition valve 2 is referred to as an injector.

  The urea water is sequentially supplied from the urea water tank 8 to the injector 2. The urea water tank 8 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration is stored therein. The urea water tank 8 and the injector 2 are connected by a pipe 13, and a urea water passage is formed in the pipe 13. A suction port for sucking urea water is formed at the tip of the pipe 13 on the urea water tank 8 side, and the urea water is stored in the urea water tank 8 in the state where the urea water is stored in the urea water tank 8. It is in an immersed state.

  A pump 7 is provided in the middle of the pipe 13. The pump 7 is an in-line electric pump (for example, a three-phase AC motor) that is rotationally driven by a drive signal from the ECU 11 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 8 and discharged to the injector 2 side through the pipe 13. On the other hand, the pump 7 is driven to rotate in the reverse direction (hereinafter referred to as reverse driving), so that the urea water filled in the injector 2 and the pipe 13 can be sucked back into the urea water tank 8 (recovery). It has become. In FIG. 1, the pump 7 is provided in a state of being immersed in the urea water in the urea water tank 8, but it may be provided outside the urea water tank 8.

  In the middle of the pipe 13, a porous urea water filter 4 for filtering urea water is provided. Foreign substances in the urea water are removed by the urea water filter 4 and foreign substances are prevented from entering the injector 2 and the urea water tank 8.

  A urea water pressure regulator 6 that adjusts the urea water addition pressure to be a predetermined pressure is provided on the downstream side (injector 2 side) of the pump 7. As a result of pressure adjustment by the urea water pressure regulator 6, surplus urea water is returned to the urea water tank 8. A urea water pressure sensor 5 that detects the pressure of the urea water in the pipe 13 is provided in the middle of the pipe 13. Instead of a method of mechanically controlling the urea water addition pressure with the urea water pressure regulator 6, a method of adjusting the urea water addition pressure by the ECU 11 controlling the drive of the pump 7 based on the detected value of the urea water pressure sensor 5. It may be adopted.

  The urea water supply system in which the injector 2, the pipe 13, the pump 7, the urea water pressure regulator 6, the urea water filter 4, and the urea water pressure sensor 5 described above supply urea water to the exhaust passage 12 (SCR catalyst 1) (the present invention). Corresponding to “supplying means”).

  Between the SCR catalyst 1 and the oxidation catalyst 3 in the exhaust passage 12, a NOx sensor 9 for detecting the NOx concentration in the exhaust gas that has passed through the SCR catalyst 1 is provided. An exhaust temperature sensor 10 that detects the exhaust temperature is provided upstream of the SCR catalyst 1 in the exhaust passage 12. The NOx sensor 9 and the exhaust temperature sensor 10 are used, for example, to control the amount of urea water added by the injector 2 and the addition timing.

  The exhaust purification system 100 includes an ECU 11. The ECU 11 includes a well-known microcomputer, and while the engine 50 is operating (ON), urea water is added to the exhaust passage 12 by the injector 2 based on detection values of various sensors (ureation time of urea water, (Addition amount) is controlled. The ECU 11 includes a timer 111 that measures time. The ECU 11 is connected to an ignition switch (IG switch) 14 that turns the engine 50 on and off.

  Further, the ECU 11 prevents the urea water supply system from being damaged by freezing of the urea water remaining in the urea water supply system including the injector 2, the pipe 13, and the like after the engine 50 is stopped. A urea water recovery process for recovering the urea water remaining in the supply system in the urea water tank 8 is executed. Hereinafter, details of the urea water recovery process will be described.

  FIG. 2 is a flowchart of urea water recovery processing executed by the ECU 11. FIG. 3 is a timing chart showing the operating state of each part related to the urea water recovery process on the time axis. 3, from the top, a timing chart of on / off of the engine 50 (ON / OFF of the IG switch 14), a timing chart according to a conventional method (“complete suck back”), and a method of this embodiment (“partial suck back”). ), And a timing chart according to a technique (“refilling”) of an embodiment described later. In the timing chart of each method of FIG. 3 (“complete suck back”, “partial suck back”, “refill”), the operating state of the pump 7 (on or off, In this case, the direction of rotation) indicates the operating state (open or closed) of the injector 2.

  The processing in FIG. 2 starts, for example, simultaneously with the start of the engine 50 (IG switch 14 is turned on). When the processing of FIG. 2 is started, the ECU 11 first determines whether or not the IG switch 14 (hereinafter simply referred to as IG) is turned off, that is, whether or not the engine 50 is stopped (S11). When the IG is on, that is, when the engine 50 is operating (S11: No), the process waits without proceeding to the subsequent processing. When the IG is on, the ECU 11 performs a process of supplying urea water to the exhaust passage 12 as necessary. When supplying the urea water, the ECU 11 normally rotates the pump 7 as shown in FIG. While driving, the injector 2 is opened.

  When the IG is off, that is, when the engine 50 is stopped (S11: Yes), the pump 7 is temporarily turned off (S12), and the urea water supply system (injector 2, piping 13 and the like) is performed in the processing after S13. The urea water filled in is recovered in the urea water tank 8. That is, the injector 2 is opened (S13), and the pump 7 is driven in reverse (S14). As a result, the urea water remaining in the urea water supply system flows to the urea water tank 8 side, and suction back (recovery) to the urea water tank 8 is started. Further, the ECU 11 starts measuring time by the timer 111 (see FIG. 1) simultaneously with the reverse rotation driving of the pump 7 (S14).

  Next, it is determined whether or not a predetermined time T2 has elapsed since the pump 7 was driven in reverse (S15). As shown in FIG. 3, the predetermined time T2 is longer than the time T1 for reversely driving the pump 7 when the urea water remaining in the urea water supply system is completely sucked back into the urea water tank 8 (complete suction back). It is set to a short time. That is, the ECU 11 does not completely suck the urea water back into the urea water tank 8 but intentionally leaves a part (predetermined amount) of the urea water in the urea water supply system.

  This residual amount of urea water is set to an amount that does not damage the urea water supply system even if urea water (residual urea water) remaining in the urea water supply system after sucking back expands due to freezing. Specifically, for example, when the residual urea water expands due to freezing, the amount of residual urea water is set so that an unfilled space equal to or larger than the expansion amount exists in the urea water supply system after sucking back. In other words, for example, when urea water expands, the volume increases by about 7% (see Patent Document 1). Therefore, even if the residual urea water expands by about 7%, the volume of the residual urea water after the expansion is the urea water supply system The amount of residual urea water is set so as to be less than the total volume (volume occupied by urea water when urea water supply system is completely filled with urea water). When the total volume in the urea water supply system cannot be accurately grasped, the volume of the pipe 13 may be used instead of the total volume in the urea water supply system.

  The amount of residual urea water is set to an amount that does not cause solidification of the residual urea water by drying. Specifically, the amount of residual urea water is set so that the amount of water in the residual urea water does not evaporate in consideration of the amount of saturated water vapor in the urea water supply system. More specifically, it can be seen from the saturated water vapor amount and humidity in the urea water supply system how much water can be evaporated. The amount of residual urea water is set so that the amount of water in the residual urea water is larger than the amount of water that can be evaporated. Thereby, it can suppress that the water | moisture content in residual urea water evaporates, As a result, it can suppress that residual urea water solidifies.

Note that the saturated water vapor amount and humidity in the urea water supply system actually vary depending on conditions such as temperature, but in order to prevent the configuration and processing from becoming complicated, they are set to predetermined fixed values here. . However, in order to obtain an accurate saturated water vapor amount, a temperature sensor for measuring the temperature in the urea water supply system is provided, and a predetermined saturated water vapor amount is corrected at the temperature measured by this temperature sensor, and the corrected saturation is obtained. The amount of residual urea water may be set based on the amount of water vapor. That is, the amount of residual urea water may be changed according to the temperature of the urea water supply system.

  Thus, the amount of residual urea water is larger than the amount of water that can evaporate, and the volume of residual urea water after expansion is less than the total volume in the urea water supply system. To be set. At this time, in order to refill urea water into the urea water supply system as soon as possible when the engine 50 is operated next time, the urea water supply system is not damaged by freezing of the residual urea water, and the residual urea water is dried. If the amount of residual urea water satisfies the condition of not solidifying, it is preferable that the amount of residual urea water is as large as possible.

  The predetermined time T2 in S15 is a time set in consideration of the capacity of the pump 7 and the like so that the amount of residual urea water becomes a predetermined amount determined in consideration of the expansion due to freezing and the saturated water vapor amount. If the predetermined time T2 has not yet elapsed (S15: No), the urea water sucking back is continued. When the predetermined time T2 has elapsed (S15: Yes), the pump 7 is turned off (S16), the injector 2 is closed (S17) (see also FIG. 3), and the processing of the flowchart of FIG. To do. The ECU 11 supplies the urea water to the exhaust passage 12 after the pump 7 is driven to rotate forward to refill the urea water into the urea water supply system when the engine 50 is operated next time.

  As described above, in the present embodiment, part of the urea water is intentionally left in the recovery of the urea water after the engine is stopped, so that the urea water is quickly supplied to the urea water supply system at the next engine operation. Can be refilled. Therefore, the delay of the exhaust purification system can be suppressed. In addition, since the amount of residual urea water is set in consideration of the amount of urea water expansion due to freezing and the amount of saturated water vapor, the urea water supply system (injector 2 and the like) can be prevented from being damaged and urea can be prevented. Problems such as clogging of the pipe 13 due to solidification of water and the sliding portion of the injector 2 sticking can be suppressed.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on the differences from the above embodiment. In the present embodiment, the urea water recovery process executed by the ECU 11 in FIG. 1 is different from that in the first embodiment, and other than that is the same as in the first embodiment. Hereinafter, the details of the urea water recovery process of this embodiment will be described.

  FIG. 4 is a flowchart of the urea water recovery process of this embodiment. The ECU 11 executes the process of FIG. 4 instead of the process of FIG. Further, the timing chart in the lower part of FIG. 3 (“refilling”) is a timing chart according to the process of FIG. In FIG. 4, the process of S21-S24 is the same as the process of S11-S14 of FIG. That is, the IG is turned off (S21: Yes), the pump 7 is turned off once (S22), the injector 2 is opened (S23), the pump 7 is driven in reverse (S24), and the urea water is sucked back. To start.

  Next, it is determined whether or not a predetermined time T1 has elapsed since the start of sucking back urea water (S25). The predetermined time T1 is the same as the suck back time T1 in the “complete suck back” in the upper part of FIG. That is, in this embodiment, the urea water remaining in the urea water supply system is once sucked completely back into the urea water tank 8. If the predetermined time T1 has not yet elapsed (S25: No), the urea water sucking back is continued. When the predetermined time T1 has elapsed, that is, when the urea water is once completely sucked back (S25: Yes), the pump 7 is driven to rotate forward so that the urea water in the urea water tank 8 is supplied to the urea water supply system. Refill (S26). At this time, as shown in FIG. 3, the injector 2 is opened from the beginning of refilling. Further, the timer 111 measures the time from the start of refilling.

  Next, it is determined whether or not a predetermined time T4 has elapsed since the start of refilling (S27). The predetermined time T4 is set to a time shorter than the time T3 for driving the pump 7 in the normal rotation when the urea water supply system is completely filled with urea water (complete filling). Specifically, the predetermined time T4 is set in consideration of the capacity of the pump 7 and the like so that the amount of urea water charged by refilling is the same as the amount of residual urea water in the first embodiment. It's time.

  If the predetermined time T4 has not yet elapsed (S27: No), the urea water refilling is continued. When the predetermined time T4 has elapsed (S27: Yes), the pump 7 is turned off (S28), the injector 2 is closed (S29), and refilling is terminated. Then, the process of the flowchart of FIG. 4 is complete | finished.

  As described above, according to the present embodiment, in addition to the effects of the above-described embodiment, the air in the pipe 13 is pushed out to the injector 2 side at the time of refilling in S26. The urea water adhering to the moving part can be discharged outside. Thereby, solidification (urea precipitation) of urea water at the sliding portion of the injector 2 can be further suppressed.

(Third embodiment)
Next, a third embodiment of the present invention will be described focusing on the differences from the above embodiment. In the present embodiment, the urea water recovery process executed by the ECU 11 in FIG. 1 is different from those in the first and second embodiments, and other than that is the same as in the first and second embodiments. This embodiment is a modification of the second embodiment. Specifically, as shown in the timing chart of FIG. 5, the valve opening of the injector is refilled after the urea water is completely sucked back once. The timing is delayed from the refill start timing (the pump normal rotation drive start timing). Note that the times T1 and T4 in FIG. 5 are the same as the times T1 and T4 in FIG. Hereinafter, the details of the urea water recovery process of this embodiment will be described.

  FIG. 6 is a flowchart of the urea water recovery process executed by the ECU 11 (see FIG. 1) of the present embodiment. ECU11 performs the process of FIG. 6 instead of the process of FIG. 2, FIG. In FIG. 6, the same processes as those in FIG. 4 are denoted by the same reference numerals. The process of FIG. 6 is different from the process of FIG. 4 in that the processes of S261 to S263 are added between the processes of S26 and S27, and the other processes are the same as those of FIG.

  That is, the injector 2 is closed at the start of refilling of the urea water (at the time of processing of S26) (S261). The closing timing of the injector 2 may be simultaneous with the start of refilling of urea water (simultaneously with the process of S26) or before the start of refilling of urea water (before the process of S26).

  Next, it is determined whether or not a predetermined time T5 has elapsed since the start of refilling (S262). The predetermined time T5 may be shorter than the predetermined time T4 (refill end time) as shown in FIG. 5, or may be the same time as the predetermined time T4. However, the predetermined time T5 is preferably closer to the predetermined time T4 in that the urea water in the injector 2 is blown off more strongly when the injector 2 is subsequently opened. When the predetermined time T5 and the predetermined time T4 are the same time, the process of S27 may be omitted.

  If the predetermined time T5 has not yet elapsed (S262: No), the valve closing of the injector 2 is continued. When the predetermined time T5 has elapsed (S262: Yes), the injector 2 is opened (S263). Thereafter, when the predetermined time T4 has elapsed (S27: Yes), the pump 7 is turned off (S28), the injector 2 is closed (S29), and refilling is terminated. Thereafter, the process of the flowchart of FIG.

  Thus, in this embodiment, since the injector 2 is closed for a while from the start of refilling, the pressure in the urea water supply system (the piping 13, the injector 2, etc.) increases, and the valve opening of the injector 2 thereafter is opened. At times, this pressure can blow the urea water in the injector 2 to the outside. Therefore, in this embodiment, solidification of urea water (urea precipitation) at the sliding portion of the injector 2 can be further suppressed in addition to the effects of the above embodiment.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described focusing on the differences from the above embodiment. FIG. 7 is a configuration diagram of the exhaust purification system 101 of the present embodiment. In FIG. 7, the same components as those in the exhaust purification system 100 of FIG. The exhaust purification system 101 of FIG. 7 is different from the configuration of FIG. 1 in that a pump 71 and a flow path switching valve 72 are provided instead of the rotary pump 7 of FIG. Is the same.

  The pump 71 is a pump having a function of pumping a fluid only in one direction P1 (see FIG. 7) like a pumping pump. That is, the pump 71 includes an inlet 711 through which fluid flows into the pump 71 and an outlet 712 through which fluid flows out of the pump 71. And the pump 71 pumps the fluid which entered from the inflow port 711 to the direction P1, and makes it flow out from the outflow port 712. As described above, the urea water cannot be sucked back into the urea water tank 8 by the pump 71 alone. The pump 71 is provided in the middle of the pipe 13.

  The flow path switching valve 72 is provided in the middle of the pipe 13. Specifically, the flow path switching valve 72 includes an inlet 711 and an outlet 712 of the pump 7, an end 133 (hereinafter referred to as a tank side pipe) of the pipe 13 on the urea water tank 8 side, and a pipe 13 on the injector 2 side. Are connected to each of the end portions 134 (hereinafter referred to as injector-side piping).

  The flow path switching valve 72 is a valve that switches a flow path through which urea water in the pipe 13 flows based on a switching signal from the ECU 11. Specifically, the flow path switching valve 72 includes a first flow path state in which the tank side pipe 133 and the inflow port 711 are connected, and the injector side pipe 134 and the outflow port 712 are connected, and the injector side pipe 134. Is a valve that switches the flow path between the second flow path state in which the tank-side pipe 133 and the outlet 712 are connected. In FIG. 7, in the flow path switching valve 72, the first flow path state is indicated by a solid line, and the second flow path state is indicated by a dotted line.

  When the flow path switching valve 72 is in the first flow path state, the urea water flows in the pipe 13 from the urea water tank 8 toward the injector 2 by the operation of the pump 71. On the other hand, when the flow path switching valve 72 is in the second flow path state, the urea water flows in the pipe 13 from the injector 2 to the urea water tank 8 by the operation of the pump 71.

  The ECU 11 controls the flow path switching by the flow path switching valve 72, thereby supplying urea water from the injector 2 to the exhaust passage 12 when the engine 50 is operating, and urea water to the urea water tank 8 when the engine 50 is stopped. Collect (suck back). Here, FIG. 8 shows a timing chart in which the operation state of each part related to urea water recovery in the present embodiment is represented on the time axis. The timing chart of FIG. 8 corresponds to the timing chart of FIG. 3. From the top, the engine 50 (IG) is turned on / off, the timing chart according to the conventional method (“complete suck back”), and the same as in the first embodiment. 6 shows a timing chart by the method (“partial suck back”) and a timing chart by the same method (“refilling”) as in the second embodiment. Moreover, in the timing chart of each method of FIG. 8, from the top, the operating state of the pump 71 (whether it is turned on or off), the state of the flow path switching valve 72, and the operating state of the injector 2 (open or closed) Or). In the timing chart of the flow path switching valve 72 in FIG. 8, the first flow path state is “flow path: normal”, and the second flow path state is “flow path: reverse”. In FIG. 8, times T1, T2, and T4 are the same as times T1, T2, and T4 in FIG. 3, respectively.

  As shown in FIG. 8, when the IG is on, the ECU 11 turns on the pump 71, sets the flow path switching valve 72 to the first flow path state (flow path: positive), and opens the injector 2. By doing so, the urea water is supplied to the exhaust passage 12.

  On the other hand, when the IG is turned off, the ECU 11 collects the urea water remaining in the urea water supply system (injector 2, pipe 13, etc.) in the urea water tank 8 as in the above embodiment, and at this time, intentionally A fixed amount of urea water is left in the urea water supply system. Specifically, when collecting “partial suck back” in FIG. 8, the ECU 11 drives the pump 71 for a predetermined time T2 shorter than the time T1 due to complete suck back, and the predetermined time. During T2, the flow path switching valve 72 is set to the second flow path state (flow path: reverse). In this case, a process of “switching the flow path switching valve to the second flow path state” may be added instead of the process of S14 in FIG. As a result, the same effect as in the first embodiment can be obtained.

  Further, when performing the “refill” recovery of FIG. 8, the ECU 11 first drives the pump 71 for a predetermined time T1, and changes the state of the flow path switching valve 72 to the second for the predetermined time T1. By setting the flow path state, the urea water is once completely sucked back into the urea water tank 8. Thereafter, the ECU 11 drives the pump 71 for a predetermined time T4 and supplies the urea water by a predetermined amount by setting the flow path switching valve 72 to the first flow path state for the predetermined time T4. Refill the system. In addition, the injector 2 is opened from the start of refilling. In this case, in FIG. 4, instead of the process of S24, a process of “switching the flow path switching valve to the second flow path state” is added, and instead of the process of S26, What is necessary is just to add the process "switching to 1 flow path state". As a result, the same effect as in the second embodiment can be obtained.

  Further, FIG. 9 shows a timing chart by the same method (“refilling”) as in the third embodiment. The ECU 11 controls the pump 71 and the flow path switching valve 72 in the same manner as in the “refilling” in FIG. 8 when the “refilling” in FIG. On the other hand, the valve is closed for a while from the start of refilling (until the predetermined time T5 elapses), and is opened after the predetermined time T5 elapses. In this case, in FIG. 6, in place of the process of S24, a process of “switching the flow path switching valve to the second flow path state” is added, and instead of the process of S26, What is necessary is just to add the process "switching to 1 flow path state". Thereby, the same effect as that of the third embodiment can be obtained.

  As described above, even when a pump having a function of pumping fluid in only one direction is used, the same effect as that of the above embodiment can be obtained by using the flow path switching valve.

  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 third embodiment and the fourth embodiment, the injector 2 is opened after a predetermined time T5 has elapsed at the time of refilling. However, when the pressure detected by the urea water pressure sensor 5 exceeds the predetermined pressure, the injector 2 is opened. The valve may be opened. This also allows the urea water in the injector 2 to be blown out by high pressure when the injector 2 is opened. 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).

1 SCR catalyst 2 Urea water addition valve (injector)
8 Urea water tank 7, 71 Pump 72 Flow path switching valve 11 ECU
12 Exhaust passage 13 Piping 50 Diesel engine (internal combustion engine)
100, 101 Exhaust purification system

Claims (9)

A catalyst (1) provided in the exhaust passage (12) of the internal combustion engine (50) and purifying harmful components in the exhaust gas by supplying a reducing agent;
Supply means (2, 13, 7, 4, 5, 6) for supplying the liquid reducing agent stored in the storage section (8) upstream of the catalyst in the exhaust passage;
Recovery means (11, 7, 71, 72) for recovering the reducing agent remaining in the supply means after the internal combustion engine is stopped in the storage unit;
The recovery means includes a pump (7, 71) for sucking the reducing agent remaining in the supply means back into the storage unit, and a case where the reducing agent remaining in the supply means is completely sucked back into the storage unit. Operating time control means (S14 to S16, 11) that causes a predetermined amount of the reducing agent to remain in the supply means after recovery to the storage unit by operating the pump for an operating time shorter than the operating time of the pump in ), An exhaust gas purification apparatus for an internal combustion engine (100, 101).   A catalyst (1) provided in the exhaust passage (12) of the internal combustion engine (50) and purifying harmful components in the exhaust gas by supplying a reducing agent;
  Supply means (2, 13, 7, 4, 5, 6) for supplying the liquid reducing agent stored in the storage section (8) upstream of the catalyst in the exhaust passage;
  After all the reducing agent remaining in the supply unit after the internal combustion engine is stopped is once recovered in the storage unit, a recovery unit (11, 7) for refilling the supply unit with a predetermined amount of the reducing agent. 71, 72),
  An exhaust emission control device (100, 101) for an internal combustion engine, comprising:   The predetermined amount is an amount that does not damage the supply means even if the residual reducing agent remaining in the supply means after the recovery expands due to freezing, and the moisture of the residual reducing agent evaporates. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas purification device is an amount that is not cut off.   4. The internal combustion engine according to claim 3, wherein the predetermined amount is determined so that an unfilled space equal to or larger than an expansion due to freezing of the residual reducing agent exists in the supply means after the recovery. Exhaust purification equipment.   5. The predetermined amount is defined so that the water content of the residual reducing agent is larger than a water content that can be evaporated based on a saturated water vapor amount in the supply means. An exhaust gas purification apparatus for an internal combustion engine as described. The supply means includes an addition valve (2) for supplying the reducing agent to the exhaust passage,
The recovery means includes valve control means (11) for controlling to open the addition valve at the time of refilling, and the valve control means (S261, S262, S263) is for opening the addition valve. The exhaust gas purification apparatus for an internal combustion engine according to claim 2 , wherein the timing is delayed from the start timing of the recharging. The supply means includes an addition valve (2) for supplying the reducing agent to the exhaust passage, a pipe (13) connecting between the storage unit and the addition valve, and the reducing agent stored in the storage unit. And a pump (7) for feeding through the pipe to the addition valve,
The pump is configured to be switchable between an operation direction in which the reducing agent is fed from the storage unit toward the addition valve and an operation direction in which the reducing agent is fed from the addition valve toward the storage unit. And
The said collection | recovery means is equipped with the said pump and the pump control means (11) which performs the said collection | recovery by controlling the operating direction of the said pump, The any one of Claims 1-6 characterized by the above-mentioned. An exhaust purification device for an internal combustion engine. The supply means includes an addition valve (2) for supplying the reducing agent to the exhaust passage, a pipe (13) connecting between the storage unit and the addition valve, and the reducing agent stored in the storage unit. A pump (71) for feeding the gas to the addition valve through the pipe,
The operating direction of the pump is only one direction,
The recovery means includes a flow path for the reducing agent in the pump and the supply means, and a flow path for the reducing agent to flow from the storage section toward the addition valve and from the addition valve to the storage section. A switching unit (72) for switching between the flow path through which the reducing agent flows, and a switching control unit (11) for performing the recovery by controlling the switching of the flow path by the switching unit. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6. The reducing agent is urea water;
9. The NOx selective reduction catalyst according to claim 1, wherein the catalyst is a NOx selective reduction catalyst that reduces NOx in exhaust gas with ammonia generated from urea water supplied from the supply unit. 10. An exhaust purification device for an internal combustion engine.

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