JP4730278B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust gas purification device, and more particularly, to an exhaust gas purification device suitably employed in a urea SCR (Selective Catalytic Reduction) system.

  In recent years, the urea SCR system has been developed as an exhaust purification device for purifying NOx (nitrogen oxide) in exhaust gas with a high purification rate in engines (particularly diesel engines) applied to automobiles and the like. It has been put to practical use. The following configuration is known as a urea SCR system.

  That is, in the urea SCR system, an SCR catalyst is provided in an exhaust pipe connected to the engine body, and a urea water addition valve for adding urea water (urea aqueous solution) as a reducing agent into the exhaust pipe is provided upstream of the SCR catalyst. It has been. A urea water tank is connected to the urea water addition valve via a urea water supply pipe. For example, when the pump disposed in the urea water tank is driven to discharge, the urea water is removed from the urea water tank. The urea water supply valve is supplied through a urea water supply pipe.

  In such a system, the added water is added into the exhaust pipe by the urea water addition valve, whereby the urea water is supplied to the SCR catalyst together with the exhaust gas, and the exhaust gas is purified by the NOx reduction reaction on the SCR catalyst. When NOx is reduced, urea water is hydrolyzed with exhaust heat to generate ammonia (NH3), and ammonia is added to NOx in the exhaust gas selectively adsorbed by the SCR catalyst. Then, NOx is reduced and purified by performing a reduction reaction based on ammonia on the SCR catalyst.

By the way, in the above-described urea SCR system, urea water used as a reducing agent is frozen at, for example, −11 ° C., and the use of urea water is hindered along with the freezing. Therefore, as a countermeasure against freezing of urea water, a cooling water circulation pipe that leads part of the engine cooling water to the urea water tank is provided, and a cooling water shut-off valve is provided in the middle of the cooling water circulation pipe. A technique has been proposed in which the cooling water is circulated through the cooling water circulation pipe (see, for example, Patent Document 1).
JP 2006-125331 A

  In the case of the prior art such as Patent Document 1 described above, urea water can be used (NOx reduction or purification by adding urea water) by thawing the urea water after the engine is started. This is a measure that can be effective after freezing, and no measures are taken to prevent freezing. For this reason, it is considered that inconvenience caused by freezing cannot be solved. In other words, if it is noticed that the volume increases by about 7% when the urea water freezes, it is considered that the urea water supply pipe or the like may be damaged due to the increase in volume.

  The main object of the present invention is to provide an engine exhaust gas purification apparatus that can prevent freezing of a reducing agent such as urea water and thereby suppress damage to components of the reducing agent supply system. .

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

In the engine exhaust gas purification apparatus according to the present invention, the reducing agent (urea aqueous solution or the like) in the reducing agent container is pumped to the reducing agent passage by driving the pump during engine operation, and the reducing agent is fed into the exhaust passage by the reducing agent addition valve. To be added. Thereby, a specific exhaust purification reaction based on the addition of the reducing agent is promoted in the exhaust purification catalyst (reduction catalyst). Then, in such an exhaust purifying apparatus, in this onset bright particular, after stopping the engine, and to be driven in a state suck back different reducing agent and the pump reducing agent pumping state.

  In short, when the engine is operating, the reducing agent passage is filled with the reducing agent, and after the engine is stopped, the reducing agent passage is similarly filled with the reducing agent. In this case, when the reducing agent freezes in the cold district at night or the like, its volume increases, and there is a risk that the piping or the like for constituting the reducing agent passage may be damaged. In this regard, in the present invention, after the engine is stopped, the reducing agent in the reducing agent passage is sucked back to the reducing agent container side by driving the pump in the reducing agent sucking back state different from the reducing agent pumping state. The reducing agent (residual reducing agent) in the agent passage is collected in the reducing agent container. As a result, freezing of the reducing agent remaining in the reducing agent passage or the like is prevented, and as a result, damage to the components of the reducing agent supply system can be suppressed.

  The present invention is considered to be particularly useful in a so-called returnless system in which the reducing agent addition valve or the like is not provided with a return pipe for returning the reducing agent to the reducing agent container.

  As the reducing agent pump, for example, a configuration that can rotate in both forward and reverse directions, pumps the reducing agent by rotating in the forward direction, and sucks the reducing agent by rotating in the opposite direction is applied. Good. Alternatively, as the same pump, a reducing agent pumping pump portion and a reducing agent sucking back pump portion are provided, and by selectively driving each pump portion, the reducing agent pumping state and the reducing agent sucking back state are established. It is also possible to adopt a configuration for switching.

After stopping the engine, the pump has good when driven with suck back a reducing agent as well as the reducing agent addition valve in an open state. In this case, the reducing agent is sucked back (if the reducing agent pumping state is set to the normal rotation state, the reverse rotation state), and the reducing agent addition valve is opened so that the reducing agent is sucked back and the reducing agent added. Air is introduced into the reducing agent passage from the valve (addition port of the reducing agent addition valve), and the reducing agent remaining in the reducing agent passage can be efficiently recovered.

As described above, after the engine is stopped, in the configuration in which the reducing agent addition valve is opened and the pump is in the reducing agent sucking back state, the pump is first driven in the reducing agent sucking back state, and then the reducing agent adding valve is turned on. When it opens state not good. As a result, the reducing agent pressure in the reducing agent passage can be reduced (for example, a negative pressure is generated) before the reducing agent addition valve is opened. The reducing agent can be prevented from leaking into the exhaust passage from the opening).

In addition, a branch passage is provided in the vicinity of the reducing agent addition valve in the reducing agent passage, and an intake valve that opens when the pump is driven in the reducing agent suction state and introduces air from the outside is provided in the branch passage. door not good. In this case, after the engine is stopped, when the pump is driven in the reducing agent sucking back state, air is introduced from the outside into the reducing agent passage through the intake valve, and the reducing agent remaining in the reducing agent passage is efficiently recovered. be able to.

  As an intake valve, a mechanical check valve that is opened by a negative pressure in the reducing agent passage when the pump is driven in the reducing agent sucking back state, or an electric valve when the pump is driven in the reducing agent sucking back state. An open / close solenoid valve or the like can be applied.

As described above, in the configuration in which the branch passage is provided in the vicinity of the reducing agent addition valve in the reducing agent passage and the intake valve is provided in the branch passage, the residual reducing agent in the reducing agent passage is to some extent after the engine is stopped. Although it can be recovered, it is considered that the reducing agent remains between the branch portion of the branch passage and the reducing agent addition valve (including the passage portion inside the reducing agent addition valve). Therefore, the following configuration can be considered as a countermeasure.

  That is, after the engine is stopped, the reducing agent addition valve is closed and the pump is driven in the reducing agent sucking back state (first means), and then the reducing agent addition valve is opened and the pump is pumped with the reducing agent. Drive in the state (second means). In such a case, after the engine is stopped, the reducing agent addition valve is closed and the pump is driven in the reducing agent sucking back state so that air is introduced from the outside into the reducing agent passage through the intake valve. , The remaining reducing agent is recovered at a portion other than between the branching portion of the branching passage and the reducing agent addition valve (including the passage portion inside the reducing agent addition valve). Next, the reducing agent addition valve is opened, and the pump is driven in the reducing agent pumping state, so that the branch portion of the branch passage and the reducing agent addition valve (including the passage portion inside the reducing agent addition valve) The remaining reducing agent is discharged from the reducing agent addition valve into the exhaust passage.

  According to the said structure, it can avoid that a reducing agent remains between the branch part of a branch passage and a reducing agent addition valve (a channel part inside a reducing agent addition valve is included). Therefore, it is possible to suppress damage to the components (reducing agent supply pipe and reducing agent addition valve) of the reducing agent supply system due to freezing of the residual reducing agent. Note that when the reducing agent addition valve is opened by the second means, the reducing agent is slightly discharged into the exhaust passage, but since the discharge amount is limited, the inconvenience in reducing agent consumption is considered to be minor. It is done.

  According to the first means and the second means described above, almost all of the residual reducing agent in the reducing agent passage is discharged, but the pump is driven from the reducing agent container by the second means (driving in the reducing agent pumping state). It is considered that the reducing agent is newly sucked into the reducing agent passage. Therefore, following the processing by the second means, it is preferable to close the reducing agent addition valve and drive the pump in the reducing agent sucking back state (third means). Thereby, after discharge of the residual reducing agent, the reducing agent newly sucked into the reducing agent passage can also be collected in the reducing agent container.

Further, as a reducing agent addition valve, a first passage for guiding the reducing agent supplied through the reducing agent passage to the addition port, and a second passage formed by branching from the first passage in the vicinity of the addition port are provided. The provided configuration is adopted. Then, on the second path or paths leading to that of the reducing agent addition valve, the pump is not good when opened by providing an intake valve for introducing air from the outside when it is driven in a state suck back the reducing agent. As an intake valve, a mechanical check valve that is opened by a negative pressure in the reducing agent passage when the pump is driven in the reducing agent sucking back state, or an electric valve when the pump is driven in the reducing agent sucking back state. An open / close solenoid valve or the like can be applied.

  According to the above configuration, when the pump is driven in the reductant sucking back state after the engine is stopped, the first passage of the reducing agent addition valve (the first passage near the addition port) and the second passage through the intake valve and the second passage; Air is introduced into the reducing agent passage from the outside, and the reducing agent remaining in the first passage and the reducing agent passage of the reducing agent addition valve can be efficiently recovered. In this case, almost all of the residual reducing agent in the reducing agent supply system can be recovered by one pump drive (suction back drive).

In the configuration in which the second passage is provided in the reducing agent addition valve and the intake valve is provided on the second passage or a path leading to the second passage, there is a concern that the reducing agent may leak to the outside due to oil tightness failure in the intake valve. Therefore, not good when installing the intake valve in the space portion of the reducing agent in the container. In this case, even if the reducing agent leaks to the outside due to poor oil tightness in the intake valve, the leaked reducing agent can be recovered as it is in the reducing agent container.

Further, in the configuration in which the second passage is provided in the reducing agent addition valve as described above, the pressure for adjusting the pressure of the reducing agent in the reducing agent passage on the path leading to the second passage of the reducing agent addition valve. an adjusting device is provided, the reducing agent becomes excessive upon pressure adjustment by the pressure adjusting device has good when configured to discharge the reducing agent in the container. According to this configuration, when the reducing agent is used during operation of the engine (addition supply to the exhaust passage), a part of the reducing agent supplied to the reducing agent addition valve flows from the second passage to the pressure adjusting device and is reduced. The surplus of the agent is sequentially discharged into the reducing agent container. Therefore, the flow of the reducing agent from the reducing agent addition valve to the reducing agent container (circulation of the reducing agent) occurs, and the reducing agent addition valve can be cooled by the reducing agent. In addition, it is also possible here to install a pressure regulator in a reducing agent container.

In the present exhaust purification apparatus, the reducing agent is a urea aqueous solution, and the exhaust purification catalyst uses the NOx reduction reaction for reducing NOx by ammonia generated from the urea aqueous solution as the exhaust purification reaction, and promotes the NOx reduction reaction. it is intended to and not good.

  As represented by the urea SCR system, a NOx purification device using an aqueous urea solution as a reducing agent is expected as an exhaust purification device that purifies NOx in exhaust gas at a high purification rate. Thus, the present invention is particularly beneficial when applied to a urea SCR system. In addition, for example, when this exhaust purification device is adopted in the field of automobiles and this device is mounted on a vehicle equipped with a diesel engine, the generation of NOx is allowed in the combustion process to improve fuel consumption and PM. As a result, it becomes possible to greatly contribute to improving the performance of automobiles and purifying exhaust gas.

[First Embodiment]
Hereinafter, a first embodiment of an exhaust emission control device according to the present invention will be described with reference to the drawings. The exhaust purification device of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as a urea SCR system. First, the configuration of this system will be described in detail with reference to FIG. FIG. 1 is a configuration diagram showing an outline of a urea SCR system according to the present embodiment.

  As shown in FIG. 1, the present system uses exhaust discharged from a diesel engine (not shown) mounted on an automobile as a purification target, and generally includes various actuators and various sensors for purifying exhaust, and an ECU ( (Electronic control unit) 30 and the like.

  Specifically, an exhaust pipe 11 connected to an engine body (not shown) is provided as a configuration of the engine exhaust system. The exhaust pipe 11 includes a DPF (Diesel Particulate Filter) 12 and a selective reduction catalyst (hereinafter referred to as an SCR catalyst). 13) is provided. Further, a urea water addition valve 15 for adding and supplying urea water (urea aqueous solution) as a reducing agent into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11.

  In the exhaust pipe 11, an exhaust sensor 16 having both a NOx detection unit (NOx sensor) and an exhaust temperature detection unit (exhaust temperature sensor) is provided on the downstream side of the SCR catalyst 13. On the downstream side, the amount of NOx in the exhaust (and thus the NOx purification rate by the SCR catalyst 13) and the temperature of the exhaust are detected. Further downstream of the exhaust pipe 11, an ammonia removal device (for example, an oxidation catalyst) for removing excess ammonia (NH3), an ammonia sensor for detecting the amount of ammonia in the exhaust, and the like are provided as necessary. .

  The DPF 12 is a continuous regeneration PM removal filter that collects PM (particulate matter) in exhaust gas. The DPF 12 carries a platinum-based oxidation catalyst and can remove HC and CO together with a soluble organic component (SOF) which is one of the PM components. Incidentally, the PM collected by the DPF 12 can be removed by combustion by post-injection after the main fuel injection in the diesel engine or the like (corresponding to the regeneration process), whereby the DPF 12 can be used continuously.

The SCR catalyst 13 promotes a NOx reduction reaction (exhaust gas purification reaction).
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 12H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)
Such a reaction is promoted to reduce NOx in the exhaust gas. A urea water addition valve 15 provided on the upstream side of the SCR catalyst 13 is additionally supplied with ammonia (NH 3) as a NOx reducing agent in these reactions.

  The urea water addition valve 15 has substantially the same configuration as an existing fuel injection valve (injector), and since a known configuration can be adopted, the configuration will be briefly described here. The urea water addition valve 15 is configured as an electromagnetic on-off valve including a drive unit including an electromagnetic solenoid and a valve body unit having a needle for opening and closing the tip addition port. Open or close based on this. 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, the tip addition port is opened by the needle movement, and urea water is added (injected).

  The urea water is sequentially supplied from the urea water tank 21 to the urea water addition valve 15. Next, the configuration of the urea water supply system will be described.

  The urea water tank 21 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined concentration is stored therein. As a countermeasure against freezing of urea water in the tank, it is possible to attach a heater to the urea water tank 21 or arrange a heat insulating material such as a heat insulating sheet around the tank.

  A urea water pump 22 is provided in the urea water tank 21 while being immersed in the urea water. The urea water pump 22 is an electric pump (for example, a three-phase AC motor) that is rotationally driven by a drive signal from the ECU 30, and can rotate in either the forward or reverse direction. One end of a urea water supply pipe 23 is connected to the urea water pump 22, and the other end of the urea water supply pipe 23 is connected to the urea water addition valve 15. A urea water passage is formed in the urea water supply pipe 23 and corresponds to a “reducing agent passage”. When the urea water pump 22 is rotationally driven in the normal rotation direction, urea water is pumped up and discharged to the urea water addition valve 15 side through the urea water supply pipe 23.

  The urea water supply pipe 23 is provided with a filter 24 for filtering the urea water and a pressure adjustment valve 25 for adjusting the pressure of the urea water. Accordingly, foreign water is removed from the urea water discharged from the urea water pump 22 by the filter 24, and then the pressure is adjusted to a predetermined supply pressure by the pressure adjustment valve 25. The excess urea water as a result of the pressure adjustment is returned to the urea water tank 21 through the return pipe 26. The urea water supply pipe 23 is provided with a pressure sensor 27 for detecting the pressure of the urea water in the urea water supply pipe 23 and a temperature sensor 28 for detecting the temperature of the urea water. .

  Next, the configuration of the urea water pump 22 will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the internal structure of the urea water pump 22, which conforms to a pump structure that is also used as a vehicle fuel pump. Here, a configuration using a brushless motor as the urea water pump 22 will be described.

  The urea water pump 22 is configured by incorporating a pump part 42 and a brushless motor part 43 in a cylindrical housing 41. The structure of the pump portion 42 will be described. A pump casing 44 and a pump cover 45 are fixed to one end portion of the housing 41 by press fitting, caulking or the like, and a pump chamber 46 is interposed between the pump casing 44 and the pump cover 45. Is formed. In the pump chamber 46, an impeller 47 that is fitted to the rotating shaft 56 of the motor unit 43 is accommodated.

  On the other hand, the motor unit 43 is composed of, for example, a three-phase full-wave drive type brushless motor, and is configured as follows. A cylindrical stator 51 is fitted and fixed in the housing 41, and a plurality of salient poles 52 are formed on the stator 51. These salient poles 52 are provided with a three-phase armature coil 53. A magnet rotor 55 is disposed on the inner peripheral side of the stator 51. The magnet rotor 55 includes a rotor core 57 fitted to the rotary shaft 56 and, for example, eight field magnets 58 fixed to the outer periphery of the rotor core 57 by adhesion or the like. The eight magnets 58 are arranged so that N poles and S poles are alternately arranged, and thereby an eight pole magnet rotor 55 is configured. Both ends of the rotating shaft 56 of the magnet rotor 55 are rotatably supported by bearings 61 and 62.

  In addition, a drive control circuit 63 of a three-phase full wave drive system is assembled in the housing 41, and when the motor is driven, the drive control circuit 63 sequentially switches the energization of the armature coils 53 of each phase by the three-phase energization system. It is done. A housing cover 66 having a discharge port 65 is fitted into the opening of the housing 41 on the drive control circuit 63 side. The drive control circuit 63 may be provided outside the pump without being integrated with the pump.

  When the impeller 47 of the pump unit 42 is rotationally driven by the motor unit 43, the urea water in the urea water tank 21 is sucked into the pump chamber 46 from the suction port (not shown) of the pump cover 45, and the pump casing 44 It is discharged from the discharge port to the urea water chamber (urea water passage) in the housing 41. The urea water flows through a gap (urea water passage) between the stator 51 and the magnet rotor 55, is discharged from the discharge port 65 of the housing cover 66 to the urea water supply pipe 23, and is sent to the urea water addition valve 15. It is done.

  Here, the urea water pump 22 has a configuration in which the motor rotation direction is reversed reversely by changing the excitation order of the three-phase armature coil 53, and the urea water is fed to the urea water supply pipe 23 side. In addition to discharging, the urea water can be sucked from the urea water supply pipe 23. That is, when the urea water pump 22 is driven to rotate forward, urea water is discharged from the urea water tank 21, and when the urea water pump 22 is driven to rotate backward, the urea water is sucked back into the urea water tank 21. It is supposed to be.

  The ECU 30 is a part of the system that mainly performs control relating to exhaust gas purification as an electronic control unit. The ECU 30 includes a well-known microcomputer (not shown), and operates various actuators including the urea water addition valve 15 in a desired mode based on detection values of various sensors, thereby performing various types of exhaust purification. The control is performed. Specifically, for example, by controlling the energization time of the urea water addition valve 15 and the driving amount of the urea water pump 22, an appropriate amount of urea water is added and supplied into the exhaust pipe 11 at an appropriate time.

In the system according to the present embodiment, during the engine operation, the urea water in the urea water tank 21 is pumped to the urea water addition valve 15 through the urea water supply pipe 23 by driving the urea water pump 22, and the urea water addition valve 15. Thus, urea water is added and supplied into the exhaust pipe 11. Then, urea water is supplied to the SCR catalyst 13 together with the exhaust gas in the exhaust pipe 11, and the exhaust gas is purified by the NOx reduction reaction in the SCR catalyst 13. When reducing NOx, for example,
(NH2) 2CO + H2O → 2NH3 + CO2 (Formula 4)
As a result of the above reaction, urea water is hydrolyzed with exhaust heat to produce ammonia (NH3), and this ammonia is added to NOx in the exhaust selectively adsorbed by the SCR catalyst 13. . Then, the reduction reaction based on the ammonia (the above reaction formulas (Formula 1) to (Formula 3)) is performed on the SCR catalyst 13, whereby NOx is reduced and purified.

  By the way, urea water used as a reducing agent freezes at −11 ° C., and the volume increases by about 7% with the freezing. In this case, when urea water remains in each component (urea water addition valve 15 and urea water supply pipe 23) of the urea water supply system after the engine is stopped, and the volume of the residual urea water increases due to freezing, The water addition valve 15 and the urea water supply pipe 23 may be damaged. Therefore, in this embodiment, as a countermeasure against urea water freezing, after the engine is stopped, the urea water pump 22 is driven in a urea water sucking back state (reverse rotation driving state) different from the normal urea water pressure feeding state (forward rotation driving state). The urea water remaining in the urea water addition valve 15 and the urea water supply pipe 23 is collected in the urea water tank 21.

  FIG. 3 is an explanatory diagram showing a state in which the urea water addition valve 15 and the urea water remaining in the urea water supply pipe 23 are collected in the urea water tank 21 by the reverse rotation driving of the urea water pump 22 after the engine is stopped. .

  In FIG. 3, after the engine is stopped, the urea water pump 22 is reversely driven, and the urea water addition valve 15 is energized to open the tip addition port of the urea water addition valve 15. At this time, for the purpose of avoiding leakage of urea water into the exhaust pipe 11, it is preferable that the urea water pump 22 is driven first in the reverse rotation state, and then the urea water addition valve 15 is energized. However, the reverse rotation drive of the urea water pump 22 and the energization of the urea water addition valve 15 can be performed simultaneously.

  As described above, the urea water pump 22 is reversely driven, and the urea water addition valve 15 is opened, so that the residual urea water in the urea water addition valve 15 and the urea water supply pipe 23 is removed from the urea water tank 21. Sucked back to the side and collected in the tank 21. This eliminates the inconvenience that the urea water addition valve 15 and the urea water supply pipe 23 are damaged due to the increase in volume accompanying freezing of the urea water. At this time, the urea water suction time (reverse rotation drive time of the urea water pump 22) is determined by the volumes of the urea water addition valve 15 and the urea water supply pipe 23 and the pump suction capacity.

  FIG. 4 is a flowchart showing a processing procedure for urea water suck-back control. This process is repeatedly executed by the ECU 30 at a predetermined time period, for example.

  In FIG. 4, in step S11, it is determined whether or not the engine is stopped, and in step S12, it is determined whether or not the urea water suction has been completed. The determination after the engine is stopped is performed, for example, by determining that the engine speed is 0 or that the ignition switch is OFF. The suck back completion determination is performed by determining whether or not the suck back completion flag is 1 (suck back complete = 1). Then, the process proceeds to step S13 on the condition that after the engine is stopped and the urea water suction is not completed.

  In step S13, it is determined whether or not a predetermined time has elapsed after the urea water sucking back (reverse rotation driving of the urea water pump 22) is started. If the predetermined time has not elapsed, steps S14 and S15 are executed. That is, in step S14, the urea water pump 22 is driven to rotate backward (that is, driven in the urea water sucking back state), and in step S15, the urea water addition valve 15 is energized. At this time, it is preferable to start energization of the urea water addition valve 15 with a delay of about several seconds from the start of the reverse rotation driving of the urea water pump 22.

  Further, when a predetermined time has elapsed after the urea water sucking back is started, steps S16 and S17 are executed. That is, in step S16, the driving of the urea water pump 22 is stopped, and in step S17, the energization of the urea water addition valve 15 is ended. Thereafter, in step S18, 1 is set to the suck back completion flag.

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

  In the urea SCR system, after the engine is stopped, the urea water addition valve 15 is opened and the urea water pump 22 is driven to rotate in reverse, so that the residual urea water in the urea water addition valve 15 and the urea water supply pipe 23 is driven. Can be recovered in the urea water tank 21. As a result, the urea water is prevented from freezing in the urea water addition valve 15 and the urea water supply pipe 23, and as a result, damage to these members can be suppressed. That is, it is possible to protect each component of the urea water supply system.

  Since the urea water addition valve 15 is opened at the time of sucking back the urea water, air is introduced from the tip addition port of the urea water addition valve 15 to the urea water supply pipe 23, and residual urea in the urea water supply pipe 23. Water can be recovered efficiently.

  If the urea water can be prevented from freezing in the urea water addition valve 15 and the urea water supply pipe 23, the urea water can be used early at the next engine start. Therefore, the exhaust purification effect is improved and exhaust emission can be improved.

  This embodiment can be suitably realized in a so-called returnless type urea SCR system that does not include a return path for returning the urea water surplus at the urea water addition valve 15 to the urea water tank 21 side. That is, in a return type urea SCR system having a return path, it is considered that urea water in the urea water supply pipe 23 is discharged through the return path. In a returnless type system, urea in the urea water supply pipe 23 is considered. It becomes difficult to discharge water. In this regard, according to the present embodiment, the urea water in the urea water supply pipe 23 can be easily and reliably discharged even in a returnless type system.

  When the urea water pump is sucked back, the urea water pump 22 is first driven in the reverse rotation state (urea water sucking back state), and then the urea water addition valve 15 is opened, so that the urea water addition valve 15 is opened. Before the valve, the urea water pressure in the urea water supply pipe 23 can be reduced (for example, a negative pressure is generated). Therefore, the urea water can be prevented from leaking into the exhaust pipe 11 from the tip addition port when the urea water addition valve 15 is opened.

  By using a three-phase AC motor as the urea water pump 22, it is possible to easily realize a configuration capable of rotating in both forward and reverse directions, that is, a configuration capable of both feeding and sucking urea water. In this case, the state switching between urea water pressure feeding / urea water sucking back can be performed only by switching the pump rotation direction, which is considered to be highly practical.

  Since the injector type electromagnetic on-off valve is used as the urea water addition valve 15, ON / OFF of urea water addition, control of the urea water addition amount, and the like can be performed arbitrarily and with high accuracy. Thereby, useless consumption of urea water can be suppressed and urea water consumption can be reduced.

  The urea water addition valve 15 is provided downstream of the DPF 11 (PM removal filter). As a result, the disadvantage that the tip addition port of the urea water addition valve 15 is contaminated by PM can be suppressed, and the urea water addition valve 15 can be used over a long period of time.

  Urea water is used as a reducing agent for the SCR catalyst 13, and the SCR catalyst 13 promotes a NOx reduction reaction (the above reaction formulas (Formula 1) to (Formula 3)) in which NOx is reduced by ammonia generated from the urea water. The system was installed in a vehicle equipped with a diesel engine. As a result, it is possible to improve the fuel consumption and PM by allowing the generation of NOx in the combustion process, and as a result, it can greatly contribute to the improvement of the performance of the automobile and the cleaner exhaust.

[Second Embodiment]
Next, the urea SCR system in the second embodiment will be described focusing on the differences from the first embodiment. FIG. 5 is a configuration diagram of a system in the present embodiment. In FIG. 5, the same components as those in the system configuration of FIG. 1 described above are denoted by the same member numbers and the description thereof is omitted.

  As shown in FIG. 5, a branch pipe 71 is provided near the urea water addition valve 15 in the urea water supply pipe 23, and an intake valve 72 is provided in the branch pipe 71. The intake valve 72 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. In this system, the urea water pump 22 rotates in reverse (after urea water absorption) after the engine is stopped. When driven in the return state), it is opened by the negative pressure in the urea water supply pipe 23 and air is introduced from the outside. It is also possible to use an electromagnetic on-off valve as the intake valve 72 and to be electrically opened when the urea water pump 22 is driven in reverse rotation (urea water sucking back state) after the engine is stopped. is there.

  Here, as urea water suck-back control after the engine is stopped, the following processes (1) to (3) are performed in order.

  (1) As the first process, the urea water addition valve 15 is not energized and remains in the closed state, and the urea water pump 22 is driven in the reverse rotation (urea water sucking back state) (corresponding to “first means”). .

  (2) Next, as the second process, the urea water addition valve 15 is energized to open, and the urea water pump 22 is driven in the normal rotation (urea water pressure feeding state) (corresponding to “second means”). .

  (3) Next, as a third process, the urea water addition valve 15 is de-energized again to close it, and the urea water pump 22 is again driven in the reverse rotation (urea water sucking back state) ("third means"). Equivalent).

  FIG. 6 is a flowchart showing a processing procedure of urea water suck-back control in the present embodiment. This process is repeatedly executed by the ECU 30 in place of the process shown in FIG.

  In FIG. 6, in step S21, it is determined whether or not the engine has been stopped. In step S22, it is determined whether or not the urea water suck-back has been completed (same as steps S11 and S12 in FIG. 4). . Then, the process proceeds to step S23 on condition that the urea water sucking back is not completed after the engine is stopped.

  In step S23, it is determined whether or not the first process is completed. If the first process is not completed, the process proceeds to step S24 to execute the first process. That is, the urea water addition valve 15 is closed and the urea water pump 22 is driven in the reverse rotation (urea water sucking back state).

  If the first process has ended, it is determined in step S25 whether the second process has ended. And if it is before completion | finish of a 2nd process, it will progress to step S26 and will perform a 2nd process. That is, the urea water addition valve 15 is opened, and the urea water pump 22 is driven in the forward rotation (urea water pressure feeding state).

  If the second process has ended, it is determined in step S27 whether the third process has ended. And if it is before completion | finish of a 3rd process, it will progress to step S28 and will perform a 3rd process. That is, the urea water addition valve 15 is closed again and the urea water pump 22 is driven in the reverse rotation (urea water sucking back state). If the third process has been completed, the process proceeds to step S29, and 1 is set to the suck back completion flag.

  Next, how the residual urea water in the urea water addition valve 15 and the urea water supply pipe 23 is collected in the urea water tank 21 after the engine is stopped will be described with reference to FIG. 7A shows the execution state of the first process, FIG. 7B shows the execution state of the second process, and FIG. 7C shows the execution state of the third process.

  In FIG. 7A, after the engine is stopped, the urea water addition valve 15 is closed (energization OFF), and the urea water pump 22 is driven in reverse rotation (first process). As a result, the residual urea water is sucked back and collected in the urea water tank 21 while the external air is introduced into the urea water supply pipe 23 through the intake valve 72 and the branch pipe 71. At this time, the urea water suction time (reverse rotation drive time of the urea water pump 22) is the volume of the portion of the urea water supply pipe 23 excluding the portion between the branch point of the branch pipe 71 and the urea water addition valve 15. Or it is determined by the pump suction capacity.

  According to (a) above, the recovery of the residual urea water is completed for the portion of the urea water supply pipe 23 excluding the portion between the branch point of the branch pipe 71 and the urea water addition valve 15. However, urea water remains in the urea water supply pipe 23 from the branch point of the branch pipe 71 to the urea water addition valve 15 and in the urea water addition valve 15 (A1 portion in the figure).

  Therefore, next, as shown in FIG. 7B, the urea water addition valve 15 is opened (energization ON), and the urea water pump 22 is driven in the forward rotation (second process). Thereby, the urea water remaining in the urea water supply valve 23 from the branch point of the branch pipe 71 to the urea water addition valve 15 and in the urea water addition valve 15 is discharged from the urea water addition valve 15 into the exhaust pipe 11. Is done. At this time, since the residual urea water is relatively small at the time of the second treatment, the normal rotation driving time of the urea water pump 22 is relatively short.

  According to (b) above, most of the residual urea water is discharged from the urea water addition valve 15 and the urea water supply pipe 23. However, the urea water in the urea water tank 21 is newly sucked up as the urea water pump 22 is driven to rotate forward (A2 portion in the figure). In addition, according to this process, urea water is discharged into the exhaust pipe 11 to some extent, but since the discharge amount is limited, it is considered that the inconvenience in consumption of urea water is slight.

  Therefore, next, as shown in FIG. 7C, the urea water addition valve 15 is again closed (energization OFF) and the urea water pump 22 is driven in reverse rotation (third process). As a result, the urea water newly sucked in the urea water supply pipe 23 is also collected in the urea water tank 21.

  By the above series of control operations, the remaining urea water in the urea water addition valve 15 and the urea water supply pipe 23 is completely made into the urea water tank 21. This eliminates the inconvenience that the urea water addition valve 15 and the urea water supply pipe 23 are damaged due to the increase in volume accompanying freezing of the urea water.

  According to the second embodiment described in detail above, the urea solution remaining in the urea solution addition valve 15 and the urea solution supply pipe 23 is recovered in the urea solution tank 21 after the engine is stopped, as in the first embodiment. It is possible to suppress breakage of each member accompanying freezing of urea water.

  Further, in the first embodiment, when recovering (sucking back) the residual urea water, the urea water addition valve 15 is opened and air in the exhaust pipe 11 is introduced from the tip addition port, so that it exists in the exhaust pipe 11. There is a risk of sucking foreign matter (including foreign matter in exhaust) into the urea water supply pipe 23. In this regard, in the second embodiment, there is no possibility that foreign matter in the exhaust pipe 11 is sucked from the tip addition port of the urea water addition valve 15. This eliminates the possibility of malfunction in the urea water addition valve 15 due to the mixing of foreign matter or the like. Moreover, the contamination in the urea water supply pipe 23 can also be suppressed.

[Third Embodiment]
Next, the urea SCR system in the third embodiment will be described focusing on the differences from the first embodiment. In the present embodiment, a urea water addition valve 80 having a configuration different from the urea water addition valve 15 described above is used as the reducing agent addition valve, and FIG. 8 shows a cross-sectional configuration of the urea water addition valve 80. In the present embodiment, the same components as those in the system configuration of FIG. 1 described above are denoted by the same member numbers and the description thereof is omitted.

  A cross-sectional configuration of the urea water addition valve 80 will be described with reference to FIG. The urea water addition valve 80 is an electromagnetic on-off valve that includes a drive unit 81 and a valve body unit 82. The drive unit 81 includes an electromagnetic solenoid 83 and is energized by an energization signal input from the terminal 84. The main part of the valve body 82 is a needle 87 housed in the casing 86, a nozzle body 88 assembled to the casing 86 and slidably holding the tip of the needle 87, and the needle 87 closed. A coil spring 89 that biases in the direction, and an outer peripheral cover 90 provided on the outer peripheral side of the casing 86 and the nozzle body 88 are provided.

  In the casing 86 and the nozzle body 88, urea water passages 86a and 88a for allowing the urea water taken from the urea water suction port 92 to flow are provided. A tip addition port 88 b is formed at the tip of the nozzle body 88. Further, an outer passage 93 is provided between the casing 86 and the nozzle body 88 and the outer peripheral cover 90, and the urea water passages 86 a and 88 a and the outer passage 93 are connected by a communication passage 88 c formed in the nozzle body 88. It is communicated. The urea water passages 86a and 88a correspond to “first passages” for guiding the urea water supplied through the urea water supply pipe 23 to the tip addition port 88b, and the outer passage 93 is urea near the tip addition port 88b. This corresponds to a “second passage” formed by branching from the water passages 86a and 88a.

  In the casing 86, an intake valve 95 is provided at a port portion 94 that communicates with the outer passage 93. The intake valve 95 is constituted by 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 in the outer passage 93. In this system, the urea water pump 22 is reversed after the engine is stopped. When driven by rotation (urea water sucking back state), the air is released by the negative pressure in the outer passage 93 and air is introduced from the outside. It is also possible to use an electromagnetic on-off valve as the intake valve 95 and to be electrically opened when the urea water pump 22 is driven in reverse rotation (urea water sucking back state) after the engine is stopped. is there.

  In the urea water addition valve 80 configured as described above, when the electromagnetic solenoid 83 is energized by the energization signal from the ECU 30, the needle 87 moves in the valve opening direction along with the energization, and the tip 87 is opened by the movement of the needle 87. Then, urea water is added (injected). In normal times, the intake valve 95 is kept closed.

  Incidentally, the urea water addition valve 80 has the above-described urea water in that it has an outer cover 90, an outer passage 93 is formed by the outer cover 90, and an intake valve 95 is provided in the port portion 94. Although it differs from the addition valve 15 (1st Embodiment etc.), it becomes the common structure except those differences.

  FIG. 9 is a schematic diagram showing a state in which residual urea water in the urea water addition valve 80 and the urea water supply pipe 23 is collected in the urea water tank 21 after the engine is stopped.

  In FIG. 9, after the engine is stopped, the urea water pump 22 is reversely driven while the urea water addition valve 80 is in a closed state (energization OFF). Thereby, air is introduced from the outside into the urea water addition valve 80 through the intake valve 95, and the external air flows in the urea water addition valve 80 through the outer passage 93, the communication passage 88c, the urea water passages 86a, 88a, and the like ( Urea water flows backward). At this time, the residual urea water is sucked back on the external air flow (air flow) and collected in the urea water tank 21. At this time, the urea water suction time (reverse rotation drive time of the urea water pump 22) is the urea water addition valve 80 (volume including the urea water passages 86a and 88a, the communication passage 88c, the outer passage 93, etc.) and urea. It is determined by the volume of the water supply pipe 23 and the pump suction capacity.

  As described above, according to the third embodiment, the urea solution remaining in the urea solution addition valve 80 and the urea solution supply pipe 23 can be collected in the urea solution tank 21 after the engine is stopped, as in the first embodiment. It is possible to suppress breakage of each member accompanying freezing of urea water.

  Further, the urea water addition valve 80 is provided with an outer passage 93 (second passage) formed by branching from the urea water passages 86a and 88a in the vicinity of the tip addition port 88b, and a port portion 94 communicating with the outer passage 93. Since the intake valve 95 is provided to the urea water remaining in the urea water addition valve 80 when the urea water is sucked back after the engine is stopped. In this case, almost all of the residual urea water in the urea water supply system including the urea water addition valve 80 and the urea water supply pipe 23 can be recovered by one pump drive (suck back drive).

[Another embodiment]
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the above embodiment, it has been described that urea water is sucked back by driving the urea water pump 22 on the condition that the engine is stopped (see the flowcharts of FIGS. 4 and 6). The execution conditions for the urea water suck back may be defined. For example, there is provided a means for measuring the outside air temperature when the engine is stopped and the urea water is sucked back on condition that the outside air temperature is a predetermined low temperature value (that is, the urea water may be frozen). It is also good. Alternatively, a means for measuring the outside air temperature during a time zone when the outside air temperature falls at night or the like is provided, and the urea water is supplied on condition that the engine is stopped and the outside air temperature measured during the time zone is a predetermined low temperature value. It is good also as a structure which performs sucking back.

In the second embodiment, three processes (first process to third process) are sequentially performed as the suck back control process, but this is changed. For example, only the first process and the second process may be performed. In this case, as the suck back control process,
(1) The urea water addition valve 15 is deenergized and left in the closed state, and the urea water pump 22 is driven in the reverse rotation (urea water sucking back state).
(2) Energize the urea water addition valve 15 to open the urea water pump 22 and drive the urea water pump 22 in the normal rotation (urea water pressure feeding state).
Are performed in the order of (1) → (2).

  Also in this configuration, the remaining urea water in the urea water addition valve 15 and the urea water supply pipe 23 can be almost recovered, and the urea water addition valve 15 and the urea water supply pipe 23 can be prevented from being damaged.

  In the third embodiment, in the urea water addition valve 80, the intake valve 95 is provided in the port portion 94 that communicates with the outer passage 93 serving as the second passage. There is concern about water leaking outside. Therefore, an intake valve is installed in a space in the urea water tank 21. FIG. 10 shows a schematic configuration thereof. In FIG. 10, a urea water pipe 101 is connected to the port portion 94 (see FIG. 8) of the urea water addition valve 80, and the urea water pipe 101 extends to the urea water tank 21 and the urea water tank 21. An intake valve 102 is provided in the space inside. The intake valve 102 has a configuration similar to that of the intake valve 95, and is configured by 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 in the urea water pipe 101 ( However, an electromagnetic on-off valve is also possible.)

  In the configuration shown in FIG. 10, even if a situation occurs in which urea water leaks to the outside due to poor oil tightness in the intake valve 102, the leaked urea water can be recovered as it is in the urea water tank 21. . In this configuration as well, when the urea water is sucked back after the engine is stopped, the urea water pump 22 is driven to rotate in the reverse direction while the urea water addition valve 80 is kept closed (energized OFF). As a result, air is introduced from the outside into the urea water addition valve 80 through the intake valve 102 and the urea water pipe 101, and the urea water addition valve 80 and the urea water supply pipe 23 ride on the flow of the external air (air flow). The residual urea water is sucked back and collected in the urea water tank 21 (same as in FIG. 9).

  Further, as shown in FIG. 11, a pressure adjusting valve (pressure adjusting device) 103 for adjusting the urea water pressure is connected to the urea water pipe 101 connected to the port portion 94 (see FIG. 8) in the urea water adding valve 80. , And the urea water that is excessive when the pressure is adjusted by the pressure adjusting valve 103 may be discharged into the urea water tank 21. In this case, the pressure adjustment valve 103 itself may be provided in the urea water tank 21, or only the urea water discharge portion (return pipe) of the pressure adjustment valve 103 may be provided in the urea water tank 21. According to this configuration, when urea water is used during engine operation (addition supply to the exhaust pipe 11), part of the urea water supplied to the urea water addition valve 80 is from the outer passage 93 (second passage). It flows to the pressure regulating valve 103 via the urea water pipe 101, and excess urea water is sequentially discharged to the return pipe (not shown) urea water tank 21. Therefore, a flow of urea water from the urea water addition valve 80 to the urea water tank 21 (in other words, circulation of urea water) occurs, and the urea water addition valve 80 can be cooled by the urea water.

  In the above-described embodiment, the urea water pump 22 installed in the urea water tank 21 is configured to be able to rotate forward and backward, and the pump 22 is driven to rotate in the reverse direction, thereby remaining in the urea water addition valve 15 and the urea water supply pipe 23. The urea water is collected in the urea water tank 21, but this may be changed. For example, a urea water pump having two independent pump parts is used, urea water is pumped by one pump part (pumping pump part), and urea water is pumped by the other pump part (suction pump part). Suck back. More specifically, as shown in FIG. 12, the urea water pump 110 is provided with a pumping pump unit 111 and a suction pump unit 112. Each of these pump parts 111 and 112 has a motor drive part individually, and these motor drive parts can rotate only in one direction. Pipes 113 and 114 are connected to the pumping pump unit 111 and the suction pump unit 112, respectively, and a flow path switching device (for example, a flow path switching valve) 115 is provided at the assembly part. A urea water supply pipe 23 is connected to the device 115. The flow path switching device 115 is switched by a control signal from the ECU 30, and in accordance with the switching operation, a state in which the pumping pump unit 111 and the urea water supply pipe 23 communicate with each other, a suction pump unit 112, and urea water Switching to the state where the supply pipe 23 is communicated is performed.

  In the above configuration, during normal engine operation, as shown in FIG. 12A, the flow path switching device 115 is controlled to communicate with the pressure-feed pump unit 111 and the urea water supply pipe 23. The pumping pump unit 111 is controlled to be ON (driven), and the suction pump unit 112 is controlled to be OFF. As a result, the urea water in the urea water tank 21 is supplied to the urea water addition valve through the urea water supply pipe 23. In addition, after the engine is stopped, as shown in FIG. 12B, the flow path switching device 115 is controlled to communicate with the suction pump unit 112 and the urea water supply pipe 23, and the pump for pumping is used. The unit 111 is controlled to be OFF, and the suction pump unit 112 is controlled to be ON (driven). Thereby, the residual urea water such as the urea water supply pipe 23 is collected in the urea water tank 21.

  Also in the configuration of FIG. 12, after the engine is stopped, the urea water pump 110 can be driven in a urea water sucking back state different from the urea water pressure feeding state. It can be recovered in the water tank 21. Thereby, it is possible to prevent the urea water from being frozen in the urea water supply pipe 23 and the like and to protect these components.

  It is also possible to use an air assist type addition valve as the urea water addition valve. Specifically, the compressed air compressed by a compressor (on-vehicle compressor) is guided to a urea water supply system, and urea water is atomized by the compressed air. Incidentally, some large trucks and the like are equipped with an air supply source for adjusting the brake pressure, and it is preferable to use this as an air supply source for air assist.

  At present, the practical application of the urea SCR system for in-vehicle diesel engines is being studied. However, the practical application of the urea SCR system for other engines such as gasoline engines (spark ignition engines) Is possible. Further, the present invention can be similarly applied to an exhaust purification system using a reducing agent other than urea water.

The lineblock diagram showing the outline of the urea SCR system in a 1st embodiment. Sectional drawing which shows the internal structure of a urea water pump. Explanatory drawing which shows the mode of urea water collection | recovery. The flowchart which shows the process sequence of urea water sucking-back control. The block diagram which shows the urea SCR system in 2nd Embodiment. The flowchart which shows the process sequence of urea water sucking-back control in 2nd Embodiment. Explanatory drawing which shows the mode of urea water collection | recovery in 2nd Embodiment. Sectional drawing which shows the structure of the urea water addition valve in 3rd Embodiment. Explanatory drawing which shows the mode of urea water collection | recovery in 3rd Embodiment. Explanatory drawing which shows the mode of urea water collection | recovery in another embodiment. Explanatory drawing which shows the mode of urea water collection | recovery in another embodiment. Explanatory drawing explaining schematic structure of a system in another embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe, 12 ... DPF, 13 ... SCR catalyst (exhaust purification catalyst), 15 ... Urea water addition valve (reducing agent addition valve), 21 ... Urea water tank (reducing agent container), 22 ... Urea water pump, DESCRIPTION OF SYMBOLS 23 ... Urea water supply pipe (reducing agent supply pipe), 25 ... Pressure regulating valve, 30 ... ECU, 71 ... Branch pipe, 72 ... Intake valve, 80 ... Urea water addition valve, 86a, 88a ... Urea water passage (1st (Passage), 88b ... tip addition port, 93 ... outer passage (second passage), 95 ... intake valve, 101 ... urea water piping, 102 ... intake valve, 103 ... pressure regulating valve, 110 ... urea water pump, 111 ... pressure feed Pump part 112, suction pump part 115, flow path switching device.

Claims (4)

A reducing agent container for storing a liquid reducing agent, a pump for pumping the reducing agent in the reducing agent container, and a reducing agent addition valve provided upstream of the exhaust purification catalyst in the exhaust passage of the engine. And supplying a reducing agent pumped from the pump through the reducing agent passage into the exhaust passage by the reducing agent addition valve so that the exhaust purification catalyst performs a specific exhaust purification reaction based on the addition of the reducing agent. In the exhaust emission control device of the engine that is promoted,
A check valve that is provided in a branch passage that branches from the reducing agent passage and is opened due to a pressure difference with the outside when the pressure in the branch passage is reduced, and the opening allows the reducing agent passage to communicate with the outside of the passage. An intake valve comprising:
Sucking back control means for driving the pump in a reducing agent sucking back state different from the reducing agent pumping state after stopping the engine;
The engine exhaust gas purification apparatus, wherein when the pump is driven in a reducing agent sucking back state, the intake valve is opened, and air is introduced into the reducing agent passage from the outside through the branch passage . The suck back control means includes
A first means for closing the reducing agent addition valve and driving the pump in a reducing agent sucking state after the engine is stopped;
Next, a second means for opening the reducing agent addition valve and driving the pump in a reducing agent pumping state;
An exhaust emission control device for an engine according to claim 1 . The suck back control means, said second means subsequently to by the processing, according to the reducing agent addition valve in claim 2, further comprising a third means for driving in a state suck back reducing agent the pump with a closed Engine exhaust purification system. The reducing agent is an aqueous urea solution, and the exhaust purification catalyst promotes the NOx reduction reaction by setting the NOx reduction reaction in which NOx is reduced by ammonia generated from the aqueous urea solution as the exhaust purification reaction. The engine exhaust gas purification apparatus according to any one of 1 to 3 .

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