JP2015232295A - Internal combustion engine exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a quantity of urea water remaining in an addition valve while suppressing the entry of foreign objects in the addition valve in a urea SCR system.SOLUTION: An SCR catalyst 4 is disposed in an exhaust passage 3 of an engine 2, and an addition valve 5 adding urea water to the exhaust passage 3 is disposed upstream of the SCR catalyst 4. The urea water is stored in a urea water tank 6, and a pump 7 supplying the urea water from the urea water tank 6 to the addition valve 5 is provided. A branch pipe 10 is connected to a pipe 8 forming a channel between the addition valve 5 and the urea tank 6. A check valve 13 is disposed in a channel of the branch pipe 10. If a condition that the engine 2 is stopped and the pump 7 is stopped is satisfied, a DCU 19 opens the addition valve 5 to add the urea water to the exhaust passage 3 by a residual pressure in the addition valve 5. In the addition process, valve opening time and the number of times of valve opening are adjusted to reduce the residual pressure (residual urea water) in the addition valve 5. Subsequently, the pump 7 is driven to rotate reversely to attract the urea water remaining in the pump 7 back to the urea water tank 6.

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). . Patent Document 1 describes that an addition valve is opened in order to introduce air into a urea water supply system when urea water is sucked back.

JP 2008-101564 A

  However, if the liquid (urea water) is sucked back with the addition valve opened, foreign matter present in the exhaust passage may be sucked into the addition valve, and the function of the addition valve is reduced by the foreign matter. There is a problem.

  The present invention has been made in view of the above problems, and provides an exhaust emission control device for an internal combustion engine that can reduce the amount of liquid remaining in the addition valve while suppressing foreign matter from entering the addition valve. Is an issue.

In order to solve the above problems, an exhaust gas purification apparatus for an internal combustion engine of the present invention includes a tank in which a liquid for purifying harmful substances in 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;
A pump for supplying the liquid stored in the tank to the addition valve through the pipe when the internal combustion engine is operated;
After the internal combustion engine is stopped, an addition control means for adding the liquid remaining in the addition valve by opening the addition valve without supplying and sucking the liquid to the addition valve;
It is characterized by providing.

  According to the present invention, after the internal combustion engine is stopped, the addition valve is opened without supplying or sucking back the liquid to the addition valve, so that the urea water is exhausted by the residual pressure of the urea water remaining in the addition valve. It can be discharged (added) into the passage. Therefore, it is possible to reduce the amount of liquid remaining in the addition valve while suppressing foreign matters from entering the addition valve.

It is a block diagram of the exhaust gas purification system in 1st, 2nd embodiment. It is sectional drawing which showed the whole structure of the addition valve. It is the A section enlarged view of FIG. It is a flowchart of the exclusion process of 1st Embodiment. It is a flowchart of the exclusion process of 2nd Embodiment. It is a block diagram of the exhaust gas purification system in 3rd-6th embodiment. It is the B section enlarged view of FIG. It is a flowchart of the exclusion process of 3rd Embodiment. It is a flowchart of the exclusion process of 4th Embodiment. It is a flowchart of the exclusion process of 5th Embodiment. It is a flowchart of the exclusion process of 6th Embodiment.

(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.

  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. In this embodiment, the branch pipe 10 is connected in the vicinity of the urea water tank 6 and the pump 7, but may be connected to any position of the pipe 8 from the addition valve 5 to the pump 7.

  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 branch pipe 10 to the pipe 8 and prohibits fluid from flowing from the pipe 8 to the branch pipe 10. 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. In this embodiment, the upstream side of the check valve 13 is open (no connection). However, the check valve 13 is provided in a space part such as a space part in the urea water tank 6 separated from the outside by a partition wall. The upstream side may be connected. As a result, it is possible to introduce air into the pipe 8 with less contamination of foreign matters such as water.

  A pressure sensor 14 that detects the pressure in the addition valve side pipe 81 is provided on the addition valve 5 side pipe 81 (addition valve side pipe) from the connection portion between the branch pipe 10 and the pipe 8. 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). Further, the DCU 19 controls the driving of the pump 7. Specifically, when the urea water is added by the addition valve 5 when the engine 2 is operated, the pump 7 is driven to rotate forward so that the addition valve is fed from the urea water tank 6. 5 is supplied with urea water.

  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. In addition, it is necessary to avoid contamination of the addition valve 5 with foreign matter. 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 executes a process (exclusion process) for removing urea water remaining in the urea water supply system after the engine 2 is stopped. The details of this exclusion process will be described below. FIG. 4 is a flowchart of the exclusion process. The process of FIG. 4 is repeatedly executed at predetermined time intervals while the DCU 19 is operating.

  When the processing of FIG. 4 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 residual urea water exclusion control is satisfied. Is determined (S1). 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 (S1: No), the processing of FIG. In this case, urea water exclusion control (residual pressure injection control, suck back control) is not executed.

  On the other hand, when both stop of the engine 2 and stop of the pump 7 are established (S1: Yes), an energization signal is output to the addition valve 5 to perform valve opening control (residual pressure injection control). Perform (S2). As a result, the urea water is injected (added) from the tip outlet 62 of the addition valve 5 into the exhaust passage 3 by the residual pressure of the urea water remaining in the addition valve 5 and the pipe 8 in the vicinity of the addition valve 5. Can do. At this time, the addition valve 5 is opened, but since the pump 7 is stopped, the air suction force from the exhaust passage 3 into the addition valve 5 does not work. Therefore, it can suppress that the foreign material which exists in the exhaust passage 3 mixes in the addition valve 5, and the functional fall of the addition valve 5 can be avoided.

  As the residual pressure injection control of S2, the DCU 19 opens the addition valve 5 once by one residual pressure injection control (addition control), for example, by outputting a continuous energization signal to the addition valve 5 for a predetermined time. Execute the continuous addition control to be valved. In this continuous addition control, the valve opening time (injection time) of the addition valve 5 is a control parameter for the addition valve 5. In the present embodiment, the valve opening time of the addition valve 5 in the continuous addition control is set so that the residual pressure in the addition valve 5 after the continuous addition control is less than a predetermined pressure, in other words, in the addition valve 5 after the continuous addition control. In the addition valve 5, a time set in advance is set so that urea water does not remain in the addition valve 5, or even if it remains, there is a space in the addition valve 5 that can absorb the expansion volume when the urea water expands due to freezing. . By adding urea water by continuous addition control, the residual pressure (residual urea water) in the addition valve 5 can be lowered in a shorter period of time compared to intermittent addition control described later.

  The DCU 19 outputs an intermittent energization signal (an energization signal that alternately turns on and off alternately) to the addition valve 5 instead of the continuous addition control, thereby performing a single residual pressure injection control (addition control). Intermittent addition control that alternately repeats opening and closing of the addition valve may be executed. In this intermittent addition control, the valve opening time of the addition valve 5 (pulse width of the energization signal) (injection time) and the number of valve openings (number of injections) are the control parameters of the addition valve 5. In this embodiment, when executing intermittent addition control, the valve opening time and the number of times of valve opening in the intermittent addition control are paraphrased so that the residual pressure in the addition valve 5 after the intermittent addition control is less than a predetermined pressure. And so that urea water does not remain in the addition valve 5 after intermittent addition control, or even if it remains, there is a space in the addition valve 5 that can absorb the expansion volume when the urea water expands due to freezing. The value is set in advance by experiment or calculation. According to the intermittent addition control, the needle 56 (see FIG. 2) of the addition valve 5 frequently moves up and down, so that the residual urea water can be effectively pushed out of the addition valve 5 by the movement. That is, the residual pressure in the addition valve 5 can be reduced more reliably.

  After executing the residual pressure injection control, the DCU 19 reversely drives the pump 7 to suck the urea water remaining in the urea water supply system back into the urea water tank 6 (S3). When the pump 7 is driven in reverse, the check valve 13 is opened by the negative pressure in the pipe 8, and air is introduced into the pipe 8 from the branch pipe 10. The introduced air circulates in the pipe 82 (tank side pipe) and the pump 7 (main body 71) on the urea water tank 6 side (pump 7 side) from the connection part between the branch pipe 10 and the pipe 8, Residual urea water in the tank side pipe 82 and the pump 7 can be driven out. The residual urea water expelled by the air is discharged to the urea water tank 6 through the suction port 72 (in this case, functioning as a discharge port).

  Further, in the suck back control in S3, the addition valve 5 is kept closed. As a result, it is possible to prevent foreign matter from entering the addition valve 5 from the exhaust passage 3. In the suction back control, the residual urea water in the addition valve side pipe 81 and the addition valve 5 is not sucked back, but since the residual urea water is added to the exhaust passage 3 in S2, S2, S3 Thus, the remaining urea water in the entire urea water supply system can be reduced.

  The suck back control is executed for a predetermined time. This predetermined time is set so that the urea water does not remain in the tank side pipe 82 and the pump 7 (particularly in the pump 7) after the suck back control is performed, or the urea water expands due to freezing even if it remains. It is set so that a space capable of absorbing the expanded volume exists in the pump 7. After executing the suck back control, the process of the flowchart of FIG. 4 is terminated.

  As described above, according to the present embodiment, since the addition valve 5 is opened with the pump 7 stopped, the residual urea water in the addition valve 5 can be added by the residual pressure, and the addition valve 5 It is possible to suppress the entry of foreign matter. Further, the residual urea water in the pump 7 can be sucked back into the urea water tank 6 by the suction back control.

  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 back flow of urea water or air can be prevented from the pipe 8 to the check valve 13 side.

  In the exclusion control of FIG. 4, the suction back control is executed after the residual pressure injection control is executed. However, the suction back control may be executed before the residual pressure injection control is executed. That is, the process of S2 and the process of S3 may be interchanged.

(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. Exclusion processing 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 exclusion process shown in FIG. Details of the exclusion process of FIG. 5 will be described below. 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 exclusion control is satisfied. Is determined (S4). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S4: No), the process of FIG. 5 is terminated.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S4: Yes), the urea water pressure P (pressure in the addition valve side pipe 81) detected by the pressure sensor 14 (see FIG. 1). Is read (S5). This urea water pressure P corresponds to the residual pressure in the addition valve 5. Next, it is determined whether the urea water pressure P is higher than a predetermined pressure (S6). This predetermined pressure is an upper limit of a pressure that is low enough not to damage the addition valve 5 even if the residual urea water expands due to freezing. When the urea water pressure P is lower than the predetermined pressure (S6: No), the suction back control similar to S3 in FIG. 4 is executed (S10). Thereby, the residual urea water in the urea water supply system (particularly the tank side pipe 82 and the pump 7) can be sucked back into the urea water tank 6. Further, since the residual pressure in the addition valve 5 is originally low, there is no problem even if the urea water is not excluded from the addition valve 5. After executing the suck back control, the process of the flowchart of FIG. 5 is terminated.

  On the other hand, if the urea water pressure P is higher than the predetermined pressure in S6 (S6: Yes), the residual pressure injection control similar to S2 in FIG. 4 is executed (S7). At this time, the control parameter of the addition valve 5 in the residual pressure injection control is set according to the value of the urea water pressure P read immediately before. Specifically, when the continuous addition control is executed as the residual pressure injection control, the valve opening time of the addition valve 5 is increased as the urea water pressure P is higher. Further, when intermittent addition control is executed as the residual pressure injection control, as the urea water pressure P is higher, at least one of the valve opening time (pulse width of the energization signal) of the addition valve 5 and the number of times of valve opening is increased. For example, a relationship (map) between the urea water pressure P and the valve opening time or the number of times of valve opening is stored in advance in a memory in the DCU 19, and the valve opening time corresponding to the current urea water pressure P based on this relationship. Alternatively, the value of the number of valve openings may be determined.

  Thus, by setting the control parameter of the addition valve 5 according to the value of the urea water pressure P, the residual pressure (residual urea water) in the addition valve 5 can be efficiently reduced.

  Thereafter, the urea water pressure P is read again from the pressure sensor 14 (S8), and it is determined whether or not the urea water pressure P has become lower than a predetermined pressure (S9). Similarly to the predetermined pressure in S6, this predetermined pressure is also an upper limit of a pressure that is low enough not to damage the addition valve 5 even if the residual urea water expands due to freezing. When the urea water pressure P is still higher than the predetermined pressure (S9: No), the process returns to S7, the control parameter of the addition valve 5 is reset based on the urea water pressure P read immediately before, and the control parameter Residual pressure injection control is executed again (S7).

  When the urea water pressure P becomes lower than the predetermined pressure in S9 (S9: Yes), the suction back control is executed (S10), and the process of the flowchart of FIG.

  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 residual pressure injection control is executed until the urea water pressure P becomes less than the predetermined pressure, the residual urea water in the addition valve 5 can be reliably reduced. Further, when the urea water pressure P is originally less than the predetermined pressure, the execution of the residual pressure injection control is stopped, so that the processing can be simplified.

  In the exclusion control of FIG. 5, the suck back control is executed after the residual pressure injection control is executed. However, the suck back control may be executed before the residual pressure injection control is executed. Specifically, the suck back control in S10 may be executed before the process in S5.

(Third embodiment)
Next, a third embodiment of the present invention will be described focusing on the differences from the above embodiment. FIG. 6 is a configuration diagram of the exhaust purification system of the present embodiment. In the exhaust purification system 1a of FIG. 6, the same components as those of the exhaust purification system 1 of FIG. The configuration of the exhaust gas purification system 1a is different from the exhaust gas purification system 1 of FIG. is there.

  Here, FIG. 7 is an enlarged view of part B of FIG. As shown in FIG. 7, the three-way valve 9 includes an opening / closing part 91 connected to the branch pipe 10 and the 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. 7 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 position C, the flow path of the branch pipe 10 is closed, and the flow path of the addition valve side pipe 81 and the flow path of the tank side pipe 82 are opened. 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 DCU 19 performs switching control of the three-way valve 9. Specifically, when urea water is added by the addition valve 5 when the engine 2 is operated, the three-way valve 9 is placed in the first flow path state (position C in FIG. 7). 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 reliably prevented from flowing into the branch pipe 10, and air and foreign matter are introduced into the pipe 8 from the branch pipe 10. 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.

  Further, the exclusion process executed by the DCU 19 is different from the above embodiment. Specifically, the DCU 19 executes the exclusion process shown in FIG. Details of the exclusion process of FIG. 8 will be described below. 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 exclusion control is satisfied. Is determined (S11). If neither the stop of the engine 2 nor the stop of the pump 7 is established (S11: 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 (S11: Yes), the three-way valve 9 is switched to the second flow path state (the state at the position D in FIG. 7) (S12). Thereafter, residual pressure injection control and suck back control are executed (S13, S14). The residual pressure injection control in S13 is the same as the residual pressure injection control in S2 of FIG. Further, the suck back control in S14 is the same as the suck back control in S3 of FIG. Thereafter, the DCU 19 switches the three-way valve 9 from the second flow path state to the first flow path state at the timing when the suck back control is finished or at the timing when the engine 2 is started.

  Thus, according to the present embodiment, in addition to the same effects as those of the above-described embodiment, urea water can be used in a state where the three-way valve 9 is switched to the second flow path state and the flow path of the addition valve side pipe 81 is closed. Since the residual pressure injection and the suction back are performed, it is possible to prevent foreign matters from entering the addition valve side pipe 81 and the addition valve 5 side from the pump 7 and the branch pipe 10 side. Further, by closing the addition valve side pipe 81, it is possible to avoid the residual pressure in the addition valve side pipe 81 and the addition valve 5 from flowing (escape) to the pump 7 side during the residual pressure injection control. Residual pressure injection can be performed effectively. 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 during the suck back control. As a result, the air remains in the tank side pipe 82 and the pump 7. The urea water that has been used can be sucked back efficiently. Therefore, damage to the pump 7 can be effectively suppressed.

  In the exclusion control of FIG. 8, the suction back control is executed after the residual pressure injection control is executed. However, the suction back control may be executed before the residual pressure injection control is executed. That is, the suck back control in S14 may be executed before the process in S13. In the exclusion control of FIG. 8, the three-way valve 9 is switched to the second flow path state before the process of S13. However, after the process of S13, the three-way valve 9 is set to the second flow before the process of S14. You may switch to a flow path state. Also by this, it can suppress that a foreign material mixes into the addition valve 5 side from the pump 7 and the branch pipe 10 side in the case of suck-back control.

(Fourth embodiment)
Next, a fourth 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. Exclusion processing executed by the DCU 19 is different from that of the third embodiment, and other than that is the same as that of the third embodiment. The DCU 19 executes the exclusion process shown in FIG. Details of the exclusion process of FIG. 9 will be described below. 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 exclusion control is satisfied. Is determined (S15). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S15: 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 (S15: Yes), the three-way valve 9 is switched to the second flow path state (the state of the position D in FIG. 7) (S16). Next, the pump 7 is driven in reverse to start sucking back urea water (S17). During the suction back, the residual pressure injection control similar to S2 in FIG. 4 is executed (S18). Thereafter, the pump 7 is stopped, the suck back control is ended (S19), and the processing of the flowchart of FIG. 9 is ended.

  Thus, according to this embodiment, in addition to the same effect as the above embodiment, the three-way valve 9 is switched to the second flow path state, and the flow path of the addition valve side pipe 81 is closed. Residual pressure injection control can be performed during the suction back control (while the pump 7 is operating). That is, the suction back control and the residual pressure injection control can be executed simultaneously. Therefore, residual urea water in the urea supply system can be eliminated in a short time.

(Fifth embodiment)
Next, a fifth 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. Exclusion processing executed by the DCU 19 is different from the third and fourth embodiments, and other than that is the same as the third and fourth embodiments. The DCU 19 executes the exclusion process shown in FIG. Details of the exclusion process of FIG. 10 will be described below. The process of FIG. 10 is repeatedly executed at predetermined time intervals while the DCU 19 is operating.

  When the processing of FIG. 10 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 exclusion control is satisfied. Is determined (S20). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S20: No), the process of FIG. 10 is terminated.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S20: Yes), the three-way valve 9 is switched to the second flow path state (position D in FIG. 7) (S21). Thereafter, similarly to the second embodiment (S5 to S9 in FIG. 5), the residual pressure injection control is executed until the urea water pressure P detected by the pressure sensor 14 becomes less than a predetermined pressure (S22 to S26). Thereafter, the suck back control similar to that in the above embodiment is executed while maintaining the three-way valve 9 in the second flow path state (S27).

  As described above, according to the present embodiment, the three-way valve 9 is switched to the second flow path state, and the residual pressure injection and sucking back of the urea water are executed. Therefore, as in the third and fourth embodiments. The effect of can be obtained. Further, since the residual pressure injection control is executed based on the urea water pressure P, the same effect as in the second embodiment can be obtained.

  In the exclusion control of FIG. 10, the suction back control is executed after the residual pressure injection control is executed. However, the suction back control may be executed before the residual pressure injection control is executed. Specifically, the suck back control in S27 may be executed before the process in S22. In the exclusion control of FIG. 10, the three-way valve 9 is switched to the second flow path state before the process of S22. However, after the process of S26, the three-way valve 9 is set to the second flow before the process of S27. You may switch to a flow path state. Also by this, it can suppress that a foreign material mixes into the addition valve 5 side from the pump 7 and the branch pipe 10 side in the case of suck-back control.

(Sixth embodiment)
Next, a sixth 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. Exclusion processing executed by the DCU 19 is different from the third to fifth embodiments, and other than that is the same as the third to fifth embodiments. The DCU 19 executes the exclusion process shown in FIG. Hereinafter, details of the exclusion process of FIG. 11 will be described. The process of FIG. 11 is repeatedly executed at predetermined time intervals while the DCU 19 is operating.

  When the processing of FIG. 11 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 exclusion control is satisfied. Is determined (S28). When neither the stop of the engine 2 nor the stop of the pump 7 is established (S28: No), the process of FIG. 11 is terminated.

  On the other hand, when both the stop of the engine 2 and the stop of the pump 7 are established (S28: Yes), the three-way valve 9 is switched to the second flow path state (position D in FIG. 7) (S29). Next, the pump 7 is driven in reverse to start sucking back urea water (S30). During the sucking back, the residual pressure injection control is executed until the urea water pressure P becomes less than the predetermined pressure (S31 to S35), as in the second embodiment (S5 to S9 in FIG. 5). Thereafter, the pump 7 is stopped, the suck back control is ended (S36), and the processing of the flowchart of FIG. 11 is ended.

  As described above, according to the present embodiment, the suction back control and the residual pressure injection control are executed simultaneously as in the fourth embodiment, so that the residual urea water in the urea supply system can be eliminated in a short period of time. it can. Further, since the residual pressure injection control is executed based on the urea water pressure P, the same effect as in the second embodiment can be obtained.

  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 said 3rd-6th 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 piping (addition valve) on the addition valve side rather than a connection part An open / close valve (for example, a shutter valve) that opens and closes the flow path may be provided at any position of the side pipe. In this case, when adding urea water with the addition valve during engine operation, the on-off valve is opened and the addition valve side pipe is opened. In contrast, when urea water is sucked back or residual pressure is injected (specifically, instead of the “three-way valve switching” process in FIGS. 8 to 11), the on-off valve is closed and added. Close the valve piping. This also prevents air and foreign matter introduced into the pipe from the connection from flowing into the addition valve, and efficiently performs residual pressure injection in the addition valve and sucking back urea water on the pump side. Can do.

  Although a mechanical check valve is used in FIG. 1, an intake valve (for example, a shutter valve) that electrically opens and closes the flow path of the branch pipe may be employed instead of the check valve. good. 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. Thus, air can be introduced from the branch pipe into the pipe, and urea water can be sucked back.

  Further, the branch pipe and the check valve are omitted from the configuration of FIG. 1, or the branch pipe, the check valve and the three-way valve are omitted from the configuration of FIG. 6, and the residual pressure injection control is not performed without sucking back the urea water. May only be executed. Also by this, the residual urea water in the addition valve can be reduced, so that the addition valve can be prevented from being damaged due to freezing of the urea water.

  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 during engine operation, the urea water tank side flow path is connected to the pump suction port, and the addition valve side flow path is connected to the pump discharge port. In addition, the flow path switching valve is controlled. 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.

  Moreover, in the said embodiment, although the pressure in the addition valve side piping which the pressure sensor detected was made into the residual pressure in an addition valve, a pressure sensor was connected to an addition valve, and the pressure in an addition valve (residual pressure) May be directly detected.

  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 executes the processes of S2 of FIG. 4, S5 to S9 of FIG. 5, S13 of FIG. 8, S18 of FIG. 9, S22 to S26 of FIG. 10, and S31 to S35 of FIG. It corresponds to “addition control means” in the invention. Further, the three-way valve 9 and the DCU 19 that executes the processing of S12 of FIG. 8, S16 of FIG. 9, S21 of FIG. 10, and S29 of FIG. 11 correspond to the “channel closing means” in the present invention. Further, the DCU 19 that executes the processes of S14 in FIG. 8, S17 and S19 in FIG. 9, S27 in FIG. 10, S30 and S36 in FIG. 11 corresponds to the “pump control means” in the present invention. Further, the branch pipe 10 and the check valve 13 in FIG. 1 correspond to “introducing means” in the present invention. Further, the three-way valve 9, the branch pipe 10, and the check valve 13 in FIG. 6 correspond to the “introducing 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 19 DCU

Claims (13)

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 of the internal combustion engine;
A pipe (8) that forms a flow path for the liquid between the tank and the addition valve;
A pump (7) for supplying the liquid stored in the tank to the addition valve through the pipe when the internal combustion engine is operated;
After the internal combustion engine is stopped, the addition control means (S2, S5 to S5, S5) which opens the addition valve without adding or sucking back the liquid to the addition valve and adds the liquid remaining in the addition valve. S9, S13, S18, S22 to S26, S31 to S35),
An exhaust emission control device (1, 1a) for an internal combustion engine, comprising: Introduction means (10, 13) for introducing air into the pipe from any position of the pipe from the pump to the addition valve when sucking the liquid back into the tank;
After the internal combustion engine is stopped, before or after the addition of the liquid by the addition control means, the pump is controlled so that the liquid remaining on the pump side from the air introduction position by the introduction means is sucked back into the tank. The exhaust emission control device (1) for an internal combustion engine according to claim 1, further comprising pump control means (S3, S10, S14, S27). A flow path closing means (9, S12, S16, S21, S29) for closing a flow path at any position of the pipe from the pump to the addition valve;
The addition control means (S13, S18, S22 to S26, S31 to S35) opens the addition valve while the flow path of the pipe is closed by the flow path closing means after the internal combustion engine is stopped. The exhaust emission control device (1a) for an internal combustion engine according to claim 1, characterized in that: After the internal combustion engine is stopped, the pump is arranged so that the liquid remaining on the pump side from the closed position of the flow path is sucked back into the tank with the flow path closing means closed by the flow path closing means. Pump control means to control (S14, S17, S19, S27, S30, S36);
And an introduction means (9, 10, 13) for introducing air into the pipe (82) on the pump side from the closed position when the liquid is sucked back by the pump control means. The exhaust emission control device for an internal combustion engine according to claim 3.   The said addition control means (S2, S5-S9, S13, S22-S26) opens the said addition valve in the state which the said pump stopped after the said internal combustion engine stopped. An exhaust emission control device for an internal combustion engine according to any one of the preceding claims.   The exhaust purification of an internal combustion engine according to claim 4, wherein the addition control means (S18, S31 to S35) opens the addition valve during the suction of the liquid by the pump control means. apparatus.   The said addition control means performs addition of the said liquid remaining in the said addition valve by the continuous addition control which opens the said addition valve once by one addition control. An exhaust emission control device for an internal combustion engine according to any one of the preceding claims.   The addition control means adds the liquid remaining in the addition valve by intermittent addition control that alternately repeats opening and closing of the addition valve in one addition control. Item 7. An exhaust emission control device for an internal combustion engine according to any one of Items 1 to 6. Pressure detecting means (14) for detecting the pressure in the addition valve or the pipe,
The addition control means (S5 to S9, S22 to S26, S30 to S35) adds the liquid remaining in the addition valve until the pressure detected by the pressure detection means becomes less than a predetermined value. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 8.   The exhaust purification device for an internal combustion engine according to claim 9, wherein the addition control means sets a valve opening condition of the addition valve based on the pressure.   The exhaust purification device of an internal combustion engine according to claim 10, wherein the addition control means lengthens the valve opening time of the addition valve as the pressure increases.   The exhaust purification device for an internal combustion engine according to claim 10 or 11, wherein the addition control means increases the number of times the addition valve is opened as the pressure increases.   13. The liquid according to claim 1, wherein the liquid is urea water for reducing NOx in the exhaust gas in a NOx selective reduction catalyst (4) provided in the exhaust passage. An exhaust purification device for an internal combustion engine.

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