JP4894827B2 - Reducing agent supply system - Google Patents

Description

  The present invention relates to a reducing agent supply system, and more particularly to a reducing agent supply system that adds a reducing agent to a predetermined reducing agent addition location such as an upstream portion of a NOx catalyst in an exhaust pipe. For example, this system has been put into practical use as a urea SCR (Selective Catalytic Reduction) system in which a urea aqueous solution is added upstream of a selective reduction type NOx catalyst provided in an exhaust pipe of an engine.

  A urea SCR system is known as an exhaust purification system for in-vehicle engines (particularly diesel engines). That is, in the urea SCR system, a selective reduction type NOx catalyst is provided in the exhaust pipe, and a urea water addition valve for adding urea water (urea aqueous solution) as a NOx reducing agent into the exhaust pipe is provided upstream thereof. ing. In this system, the urea water in the urea water tank is supplied to the urea water addition valve through the pipe by driving the pump, and the urea water is added to the exhaust pipe by the urea water addition valve, so that the exhaust gas is exhausted on the NOx catalyst. NOx therein is selectively reduced and removed. When NOx is reduced, urea water is hydrolyzed by exhaust heat to produce ammonia (NH3), which is adsorbed on the NOx catalyst and undergoes a reduction reaction based on ammonia on the NOx catalyst. As a result, NOx is reduced and purified.

The urea water used as the reducing agent freezes at, for example, -11 ° C., and the piping is blocked by the freezing, resulting in a problem that the urea water cannot be supplied immediately after the next engine start. Moreover, since the volume increases due to the freezing of urea water, there is a concern about damage to the piping. Therefore, as a countermeasure against freezing of the urea water, a technique has been proposed in which the urea water in the pipe is sucked back to the tank side by driving the pump in a reverse rotation after the operation of the engine is stopped (see, for example, Patent Document 1). According to such a technique, it is said that freezing of residual urea water in the piping can be suppressed after the engine is stopped.
JP 2008-101564 A

  However, as described above, the urea water existing in the pipe, the urea water addition valve, etc. is completely sucked back even if the urea water in the pipe is sucked back to the tank side by driving the pump reversely after the engine is stopped. Instead, a part of the urea water remains in the piping, the urea water addition valve, or the like. In this case, if the piping is closed due to freezing of the urea water remaining in the piping, the urea water addition valve, etc., it is considered that the problem that urea water cannot be supplied immediately after the next engine start still occurs.

  The main object of the present invention is to provide a reducing agent supply system capable of suitably adding and supplying a reducing agent to the reduction reaction apparatus from the beginning when the pump is started.

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

  In the reducing agent supply system of the present invention, when the reducing agent is added to the predetermined reduction reaction apparatus, the reducing agent in the reducing agent tank is fed to the reducing agent addition means via the reducing agent pipe by driving the pump, The reducing agent is added by the agent adding means. Further, after the supply of the reducing agent to the reducing agent adding means is stopped, a reducing agent discharge process for discharging the reducing agent in the reducing agent pipe is performed. In such a case, after the reducing agent discharge process is performed, the reducing agent remains in the reducing agent pipe or the like in a relatively small amount. For this reason, it is considered that the reducing agent path is blocked due to the freezing of the residual reducing agent, and that the reducing agent is poorly fed when the pump is started next time (that is, when the reducing agent is fed).

In this regard, in the first configuration , the residual reducing agent in the pipe or the like after the reducing agent discharge processing is accumulated in a predetermined place in the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means, In addition, when the pump is started up next time, a supply structure is provided that enables the supply of the reducing agent from the reducing agent tank to the reducing agent addition means even if the residual reducing agent is in a frozen state. Thus, even if the reducing agent remains after the reducing agent discharge processing and further freezes, it is possible to suppress the occurrence of poor feeding of the reducing agent at the next start of the pump. As a result, when the pump is started, the reducing agent can be suitably added and supplied to the reduction reaction apparatus from the beginning.

  The reducing agent discharge process is a process of discharging the reducing agent by sucking back (recovering) the reducing agent from the reducing agent addition unit to the reducing agent tank side, or a reduction from the reducing agent addition unit to the reduction reaction device side. The process of discharging the reducing agent by ejecting the agent is included.

In the second configuration , as the feeding structure, the reducing agent that accumulates the residual reducing agent after the reducing agent discharge processing is provided at the lowest position in the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means. A reservoir is provided. In the reducing agent reservoir, when the residual reducing agent is frozen, the reducing agent path on the reducing agent tank side and the reducing agent path on the reducing agent adding means side communicate with each other through an empty space in the reducing agent reservoir. Is done. Note that the reducing agent reservoir corresponds to a “predetermined location” of the first configuration (the same applies to the sixth configuration and the eighth configuration described later).

  According to the above configuration, after the reducing agent discharge process is performed, the residual reducing agent is stored in the reducing agent reservoir at the lowest position of the reducing agent path by gravity. In such a case, in the reducing agent reservoir, even if the residual reducing agent is frozen, the reducing agent can be distributed from the reducing agent tank to the reducing agent adding means using the empty space. Therefore, even when the pump is started after the reducing agent is in a frozen state, it is possible to suppress the occurrence of defective feeding of the reducing agent at the beginning of the starting.

Here, - reducing agent reservoir are those vertical height dimension of the opening section is larger than the opening diameter and good (third configuration) of the other pipe section. In this case, in the configuration in which the residual reducing agent is stored in the reducing agent reservoir, an empty space can be easily secured in the upper part in the reducing agent reservoir.

Also, - reducing agent reservoir, the top is narrow its opening cross-section, may lower is formed wider (fourth configuration). In this case, in the configuration in which the residual reducing agent is stored in the reducing agent reservoir, an empty space can be easily secured in the upper part in the reducing agent reservoir. In addition, as described above, the shape of the opening cross section having a narrow upper portion and a lower lower portion ensures a sufficient storage space for the residual reducing agent while minimizing the area of the opening cross section of the reducing agent reservoir. Can be suppressed. This is an advantageous configuration for suitably distributing the reducing agent when the reducing agent reservoir portion constitutes a part of the reducing agent path.

In the fifth configuration , the high-order portion of the reducing agent reservoir is connected to a feed flow passage that feeds the reducing agent from the tank side to the reducing agent addition means, and the low-order portion of the reducing agent reservoir is A discharge flow path portion for discharging the reducing agent from the reducing agent reservoir when the reducing agent discharge process is performed is connected.

  According to the above configuration, at the time of normal reducing agent feeding (at the time of feeding to the reducing agent adding means side), the reducing agent is fed through the feed channel portion connected to the higher portion (upper part) of the reducing agent reservoir. On the other hand, when the reducing agent is discharged, the reducing agent is discharged through the discharge channel connected to the lower part (lower part) of the reducing agent reservoir. In this case, after the reducing agent discharge process is performed, a predetermined empty space is secured above the discharge flow path in the reducing agent reservoir, and the feed flow path is communicated with the empty space. Thereby, even when the residual reducing agent is frozen, the reducing agent can be circulated through the feed flow path portion at the next start of the pump.

In the sixth configuration , as a feeding structure, an upper pipe portion and a lower pipe portion provided by branching a part of the reducing agent pipe from the outlet portion of the reducing agent tank to the reducing agent addition means into two upper and lower systems. The lower piping part is provided at the lowest position in the middle of the reducing agent path from the outlet part of the reducing agent tank to the reducing agent addition means, and stores a reducing agent reservoir for collecting the residual reducing agent after the reducing agent discharge process is performed. Has become a department. Further, the upper piping portion becomes an empty space after the reducing agent discharge processing is performed, and becomes a route communication portion that connects the reducing agent route on the reducing agent tank side and the reducing agent route on the reducing agent addition means side. Yes.

  According to the above configuration, during normal reducing agent feeding (at the time of feeding to the reducing agent adding means), the reducing agent is circulated through at least one of the upper and lower two reducing agent pipes. Further, when the reducing agent discharge process is performed after the supply of the reducing agent is stopped, the reducing agent remains in the lower pipe among the two upper and lower reducing agent pipes, and an empty space (color) is left in the upper pipe. In this case, even if the residual reducing agent is frozen, the reducing agent can be circulated through the upper pipe when the pump is started next time. Therefore, it is possible to suppress the occurrence of poor supply of the reducing agent at the beginning of pump activation.

Here, the lower piping section may have a larger opening cross section than the upper piping section (seventh configuration) . According to this configuration, it is possible to minimize the area of the opening cross section of the reducing agent path that leads from the tank side to the reducing agent addition means side while ensuring a sufficient storage space for the residual reducing agent. This is an advantageous configuration for suitably distributing the reducing agent when two systems of reducing agent paths are configured by the upper piping portion and the lower piping portion.

On the other hand, in the eighth configuration , the feeding structure is provided at the lowest position in the middle of the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means, and the residual reducing agent after the reducing agent discharge processing is performed. And a heating means for heating the residual reducing agent accumulated in the reducing agent reservoir when the supply of the reducing agent at the next start of the pump is started.

According to the eighth configuration , after the reducing agent discharge process is performed, the residual reducing agent is stored in the reducing agent reservoir at the lowest position of the reducing agent path by gravity. In such a case, even if the residual reducing agent accumulated in the reducing agent reservoir is frozen, it is thawed by heating of the heating means at the next pump activation. Therefore, even when the pump is started after the reducing agent is in a frozen state, it is possible to suppress the occurrence of defective feeding of the reducing agent at the beginning of the starting. In particular, in this configuration, since only the reducing agent reservoir needs to be heated, an effect of minimizing the heating target can be obtained.

Here, - reducing agent reservoir, the reducing agent may as those having a volume greater than the predicted residual amount of the reducing agent after the implementation of the discharge process (ninth configuration). Thereby, even when the residual reducing agent is stored in the reducing agent reservoir, it is possible to secure an empty space in the upper part of the reducing agent reservoir.

  In addition, since there is an increase in volume when the reducing agent is frozen, it is preferable that the reducing agent reservoir has a volume that allows for the increase in volume during freezing. The predicted residual amount of reducing agent is preferably determined in advance for each system.

As the reducing agent supply system of the present invention, one that is applied to an exhaust purification device using a NOx catalyst such as a selective reduction type NOx catalyst is known ( tenth configuration ). In this case, the reducing agent is added to the upstream side of the NOx catalyst in the exhaust passage, and NOx purification suitable for the NOx catalyst is performed by the added reducing agent.

(First embodiment)
Hereinafter, an embodiment of an exhaust gas purification system embodying the present invention will be described with reference to the drawings. The exhaust purification system of the present embodiment purifies exhaust of a diesel engine mounted on an automobile, and is constructed as a so-called urea SCR system that purifies NOx in exhaust using a selective reduction catalyst. 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. FIG. 1 is a view of the present system as viewed from the horizontal direction in a state where it is mounted on an automobile. In the figure, X indicates the horizontal direction and Y indicates the vertical direction.

  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 liquid reducing agent into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11. Actually, the exhaust pipe 11 is configured by connecting a plurality of pipe materials, but here, the exhaust pipe 11 is collectively referred to as the exhaust pipe 11.

  In the present embodiment, the pipe portion between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11 is configured by a bent pipe bent in a crank shape up and down, and a urea water addition valve 15 is provided at an outer portion of the bent pipe. It is arranged. The urea water addition valve 15 extends in a substantially horizontal direction, and is provided in a direction in which the tip ejection portion 15 a faces the SCR catalyst 13.

  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 NOx concentration in exhaust gas (and consequently the NOx purification rate by the SCR catalyst 13) and the exhaust gas temperature are detected. Although not shown, 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 required further downstream of the exhaust pipe 11. It is provided according to.

  The DPF 12 is a PM removal filter that collects PM (particulate matter) in the 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 reduction reaction (exhaust gas purification reaction) of NOx. For example, 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 supplies ammonia (NH3) 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 an electromagnetic on-off valve provided with a drive unit composed of an electromagnetic solenoid or the like, a urea water passage through which urea water flows, and a valve body unit having a needle for opening and closing the tip ejection unit 15a. It is comprised and opens or closes based on the drive signal from ECU40. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and urea water is added (injected) from the tip ejection portion 15a as the needle moves.

  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. In the following, for convenience of explanation, the tank side is described as the upstream side and the urea water addition valve side as the downstream side, based on the case where urea water is supplied from the urea water tank 21 to the urea water addition valve 15.

  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.

  The urea water tank 21 and the urea water addition valve 15 are connected by a urea water pipe 22, and a urea water pump 23 is provided in the middle of the urea water pipe 22. A urea water passage (reducing agent passage) is formed in the urea water pipe 22. The urea water pump 23 is an in-line electric pump that is rotationally driven by a drive signal from the ECU 40, and can rotate in either the forward or reverse direction. When the urea water pump 23 is rotationally driven in a predetermined forward rotation direction, the urea water in the urea water tank 21 is pumped up and discharged (pressure-fed) to the urea water addition valve 15 side through the urea water pipe 22. Further, when the urea water pump 23 is rotationally driven in the reverse rotation direction, urea water is sucked back through the urea water pipe 22 from the urea water addition valve 15 side. In this embodiment, since the urea water pump 23 is provided outside the urea water tank 21, that is, without being immersed in the urea water, the urea water pump 23 can be prevented from being damaged due to freezing and expansion of the urea water. ing.

  Further, in the middle of the urea water pipe 22, a flow adjusting device 30 having a urea water reservoir portion 31 that is a portion having an opening cross section larger than that of the urea water pipe 22 is provided. The details will be described later.

  As another configuration of the urea water supply system, the urea water pipe 22 includes a pressure sensor 25 for detecting the pressure of the urea water in the urea water pipe 22 and a temperature sensor 26 for detecting the temperature of the urea water. And are provided.

  In the system, the ECU 40 is a part that mainly performs control related to exhaust gas purification as an electronic control unit. The ECU 40 includes a known microcomputer (not shown), and detection signals from the exhaust sensor 16, the pressure sensor 25, and the temperature sensor 26 are sequentially input to the ECU 40. The ECU 40 performs various controls relating to exhaust gas purification by operating various actuators including the urea water addition valve 15 in a desired manner based on the detection values of these various sensors. Specifically, for example, by controlling the energization time of the urea water addition valve 15 and the drive amount of the urea water pump 23, 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 operation of the engine, the urea water in the urea water tank 21 is pumped to the urea water addition valve 15 through the urea water pipe 22 by driving the urea water pump 23, and the urea water addition valve 15 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)
In this reaction, urea water is hydrolyzed by exhaust heat to generate ammonia (NH3), and ammonia is adsorbed to the SCR catalyst 13 and the NOx in the exhaust is selectively absorbed by ammonia in the SCR catalyst 13. Reduced and removed. That is, NOx is reduced and purified by performing a reduction reaction based on the ammonia (the above reaction formulas (Formula 1) to (Formula 3)) on the SCR catalyst 13.

  By the way, in this embodiment, after the urea water pump 23 is stopped when the engine is stopped, as a urea water discharge process, the urea water is sucked back from the urea water addition valve 15 side to the urea water pump 23 side. Processing (collection processing) is performed. This sucking back process is performed by driving the urea water pump 23 in reverse rotation after the engine is stopped, and the urea water in the urea water pipe 22 is sucked into the urea water tank 21 by driving the urea water pump 23 in reverse rotation. Returned (collected). By this sucking-back process, breakage of the urea water pipe 22 due to freezing and expansion of the residual urea water in the urea water pipe 22 is suppressed.

  Supplementally, a branch pipe 36 is provided in the urea water addition valve 15 (or the urea water pipe 22 in the vicinity thereof), and an air suction valve 37 is provided in the branch pipe 36. The air intake valve 37 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 this system, the urea water pump 23 rotates in reverse (urea water after the engine is stopped). The air suction valve 37 is opened by the negative pressure in the urea water pipe 22 when it is driven in the sucking back state, and air is introduced from the outside. An electromagnetic on-off valve is used as the air intake valve 37, and the air intake valve 37 is electrically opened when the urea water pump 23 is driven in the reverse rotation (urea water sucking back state) after the engine is stopped. It is also possible.

  After the urea water sucking-back process is performed, the urea water remains in the urea water pipe 22 or the like, although it is a relatively small amount. Therefore, it is considered that the urea water path is closed due to the freezing of the residual urea water, and the urea water supply failure occurs at the next pump start-up (that is, when the urea water supply starts).

  Therefore, in this embodiment, the flow adjusting device 30 is provided in the middle of the urea water pipe 22 as a countermeasure against freezing of the residual urea water after the urea water sucking back process is performed. The distribution adjusting device 30 corresponds to a “feeding structure”. As shown in FIG. 1, the flow adjusting device 30 includes a urea water reservoir 31 that accumulates residual urea water after the urea water suck-back process, and a flow path switching unit 32 that is provided on the tank side of the urea water reservoir 31. And two piping parts 33 and 34 provided in parallel between the urea water reservoir 31 and the flow path switching part 32.

  The urea water reservoir 31 is a storage container provided at the lowest position in the middle of the urea water path from the outlet portion of the urea water tank 21 (that is, the connection portion between the tank 21 and the pipe 22) to the urea water addition valve 15, After the urea water sucking back process is performed, urea water remaining in the urea water pipe 22 or the like, in other words, urea water that has not been sucked back is stored in the urea water reservoir 31 by gravity. The urea water reservoir 31 has a volume that is larger than the predicted residual amount of urea water (the amount of urea previously determined by experiments or the like) after the urea water suction process is performed. The upstream urea water pipe 22 and the downstream urea water pipe 22 connected to the urea water reservoir 31 are both provided in a direction extending in the vertical direction, whereby the urea water reservoir 31 is installed at a low position. It has become. In addition, the urea water pool part 31 should just be installed so that the bottom face inside the container may become lower than another site | part.

  The urea water reservoir 31 has a larger vertical dimension in the opening cross section than the opening diameter of other pipe parts (such as the urea water pipe 22). More specifically, the opening cross section of the urea water reservoir 31 has the shape shown in FIG. 2 (cross sectional view taken along the line AA in FIG. 1), and the height dimension H is the opening diameter of the urea water pipe 22 and the like ( (Not shown). Further, as can be seen from FIG. 2 (a), the urea water reservoir 31 has a narrow upper portion (a portion that is above the gravitational direction in the installed state) and a lower portion (a portion that is below the gravitational direction in the installed state). Is formed wide.

  Note that the cross-sectional shape of the urea water reservoir 31 is not limited to that shown in the figure, and if the upper part of the opening cross-section is narrow and the lower part is wide, it has a substantially L shape or a substantially triangular shape. The thing etc. may be sufficient.

  Also, one of the two piping parts 33, 34 is configured such that urea water is supplied when urea water flows from the urea water tank 21 side to the urea water addition valve 15 side, that is, when urea water is added by the urea water addition valve 15. The other piping section 34 is configured to distribute urea water when urea water flows from the urea water addition valve 15 side to the tank 21 side, that is, when urea water is sucked back. This is a piping part to be circulated (hereinafter referred to as a suck-back piping part 34). The feed pipe section 33 is connected to the higher portion of the urea water reservoir 31 on the downstream side (urea water addition valve 15 side), whereas the suction pipe section 34 is connected to the downstream side (urea water addition valve 15). Side) is connected to the lower portion of the urea water reservoir 31.

  The flow path switching unit 32 is an electromagnetic flow path switching valve that switches which of the two piping parts 33 and 34 communicates with the urea water piping 22 on the upstream side, and is switched by the ECU 40. In this case, when the urea water is added by the urea water addition valve 15, the feed pipe portion 33 is communicated with the urea water pipe 22, and when the urea water is sucked back, the suck back pipe portion 34 is communicated with the urea water pipe 22. .

  Next, the operation when urea water is added and sucked back will be described with reference to FIG. In FIG. 3, (a) shows the state when urea water is added, and (b) shows the state after sucking back urea water. The hatched portion in the figure indicates the presence of urea water.

  At the time of urea water addition shown in FIG. 3A, the urea water pump 23 is driven to rotate forward, and the urea water in the urea water tank 21 is fed to the urea water addition valve 15 side through the urea water pipe 22. At this time, the entire urea water path from the outlet portion of the urea water tank 21 to the urea water addition valve 15 is filled with urea water.

  On the other hand, after the urea water sucking back shown in FIG. 3 (b), the urea water pump 23 is driven in the reverse rotation, and urea existing in the urea water addition valve 15, the urea water pipe 22, the urea water reservoir 31 and the like. Water is sucked back to the urea water tank 21 side through the suck-back piping section 34. At this time, the urea water remaining in the pipe and the like without being sucked back flows into the urea water reservoir 31 at the lowest position as shown in the figure, and is accumulated in the urea water reservoir 31. In this case, since the urea water reservoir 31 has a volume larger than the predicted residual amount of urea water, even if the residual urea water is accumulated in the urea water reservoir 31, an empty space S is formed inside the urea water reservoir 31 as shown in the figure. Is secured. For the empty space S in the urea water reservoir 31, see also FIG. In this state, the urea water path on the tank 21 side and the urea water path on the urea water addition valve 15 side are in communication with each other by the empty space S in the urea water reservoir 31.

  Even if the vehicle is left after the state shown in FIG. 3 (b) and the remaining urea water freezes thereafter, the urea water path on the tank 21 side further than that due to the empty space S in the urea water reservoir 31. And the urea water path on the urea water addition valve 15 side are kept in communication with each other. Therefore, when the urea water pump 23 is started as the engine is started in a state where the residual urea water is frozen, the urea water is supplied and exhausted from the urea water tank 21 to the urea water addition valve 15 from the start. The urea water can be added into the pipe 11.

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

  A urea water reservoir 31 for collecting residual urea water after sucking back urea water is provided at the lowest position in the middle of the urea water path from the tank outlet to the urea water addition valve 15, and the urea water reservoir 31 is a residual urea water. In the frozen state, the urea water path on the tank side and the urea water path on the urea water addition valve 15 side are communicated with each other through the empty space S. According to this configuration, in the urea water reservoir 31, even if the residual urea water freezes after the urea water is sucked back, the urea water is circulated from the urea water tank 21 to the urea water addition valve 15 using the empty space S. It becomes possible. Therefore, even when the pump is started (when the engine is started) after the urea water is frozen, it is possible to suppress the occurrence of poor feeding of the urea water at the beginning of the startup. As a result, urea water can be suitably added and supplied to the SCR catalyst 13 of the exhaust pipe 11 from the beginning when the pump is started.

  If urea water can be suitably added and supplied to the SCR catalyst 13 as described above, NOx purification by the SCR catalyst 13 can be performed appropriately.

  The urea water reservoir 31 has a larger vertical dimension in the opening cross section than the opening diameter of the other pipe portions, and the upper portion of the opening cross section is narrow and the lower portion is wide. In the configuration in which the residual urea water is stored in the part 31, the empty space S can be easily secured in the upper part in the urea water storage part 31. Moreover, the area of the opening cross section of the urea water reservoir 31 can be minimized while ensuring a sufficient storage space for the residual urea water. This is an advantageous configuration for suitably distributing the urea water when the urea water reservoir 31 forms part of the urea water path.

  A feed pipe portion 33 that feeds urea water from the urea water tank 21 side to the urea water addition valve 15 side is connected to the higher portion of the urea water reservoir portion 31 and the urea water reservoir portion 31 is connected to the lower portion when the urea water is sucked back. The suction pipe 34 for sucking urea water from the pipe is connected. Thus, it is natural that the urea water supply can be suitably realized during normal addition of the urea water. After the urea water is sucked back, a predetermined empty space above the sucking-back pipe portion 34 in the urea water reservoir 31. S can be secured, and the feed pipe section 33 can be communicated with the empty space S. Thereby, even if the residual urea water is frozen while the engine is stopped, the urea water can be circulated through the feed pipe section 33 at the next pump activation.

  Since the urea water reservoir 31 has a volume larger than the predicted residual amount of urea water after the urea water is sucked back, an empty space S is formed above the urea water reservoir 31 even when the residual urea water is accumulated. It can be secured.

(Second Embodiment)
Next, a second embodiment of the present invention will be described focusing on differences from the first embodiment. In the present embodiment, a configuration in which a part of the urea water pipe 22 is used as a urea water reservoir will be described.

  FIG. 4 is a diagram showing the configuration of the urea water supply system in the present embodiment. In FIG. 4, as in FIG. 1, X in the figure indicates the horizontal direction, and Y indicates the vertical direction.

  As shown in FIG. 4, a part of the urea water pipe 22 is most in the middle of the urea water path from the outlet part of the urea water tank 21 (that is, the connection part between the tank 21 and the pipe 22) to the urea water addition valve 15. It is formed so as to be lower, and its lowest position is the urea water reservoir 51. In the urea water reservoir 51, the urea water remaining in the urea water pipe 22 and the like, in other words, the urea water that could not be sucked back after the urea water sucking back process is stored by gravity. Yes.

  The urea water reservoir 51 has a volume larger than the predicted residual amount of urea water after the urea water sucking-back process is performed, and is installed in the vehicle in a horizontal direction. In addition, the urea water reservoir 51 is configured by a pipe having a height dimension of an opening cross section that is larger than the opening diameter of the other pipe part (urea water pipe 22). More specifically, the opening cross section of the urea water reservoir 51 is, for example, an ellipse, and is installed so that its major axis is up and down (up and down in the direction of gravity). For example, the major axis is preferably twice or twice or more than the minor axis. In addition, it is also possible to use a circular pipe having a larger diameter than the other pipe part (urea water pipe 22) as the urea water reservoir 51. However, the urea water reservoir 51 can be configured by the same pipe as the other pipe parts (urea water pipe 22).

  Next, the operation when urea water is added and sucked back will be described with reference to FIG. In FIG. 5, (a) shows the state when urea water is added, and (b) shows the state after sucking back urea water. The hatched portion in the figure indicates the presence of urea water.

  At the time of urea water addition shown in FIG. 5A, the urea water pump 23 is driven to rotate forward, and the urea water in the urea water tank 21 is fed to the urea water addition valve 15 side through the urea water pipe 22. At this time, the entire urea water path from the outlet portion of the urea water tank 21 to the urea water addition valve 15 is filled with urea water.

  On the other hand, after the urea water sucking back shown in FIG. 5 (b), the urea water pump 23 is driven in reverse rotation, and the urea water existing in the urea water addition valve 15 and the urea water pipe 22 is moved to the urea water tank 21 side. Sucked back. At this time, the urea water remaining in the piping and the like without being sucked back is accumulated in the urea water reservoir 51 as shown in the figure. In this case, since the urea water reservoir 51 has a volume larger than the predicted residual amount of urea water, even if residual urea water is accumulated in the urea water reservoir 51, an empty space S is formed inside the urea water reservoir 51 as shown in the figure. Is secured. In this state, the urea water path on the tank 21 side and the urea water path on the urea water addition valve 15 side are in communication with each other due to the empty space S in the urea water reservoir 51. Moreover, even if the residual urea water freezes, the empty space S is secured. Therefore, when the urea water pump 23 is started as the engine is started in a state where the residual urea water is frozen, the urea water is supplied and exhausted from the urea water tank 21 to the urea water addition valve 15 from the start. The urea water can be added into the pipe 11.

  As described above, also in the second embodiment, urea water is suitably added and supplied to the SCR catalyst 13 of the exhaust pipe 11 from the beginning when the pump is started (when the engine is started), as in the first embodiment. Can do.

(Third embodiment)
In the present embodiment, as a difference from the above-described embodiments, a part of the urea water pipe 22 from the outlet portion of the urea water tank 21 to the urea water addition valve 15 is branched into two upper and lower systems. FIG. 6 is a diagram showing the configuration of the urea water supply system in the present embodiment. In FIG. 6, as in FIG. 1, X in the figure indicates the horizontal direction and Y indicates the vertical direction.

  In FIG. 6, the urea water pipe 22 branches into two upper and lower systems in the middle of the urea water path from the outlet portion of the urea water tank 21 (that is, the connection portion between the tank 21 and the pipe 22) to the urea water addition valve 15. Of these, the upper pipe part 53 is above and the lower pipe part 54 is below. The lower piping part 54 is provided at the lowest position in the middle of the urea water path from the outlet part of the urea water tank 21 to the urea water addition valve 15. The lower piping part 54 sucks back urea water. After the treatment, the urea water remaining in the urea water pipe 22 or the like, in other words, the urea water that could not be sucked back is stored by gravity. The lower piping part 54 has a volume larger than the predicted residual amount of urea water after the urea water sucking-back process is performed.

  Further, the upper piping portion 53 is provided at substantially the same height as the urea water addition valve 15 and becomes an empty space after the urea water is sucked back, and the urea water path and the urea water addition valve 15 on the tank 21 side than that. The urea water path on the side is communicated. The upper piping portion 53 corresponds to a “path communication portion”, the lower piping portion 54 corresponds to a “reducing agent reservoir portion”, and each of the piping portions 53 and 54 corresponds to a “feeding structure”.

  In this embodiment, the upper side piping part 53 and the lower side piping part 54 are comprised using the same piping as another piping part. However, different piping may be used for the upper piping portion 53 and the lower piping portion 54, and in this case, a lower piping portion 54 having a larger opening cross section than the upper piping portion 53 may be used.

  Next, the operation when urea water is added and sucked back will be described with reference to FIG. In FIG. 7, (a) shows a state when urea water is added, and (b) shows a state after sucking back urea water. The hatched portion in the figure indicates the presence of urea water.

  At the time of urea water addition shown in FIG. 7A, the urea water pump 23 is driven to rotate forward, and the urea water in the urea water tank 21 is fed to the urea water addition valve 15 side through the urea water pipe 22. At this time, the entire urea water path (including the upper pipe portion 53 and the lower pipe portion 54) from the outlet portion of the urea water tank 21 to the urea water addition valve 15 is filled with urea water.

  Incidentally, at the time of urea water addition, the structure which distribute | circulates urea water through either one of the upper side piping part 53 and the lower side piping part 54 may be sufficient. For example, a flow path switching device is provided at the upstream branch portion of both the piping sections 53 and 54, and urea water is circulated through only one of the both piping sections 53 and 54 by switching operation of the flow path switching apparatus.

  On the other hand, after the urea water sucking back shown in FIG. 7B, the urea water pump 23 is reversely driven, and the urea water existing in the urea water addition valve 15 and the urea water pipe 22 is moved to the urea water tank 21 side. Sucked back. At this time, urea water remaining in the piping and the like without being sucked back is accumulated in the lower piping portion 54 as shown in the figure. In such a case, since the lower piping part 54 has a volume larger than the predicted residual amount of urea water, even if residual urea water accumulates in the lower piping part 54, an empty space in the upper piping part 53 as shown in the figure. S is secured. In this state, the urea water path on the tank 21 side and the urea water path on the urea water addition valve 15 side are more communicated with each other by the empty space S in the upper piping portion 53. Moreover, even if the residual urea water freezes, the empty space S is secured. Therefore, when the urea water pump 23 is started as the engine is started in a state where the residual urea water is frozen, the urea water is supplied and exhausted from the urea water tank 21 to the urea water addition valve 15 from the start. The urea water can be added into the pipe 11.

  As described above, in the third embodiment as well, similarly to the first embodiment, when the pump is started (when the engine is started), urea water is preferably added and supplied to the SCR catalyst 13 of the exhaust pipe 11 from the beginning. be able to.

  When the lower pipe portion 54 is configured to have a larger opening cross section than the upper pipe portion 53, a urea water addition valve is provided from the urea water tank 21 side while ensuring a sufficient storage space for residual urea water. The area of the opening cross section of the urea water path leading to the 15 side can be minimized. This is an advantageous configuration for suitably distributing the urea water when two systems of urea water paths are constituted by the upper and lower pipe sections 53 and 54.

(Fourth embodiment)
In this embodiment, when the residual urea water collected in the urea water reservoir is in a frozen state, a configuration is adopted in which the urea water in the frozen state is thawed by heating of the heating means. FIG. 8 is a diagram showing a configuration of a urea water supply system in the present embodiment. In FIG. 8, similarly to FIG. 1, X in the figure indicates the horizontal direction and Y indicates the vertical direction. The hatched portion in the figure indicates the presence of urea water.

  In FIG. 8, a part of the urea water pipe 22 is at the lowest position in the middle of the urea water path from the outlet part of the urea water tank 21 (that is, the connection part between the tank 21 and the pipe 22) to the urea water addition valve 15. The lower portion is the urea water reservoir 61. In the urea water reservoir 61, the urea water remaining in the urea water pipe 22 and the like, that is, the urea water that could not be completely sucked back after the urea water sucking back process is stored by gravity. Yes.

  Here, a configuration in which a part of the urea water pipe 22 is the urea water reservoir 61 is the same as in FIG. 4 and the like, but in this embodiment, an “empty space S” is formed in the urea water reservoir 61. Instead of the configuration, the urea water reservoir 61 is filled with the residual urea water as in the hatched portion shown in the figure.

  A heating device 62 is provided so as to surround the urea water reservoir 61. The heating device 62 contains the antifreeze liquid and is provided around the urea water reservoir 61, the magnetron 64 that irradiates the antifreeze liquid in the antifreeze liquid container 63 with microwaves, and the temperature of the antifreeze liquid in the antifreeze liquid container 63. And a temperature sensor 65 for detecting. The detection result of the temperature sensor 65 is input to the ECU 40, and the ECU 40 controls the driving of the magnetron 64 based on the input.

  FIG. 9 is a flowchart showing a heating process of urea water at the time of starting the engine, and this process is started by the ECU 40 in accordance with a predetermined engine starting operation such as an ON operation of an ignition switch.

  In FIG. 9, first, in step S11, it is determined whether or not the antifreeze liquid temperature is equal to or lower than a predetermined value K1. The predetermined value K1 is determined based on the freezing temperature of residual urea water (−11 ° C.). For example, K1 is “−11 ° C.” or “−11 ± α ° C.”. If step S11 is YES, it will progress to subsequent step S12, and if it is NO, this process will be complete | finished as it is. In step S12, a drive signal is output to the magnetron 64 of the heating device 62 to irradiate the antifreeze with microwaves. That is, the antifreeze liquid temperature is raised by the microwave irradiation, and the residual urea water is thawed by heating the urea water reservoir 61 from the surroundings.

  Thereafter, in step S13, it is determined whether or not the antifreeze liquid temperature has risen to a predetermined value K2 or more. K2 ≧ K1, for example, K2 = K1. If it is YES, it will progress to subsequent step S14, and if it is NO, it will return to step S12 and will continue microwave irradiation. In step S14, the microwave irradiation is stopped, and in the subsequent step S15, the start of operation of the urea water pump 23 and the urea water addition valve 15 is permitted. Thereby, the supply of urea water to the exhaust pipe 11 is started after the engine is started.

  As described above, according to the fourth embodiment, the residual urea water in the urea water reservoir 61 is heated when the engine is started, so that the residual urea water in the frozen state is thawed. Therefore, even when the pump is started after the residual urea water is frozen (when the engine is started), it is possible to suppress the occurrence of poor feeding of urea water at the beginning of the startup. In particular, in this configuration, since only the urea water reservoir 61 needs to be heated, an effect of minimizing the heating target can be obtained.

  As described above, the heating unit may be embodied by a heater heating type heating device in addition to the heating unit 62 by the microwave irradiation type heating device 62. Specifically, a heater is provided in the vicinity of the urea water reservoir 61, and energization of the heater is controlled based on the temperature of the residual urea water when the engine is started. For example, when the temperature of the residual urea water is equal to or lower than the urea water freezing temperature (−11 ° C.) at the time of starting the engine, the heater energization is turned on and the heater energization is continued until the urea water temperature becomes equal to or higher than the urea water freezing temperature. To do.

(Other embodiments)
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, when the urea water sucking back process is performed, the air intake valve 37 is mechanically or electrically opened to introduce the external air into the pipe, but this is changed. For example, when the urea water sucking back process is performed, the urea water addition valve 15 may be opened to introduce external air into the pipe.

  In the above embodiment, as the reducing agent discharging process after the engine is stopped, the sucking back process for sucking the urea water back to the urea water tank 21 side from the urea water adding valve 15 is performed. It is good also as a structure which implements the urea water ejection process which ejects urea water in the exhaust pipe 11 from 15. FIG. In this case, in the urea water ejection process, after the engine is stopped, the urea water pump 23 is driven to rotate in the forward direction with the urea water addition valve 15 opened, and the urea water in the urea water pipe 22 and the like is supplied to the urea water addition valve. 15 is discharged from the tip ejection portion 15a. Even in this configuration, urea water remains in a small amount after the urea water ejection process is performed. However, by providing the urea water reservoir 31 or the like in the middle of the urea water pipe 22 as described above, the next time the pump is started (engine start) The urea water can be suitably added at the time. Specifically, the configuration including the urea water reservoir 31 shown in FIG. 1, the configuration including the urea water reservoir 51 shown in FIG. 4, the configuration including the upper piping portion 53 and the lower piping portion 54 shown in FIG. 6, and FIG. Any of the configurations including the urea water reservoir 61 and the heating device 62 shown in the figure can be applied.

  -The piping part (urea water reservoir part 31,51,61, lower piping part 54) used as a reducing agent reservoir part can be comprised by piping which can be expanded-contracted. For example, the reducing agent reservoir is made of a stretchable material (such as a synthetic resin material) or a stretchable shape (such as a bellows). In this case, even if the reducing agent (urea water) remaining in the reducing agent reservoir portion expands due to freezing, the volume increase due to the expansion can be absorbed by deformation of the piping portion.

  It is also possible to provide a plurality of reducing agent reservoirs in the middle of the reducing agent path from the tank outlet to the reducing agent addition means (urea water addition valve 15).

  In the above-described embodiment, the exhaust pipe 11 is configured by a bent pipe that is bent up and down, and the urea water addition valve 15 is provided in the horizontal direction on the outer portion of the bent pipe, but this may be changed. . For example, in the horizontal part of the exhaust pipe 11, the urea water addition valve 15 can be installed downward or upward.

  In the above embodiment, an in-line type electric pump is used as the urea water pump 23. However, it is possible to change this and use an in-tank type electric pump. That is, the structure which provides the urea water pump 23 in the urea water tank 21 is employ | adopted.

  -You may employ | adopt structures other than a urea water addition valve as a reducing agent addition means. For example, as the reducing agent addition means, a configuration may be adopted in which a thin tubular addition nozzle is provided upstream of the SCR catalyst in the engine exhaust pipe, and urea water (reducing agent aqueous solution) is added from the addition nozzle.

  -Besides being put into practical use as a urea SCR system for in-vehicle diesel engines, it can also be put into practical use as a urea SCR system for gasoline engines, particularly lean burn engines. Further, the present invention can be similarly applied to an exhaust purification system using a reducing agent other than urea water. For example, it is conceivable to use an aqueous solution containing ammonia as the reducing agent.

The lineblock diagram showing the outline of the urea SCR system in a 1st embodiment. AA sectional view taken on the line AA of FIG. The figure for demonstrating the operation | movement at the time of addition of urea water and after sucking back. The figure which shows the structure of the urea water supply system in 2nd Embodiment. The figure for demonstrating the operation | movement at the time of addition of urea water and after sucking back. The figure which shows the structure of the urea water supply system in 3rd Embodiment. The figure for demonstrating the operation | movement at the time of addition of urea water and after sucking back. The figure which shows the structure of the urea water supply system in 4th Embodiment. The flowchart which shows the heating process of the urea water at the time of engine starting.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe (exhaust passage), 13 ... SCR catalyst (reduction reaction apparatus, NOx catalyst), 15 ... Urea water addition valve (reducing agent addition means), 21 ... Urea water tank (reducing agent tank), 22 ... Urea water Pipe (reducing agent passage), 23 ... urea water pump, 30 ... flow regulating device (feeding structure), 31 ... urea water reservoir (reducing agent reservoir), 32 ... flow path switching unit, 33 ... feed piping (feed) Flow path part), 34 ... Suction pipe part (discharge flow path part), 51 ... Urea water reservoir part (reducing agent reservoir part), 53 ... Upper pipe part (path communication part), 54 ... Lower pipe part (reducing agent) Reservoir), 61 ... Urea water reservoir (reducing agent reservoir), 62 ... Heating device (heating means), S ... Empty space.

Claims (8)

A reducing agent tank for storing a liquid reducing agent; and a reducing agent adding means connected to the reducing agent tank via a reducing agent pipe for adding and supplying the reducing agent in the tank toward a predetermined reduction reaction device; A pump for feeding the reducing agent to the reducing agent addition means,
A reducing agent supply system for performing a reducing agent discharge process for discharging the reducing agent in the reducing agent pipe after stopping the reducing agent supply to the reducing agent addition means,
Residual reducing agent in the piping after the reducing agent discharge processing is accumulated in a predetermined place in the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means, and the pump is started next time. Sometimes, provided with a feeding structure that enables feeding of the reducing agent from the reducing agent tank to the reducing agent addition means even when the residual reducing agent is in a frozen state ,
As the feeding structure, a reducing agent reservoir for storing the residual reducing agent is provided at the lowest position in the middle of the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means,
The reducing agent reservoir portion is an empty space in the reducing agent reservoir portion between the reducing agent path on the reducing agent tank side and the reducing agent path on the reducing agent addition means side when the residual reducing agent is frozen. A reducing agent supply system characterized in that it communicates with each other. 2. The reducing agent supply system according to claim 1 , wherein the reducing agent reservoir portion has a vertical dimension of an opening cross section larger than an opening diameter of the other pipe portion. 3. The reducing agent supply system according to claim 1 , wherein the reducing agent reservoir is formed such that an upper portion of an opening cross section is narrow and a lower portion is wide. A feeding flow path portion that feeds the reducing agent from the reducing agent tank side to the reducing agent addition means side is connected to the higher portion of the reducing agent reservoir portion, and the lower portion of the reducing agent reservoir portion is connected to the lower portion of the reducing agent reservoir portion. The reducing agent supply system according to any one of claims 1 to 3 , wherein a discharge flow path unit that discharges the reducing agent from the reducing agent reservoir unit is connected when performing the reducing agent discharge process. A reducing agent tank for storing a liquid reducing agent; and a reducing agent adding means connected to the reducing agent tank via a reducing agent pipe for adding and supplying the reducing agent in the tank toward a predetermined reduction reaction device; A pump for feeding the reducing agent to the reducing agent addition means,
A reducing agent supply system for performing a reducing agent discharge process for discharging the reducing agent in the reducing agent pipe after stopping the reducing agent supply to the reducing agent addition means,
Residual reducing agent in the piping after the reducing agent discharge processing is accumulated in a predetermined place in the reducing agent path from the outlet portion of the reducing agent tank to the reducing agent addition means, and the pump is started next time. Sometimes, provided with a feeding structure that enables feeding of the reducing agent from the reducing agent tank to the reducing agent addition means even when the residual reducing agent is in a frozen state ,
As the feeding structure, an upper piping portion and a lower piping portion provided by branching a part of the reducing agent pipe from the outlet portion of the reducing agent tank to the reducing agent addition means into two upper and lower systems,
The lower piping part is a reducing agent reservoir part that is provided at the lowest position in the middle of the reducing agent path from the outlet part of the reducing agent tank to the reducing agent addition means, and accumulates the residual reducing agent,
The upper pipe portion is an empty space after the reducing agent discharge process is performed, and is a route communication portion that connects the reducing agent path on the reducing agent tank side and the reducing agent path on the reducing agent addition means side more than that. A reducing agent supply system characterized by being. The reducing agent supply system according to claim 5 , wherein the lower piping section has a larger opening cross section than the upper piping section. The reducing agent supply system according to any one of claims 1 to 6 , wherein the reducing agent reservoir has a volume larger than a predicted residual amount of the reducing agent after the reducing agent discharge process. Applied to an exhaust gas purification apparatus provided with an NOx catalyst provided in an exhaust passage of an internal combustion engine and purifying NOx in exhaust gas by the reducing agent;
The reducing agent supply system according to any one of claims 1 to 7 , wherein the NOx catalyst is the reduction reaction device, and the reducing agent is added to the upstream side of the NOx catalyst in the exhaust passage.

Images