JP5062780B2 - Exhaust purification system and control method of exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust purification system and an exhaust purification system control method. In particular, the present invention relates to an exhaust purification system and an exhaust purification system control method that can eliminate clogging of a reducing agent injection valve caused by solidification of an aqueous urea solution.

Conventionally, exhaust gas of an internal combustion engine mounted on a vehicle contains nitrogen oxide (hereinafter referred to as “NO _X ”) and particulate matter (hereinafter referred to as “PM”).
Among them, there is a urea SCR system as a device for purifying exhaust gas by reducing NO _X. The urea SCR system is a kind of a reducing agent supply device for supplying a urea aqueous solution as a reducing agent pumped up from a storage tank by a pressure pump into an exhaust pipe and an exhaust purification catalyst capable of adsorbing ammonia. And a certain SCR catalyst. In such a urea SCR system, ammonia generated by decomposition of an aqueous urea solution is adsorbed on the SCR catalyst, and NO _x in the exhaust gas is reacted with ammonia in the SCR catalyst to purify the exhaust gas.

On the other hand, there is a diesel particulate filter (hereinafter referred to as “DPF”) as an apparatus for collecting PM and purifying exhaust gas. The DPF is disposed in the exhaust pipe of the internal combustion engine, and collects PM in the exhaust gas when the exhaust gas passes through the DPF. In an exhaust purification system equipped with a DPF, in order to prevent clogging of the DPF, forced regeneration control for forcibly burning the PM deposited on the DPF by raising the temperature of the DPF to about 500 ° C. to 600 ° C. in a timely manner. Done.
In recent years, exhaust gas purification systems equipped with both a DPF and an SCR catalyst have increased with the increase in exhaust gas purification standards.

By the way, the urea SCR system is generally configured to recover the urea aqueous solution remaining in the reducing agent supply path when the internal combustion engine is stopped (see, for example, Patent Document 1). As a result, it is possible to prevent the urea aqueous solution from being frozen while being present in the reducing agent supply path and clogging in the reducing agent supply path.

JP 2009-215891 A

  However, in the exhaust gas purification system described in Patent Document 1, the urea aqueous solution in the reducing agent injection valve is warmed after the internal combustion engine is stopped, and then the urea aqueous solution is solidified in the course of cooling, resulting in the internal combustion engine. At the time of starting, there is a problem that the supply of the urea aqueous solution is hindered and the exhaust purification efficiency is lowered.

More specifically, in the exhaust purification system, when the internal combustion engine is stopped, a purging process for collecting the urea aqueous solution filled in the reducing agent supply device into the storage tank is generally performed, but the storage tank and the reducing agent injection valve are provided. Due to the structure of the reducing agent passage to be connected, the urea aqueous solution filled in the reducing agent supply device may not be completely recovered in the storage tank.
On the other hand, as the internal combustion engine is stopped, the circulation of the cooling water, which is the heat radiation function of the reducing agent injection valve, is stopped, so the temperature of the reducing agent injection valve rises. If it does so, the water | moisture content in the urea aqueous solution which remained in the above-mentioned reducing agent injection valve will escape by vaporization, and the density | concentration will rise. After that, the temperature of the urea aqueous solution decreases as the temperature of the exhaust pipe and the surroundings decreases. However, since the concentration is higher than the normal concentration, the temperature of solidification also rises, and the residual urea aqueous solution solidifies, causing the reducing agent injection. There is a risk of clogging of the valve.
The concentration of the aqueous urea solution is usually adjusted to about 32.5%. In this case, the temperature at which the aqueous urea solution solidifies is about -11 ° C. When the concentration exceeds the percentage, the temperature at which the urea aqueous solution solidifies tends to increase. Therefore, the residual urea aqueous solution in the reducing agent injector whose concentration has been increased due to the loss of moisture due to the high temperature is likely to solidify when the temperature decreases, and the reducing agent injector does not react when the internal combustion engine is restarted. Injection may be hindered.

Therefore, in view of such a problem, the inventor of the present invention determines whether or not the urea aqueous solution once warmed may be solidified in the cooling process after the internal combustion engine is stopped. Has found that such a problem can be solved by prohibiting the stop of the internal combustion engine, and has completed the present invention.
That is, the present invention provides an exhaust purification system and a control method for the exhaust purification system that can prevent clogging of the reducing agent injection valve due to solidification of the urea aqueous solution, and thus prevent a reduction in exhaust purification efficiency. The purpose is to do.

According to the present invention, a DPF that collects exhaust particulates in exhaust gas that is exhausted, a reducing agent injection valve that injects urea aqueous solution as a reducing agent into the exhaust gas, In an exhaust gas purification system, an SCR catalyst for purifying NO _x is sequentially provided from the exhaust upstream side, and a cooling water passage through which the cooling water of the internal combustion engine can flow is provided in the housing of the reducing agent injection valve . When it is determined that the urea aqueous solution may solidify when it is detected that the ignition switch is turned off during operation, and when it is determined that the urea aqueous solution may solidify, An exhaust gas purification system including an internal combustion engine stop prohibiting unit that prohibits stop of the internal combustion engine is provided, and the above-described problems can be solved.

In this way, it is determined whether there is a possibility that the urea aqueous solution in the reducing agent injection valve may solidify and prohibits the stop of the internal combustion engine. It is possible to prevent clogging of the reducing agent injection valve due to this, and consequently to prevent a reduction in exhaust purification efficiency.

Further, in configuring the present invention, the condition establishment determination unit detects that the ignition switch has been turned off until the DPF forced regeneration is completed after the start or within a predetermined period after the completion. It is preferable to determine that the urea aqueous solution may be solidified.
In this way, during the forced regeneration of the DPF and for a predetermined period after the completion, the reducing agent injection valve downstream of the DPF is exposed to a high temperature, and after the internal combustion engine is stopped, its cooling function does not work effectively, Since the concentration of the urea aqueous solution remaining in the agent injection valve increases, it can be determined that the possibility of solidification is high.

Further, in configuring the present invention, when the condition establishment determination unit detects that the ignition switch is turned off, the condition establishment determination unit determines whether the urea is based on at least one of the temperature of the reducing agent injection valve, the temperature gradient, and the outside air temperature. It is preferable to determine whether or not the aqueous solution may solidify.
Whether or not the urea aqueous solution in the reducing agent injection valve is solidified depends on the temperature of the reducing agent injection valve. Therefore, by determining based on the temperature of the reducing agent injection valve, the temperature gradient, and the outside air temperature, The risk of solidification can be grasped more accurately.

In another aspect of the present invention, a DPF that collects exhaust particulates in exhaust gas, a reducing agent injection valve that injects a urea aqueous solution as a reducing agent into the exhaust gas, and a urea aqueous solution in the exhaust gas. comprising a SCR catalyst for purifying NO _X in the sequentially from the exhaust upstream side, in the control method of the reducing agent exhaust gas purification system coolant passage cooling water can flow in the housing to the internal combustion engine of the injection valve is provided When it is detected that the ignition switch is turned off during the operation of the internal combustion engine, the step of determining whether or not the urea aqueous solution may be solidified, and the case of determining that the urea aqueous solution may be solidified And a step of prohibiting the stop of the internal combustion engine.
In this way, it is determined whether there is a possibility that the urea aqueous solution in the reducing agent injection valve may solidify and prohibits the stop of the internal combustion engine. It is possible to prevent clogging of the reducing agent injection valve due to this, and consequently to prevent a reduction in exhaust purification efficiency.

1 is an overall view showing a configuration example of an exhaust purification system according to an embodiment of the present invention. It is a block diagram which shows the structural example of the control apparatus with which an exhaust gas purification system is equipped. It is a timing chart for demonstrating the control method of an exhaust gas purification system. It is a flowchart for demonstrating the control method of an exhaust gas purification system. It is a flowchart for demonstrating the control method of an exhaust gas purification system. It is a flowchart for demonstrating the control method of an exhaust gas purification system. It is a timing chart for demonstrating the control method of an exhaust gas purification system. 4 is a graph showing the relationship between the concentration of an aqueous urea solution and the solidification temperature T0.

DESCRIPTION OF EMBODIMENTS Embodiments relating to an exhaust purification system and an exhaust purification system control method according to the present invention will be specifically described below with reference to the drawings.
However, the following embodiment shows one aspect of the present invention and does not limit the present invention, and can be arbitrarily changed within the scope of the present invention.
In addition, what is attached | subjected with the same code | symbol in each figure has shown the same member thru | or part, and abbreviate | omitting description suitably.

1. Exhaust Purification System (1) Overall Configuration FIG. 1 shows an overall configuration of an exhaust purification system (hereinafter sometimes simply referred to as “system”) 10 according to the present embodiment.
The system 10 includes an exhaust purification unit 20 having a DPF 22 and an SCR catalyst 24, a reducing agent supply device 40 including a reducing agent injection valve 43, and a control device that performs forced regeneration control of the DPF 22 and operation control of the reducing agent supply device 40. 60 as the main elements.
Such a system 10 is configured as an apparatus for collecting PM in exhaust gas by the DPF 22 and selectively purifying NO _X in the exhaust gas in the SCR catalyst 24 using urea aqueous solution as a reducing agent. It has been done.

(2) Exhaust purification unit The exhaust purification unit 20 includes an oxidation catalyst 21, a DPF 22, and an SCR catalyst 24 sequentially from the exhaust upstream side.

  Among the constituent elements of the exhaust purification unit 20, the oxidation catalyst 21 oxidizes unburned fuel supplied into the exhaust pipe 11 by post injection or the like in the internal combustion engine 5 to generate oxidation heat. Thereby, the temperature of the exhaust gas flowing into the DPF 22 can be raised to heat the DPF 22. The oxidation catalyst 21 may be a known catalyst, for example, a catalyst in which platinum is supported on alumina and a predetermined amount of rare earth element such as cerium is added.

  Further, the DPF 22 collects PM in the exhaust gas when the exhaust gas passes through the DPF 22. In the system 10 shown in FIG. 1, the DPF 22 is disposed on the exhaust upstream side of the SCR catalyst 24, and there is no possibility that PM adheres to the SCR catalyst 24. As the DPF 22, a known filter, for example, a honeycomb structured filter made of a ceramic material can be used.

The SCR catalyst 24 adsorbs ammonia generated by the decomposition of the urea aqueous solution injected into the exhaust gas by the reducing agent injection valve 43, and reduces NO _x in the inflowing exhaust gas. As the SCR catalyst 24, for example, a zeolite-based reduction catalyst having an ammonia adsorption function and capable of selectively reducing NO _x can be used.

The exhaust purification unit 20 described above includes pressure sensors 51 and 52 before and after the DPF 22, and includes temperature sensors 53 and 54 before and after the SCR catalyst 24, respectively. Further, an NO _X sensor 55 is provided on the exhaust downstream side of the SCR catalyst 24. Further, an outside air temperature sensor for detecting the outside air temperature is disposed around the exhaust purification unit.
Sensor values of these sensors are sent to the controller 60, the pressure and temperature at each position, NO _X concentration is detected.
Note that these sensors can be omitted if they can be estimated by calculation.

The exhaust purification unit 20 described above includes a connecting pipe 12 that branches from the first bent portion 23 a of the exhaust pipe 11 and fixes the reducing agent injection valve 43. The urea aqueous solution is injected from the reducing agent injection valve 43 through the connection pipe 12 in a direction substantially coinciding with the flow direction of the exhaust gas.
Therefore, compared with the case where the reducing agent injection valve 43 is directly fixed to the exhaust pipe 11, it is possible to make it difficult to transfer heat from the exhaust pipe 11 or the exhaust gas to the reducing agent injection valve 43.

(3) Forced Regeneration Unit Here, the system 10 of the present embodiment includes a forced regeneration unit for performing forced regeneration control of the DPF 22. This is because the DPF 22 is heated to about 500 ° C. to 600 ° C. and the PM deposited on the DPF 22 is forcibly burned.
In the present embodiment, a fuel injection valve (not shown) that supplies unburned fuel into the exhaust pipe 11 by post-injection or the like in the internal combustion engine 5, fuel injection amount from the fuel injection valve, fuel injection timing, etc. The control part of the control device 60 for instructing the control of the valve and the oxidation catalyst 21 that oxidizes unburned fuel and generates heat of oxidation constitute a forced regeneration means.

  The forced regeneration means is not limited to the above example, and any means that can raise the temperature of the exhaust gas to about 500 ° C. to 600 ° C. may be used. For example, the forced regeneration means may be configured using an apparatus that supplies unburned fuel to the oxidation catalyst 21 without relying on post injection. Further, a heating device such as a burner or a heating wire may be provided to heat the DPF 22 directly.

(4) Reducing agent supply device Moreover, the reducing agent supply device 40 is provided with the storage tank 41 which stores urea aqueous solution, the pressure feed pump 42, and the reducing agent injection valve 43 as main elements.
Among these, the storage tank 41 and the pressure feed pump 42 are connected by a first supply passage 44, and the pressure feed pump 42 and the reducing agent injection valve 43 are connected by a second supply passage 45. A pressure sensor 56 is provided in the second supply passage 45, the sensor value is transmitted to the control device 60, and the pressure in the second supply passage 45 is detected.
In addition, the second supply passage 45 and the storage tank 41 are connected by the third supply passage 46, whereby the excess urea aqueous solution supplied to the second supply passage 45 is returned to the storage tank 41. Can do.

The reducing agent supply device 40 has a function of switching the flow path of the urea aqueous solution from the forward direction from the storage tank 41 to the reducing agent injection valve 43 to the reverse direction from the reducing agent injection valve 43 to the storage tank 41. A reverting valve 47 is provided.
That is, the system 10 of the present embodiment is configured such that the urea aqueous solution filled in the reducing agent supply device 40 can be collected in the storage tank 41 when the internal combustion engine 5 is stopped.

  Among the constituent elements of the reducing agent supply device 40, the pumping pump 42 pumps up the urea aqueous solution in the storage tank 41 so that the pressure in the second supply path 45 is maintained at a predetermined value, and the reducing agent injection valve. 43 is pumped. As the pressure pump 42, an electric pump is typically used.

  Further, the reducing agent injection valve 43 injects an aqueous urea solution into the exhaust pipe 11 when the reducing agent injection valve 43 is opened by a control signal output from the control device 60. As the reducing agent injection valve 43, for example, an ON-OFF valve whose ON / OFF is controlled by DUTY control is used.

The electronic part, the resin part, and the like constituting the reducing agent injection valve 43 are relatively weak against heat, and the heat-resistant temperature Tlim is about 140 ° C. to 150 ° C., while the exhaust gas temperature during normal operation is 200 ° C. It is about -300 degreeC.
Therefore, the reducing agent supply device 40 includes a cooling water passage 35 provided in the housing of the reducing agent injection valve 43 and a cooling water circulation passage 33 that branches from the cooling water passage 33 of the internal combustion engine 5 and communicates with the cooling water passage 35. 34, and cooling water flow rate control valves 31 and 32 for adjusting the flow rate of the cooling water flowing through the cooling water circulation passages 33 and 34 are provided.
Thereby, the cooling water of the internal combustion engine 5 is circulated through the cooling water passage 35 of the reducing agent injection valve 43, the temperature of the reducing agent injection valve 43 is maintained at about 70 ° C to 80 ° C, and the reducing agent injection valve 43 is thermally damaged. Can be prevented.
Further, since the urea aqueous solution having a relatively low temperature in the storage tank 41 is pumped to the reducing agent injection valve 43 as the reducing agent is injected from the reducing agent injection valve 43, The heat transfer also promotes heat dissipation of the reducing agent injection valve 43.

Such a heat dissipation capability of the reducing agent injection valve 43 due to the circulation of the engine cooling water and the heat transfer to the urea aqueous solution is exhibited particularly during the operation of the internal combustion engine 5.
This is because the engine coolant circulates during the operation of No. 5 and the urea aqueous solution is pumped to the reducing agent injection valve 43 during the operation of the internal combustion engine 5.

2. Control Device (1) Overall Configuration Next, referring to FIG. 2, the control device 60 provided in the system 10 of the present embodiment includes a temperature detection unit 62, a forced regeneration control unit 63, and a condition establishment determination unit 64. The internal combustion engine stop prohibiting unit 65 will be described in detail. Specifically, each of these units is realized by executing a program by a microcomputer.
That is, FIG. 2 is a configuration in which a portion related to control for eliminating clogging of the reducing agent injection valve 43 due to solidification of the urea aqueous solution in the control device 60 provided in the system 10 is represented by a functional block. It is an example.

  The control device 60 includes a signal from the ignition switch 57, each pressure sensor and each temperature sensor, a rotational speed sensor for detecting the engine rotational speed Ne, a vehicle speed sensor for detecting the vehicle speed V of the vehicle, and an accelerator pedal operation amount Acc. Various sensor signals such as an accelerator sensor for detecting the brake and a brake sensor for detecting an operation amount Brk of the brake pedal can be read. Further, the control device 60 is provided with a RAM (Random Access Memory) (not shown) for storing calculation results and detection results at each unit. Furthermore, the control device 60 is configured to make a determination when an off signal is detected from the ignition switch 57, and depending on the determination result, the operation of the internal combustion engine can be continued.

During the operation of the internal combustion engine 5, the control device 60 controls the driving of the pumping pump 42 so that the pressure in the second supply path 45 is maintained at a predetermined value, and the engine speed Ne. Further, the driving of the reducing agent injection valve 43 is controlled based on the sensor value of the NO _X sensor 55 provided on the exhaust downstream side of the SCR catalyst.
In addition, the control device 60 performs a purge process when the internal combustion engine 5 is stopped. Specifically, a signal for switching the flow path of the urea aqueous solution from the forward direction to the reverse direction is output to the reverting valve 47, and the reducing agent injection valve 43 is opened to drive the pressure feed pump 42. Is output to the pressure feed pump 42 and the reducing agent injection valve 43.

(2) Temperature detection unit The temperature detection unit 62 is for detecting the reducing agent injection valve temperature Tudv. If it cannot be directly detected, the temperature detection unit 62 obtains the temperature from the DPF 22 downstream temperature Tdpf in the vicinity thereof. Also good.

(3) Forced regeneration control unit The forced regeneration control unit 63 estimates the PM deposition amount Vpm based on the differential pressure obtained from the pressure sensors 51 and 52 provided before and after the DPF 22. When the estimated PM accumulation amount Vpm exceeds a predetermined threshold value Vpm0, it is determined that the forced regeneration of the DPF 22 is necessary, and a signal for executing the forced regeneration is transmitted to the forced regeneration means.
On the other hand, the forced regeneration control unit 63 stops the signal for executing the forced regeneration, which has been transmitted to the forced regeneration means, triggered by the estimated PM accumulation amount Vpm being reduced to a predetermined amount.

(4) Condition Satisfaction Determining Unit The condition satisfaction determining unit 64 determines whether or not the urea aqueous solution in the reducing agent injection valve 43 may be solidified when detecting that the ignition switch 57 is turned off.
When the internal combustion engine 5 is stopped after the ignition switch 57 is turned off, the circulation of the cooling water in the internal combustion engine 5 is also stopped, so that the heat dissipating ability of the reducing agent injection valve 43 is not effectively exhibited. The temperature of the urea aqueous solution rises, and the vaporization of the water therein becomes intense. Then, the concentration of the urea aqueous solution increases, and accordingly, the solidification temperature T0 of the urea aqueous solution also increases. Therefore, when it is estimated that the temperature of the urea aqueous solution is lower than the solidification temperature T0 during the cooling process after the internal combustion engine 5 is stopped, it is determined that the urea aqueous solution is solidified.

As a more specific determination condition, it can be determined that the urea aqueous solution may be solidified when it is detected that the ignition switch 57 is turned off during the forced regeneration of the DPF or within a predetermined period after the forced regeneration. .
That is, immediately after the forced regeneration heat of the DPF or immediately after the regeneration, the exhaust downstream side of the DPF 22 is heated to a very high temperature, and the temperature of the reducing agent injection valve tends to be high, and the concentration of the urea aqueous solution that causes solidification This is because it can be determined that an increase is likely to occur.
Here, the predetermined period is a period in which the influence of high heat due to the residual heat after the forced regeneration reaches the reducing agent injection valve 43, and varies depending on the distance from the DPF 22 to the reducing agent injection valve 43, the heat capacity of the exhaust pipe, etc. It is desirable to make a determination based on the results of the test. That is, after the forced regeneration is finished on the actual machine, the test is performed while changing the time until the internal combustion engine 5 is stopped, and in each case, it is confirmed whether the urea aqueous solution in the reducing agent injection valve 43 is solidified. A predetermined time can be determined.

As another determination condition, when it is detected that the ignition switch 57 is turned off, the urea aqueous solution may solidify based on the reducing agent injection valve temperature Tudv, the temperature gradient δTudv, and the outside air temperature Tout. It is determined whether or not.
This is because when the reducing agent injection valve temperature Tudv is high, the vaporization of moisture in the aqueous urea solution proceeds, the concentration increases, and the solidification temperature T0 rises, and the possibility that the aqueous urea solution solidifies after cooling increases. Further, when the temperature gradient ΔTudv of the reducing agent injection valve is large or when the outside air temperature Tout is high, the possibility that the aqueous urea solution is solidified similarly becomes high. Based on these, or these and the reducing agent injection valve It can be determined by appropriately combining the temperature Tudv.
Here, the reducing agent injection valve temperature Tudv used for the determination may be a temperature at that time, or may be a temperature estimated to be reached thereafter. Moreover, it is good also as reducing agent injection valve ultimate temperature Tudvmax as shown in FIG. 3, FIG.
A test is performed on an actual machine, and a specific determination is made based on whether the urea aqueous solution in the reducing agent injection valve 43 is solidified by changing the conditions of the reducing agent injection valve temperature Tudv, the temperature gradient δTudv, and the outside air temperature Tout in various ways. It is good to decide the standard. Incidentally, when the reducing agent injection valve temperature Tudv exceeds about 100 ° C., there is a high possibility that the urea aqueous solution is solidified in the subsequent cooling process.

(5) Internal combustion engine stop prohibition unit The internal combustion engine stop prohibition unit 65 prohibits the stop of the internal combustion engine when it is determined that the urea aqueous solution may be solidified when the internal combustion engine is stopped.
When it is determined that the ignition switch 57 is turned off during the operation of the internal combustion engine and the internal combustion engine is stopped, it is determined that the urea aqueous solution may solidify in the cooling process after the stop. Prohibits stopping the internal combustion engine. Further, the prohibition is continued until the risk of solidification disappears, and after the risk of solidification disappears, the internal combustion engine is allowed to stop.

3. Control Method A specific example of a control method that can be executed by the present control apparatus will be described below using a timing chart and a flowchart.

FIGS. 3 and 7 are timing charts for explaining a case where the ignition switch 57 is turned off during the forced regeneration of the DPF 22. The DPF downstream exhaust temperature Tdpf, the reducing agent injection valve temperature Tudv, the reducing agent injection valve 43 are illustrated in FIGS. Changes in the solidification temperature T0 of the aqueous urea solution are shown.
4, 5, and 6 show flowcharts of arithmetic processing in the control device 60 when it is detected that the ignition switch 57 is turned off.

First, when the forced regeneration of the DPF 22 starts at t1 in FIG. 3, the DPF downstream exhaust temperature Tdpf rises due to the regeneration heat due to the forced regeneration. The DPF downstream exhaust temperature Tdpf in a situation where forced regeneration is not performed is normally about 200 to 300 ° C., but when forced regeneration is started, the DPF downstream exhaust temperature Tdpf reaches about 500 to 600 ° C. .
Along with this, the reducing agent injection valve temperature Tudv also rises. However, when the internal combustion engine 5 is in operation, the engine cooling water circulates in the cooling water passage 35 of the housing of the reducing agent injection valve 43, and in the storage tank 41. Since the urea aqueous solution having a relatively low temperature is pumped to the reducing agent injection valve 43, the reducing agent injection valve temperature Tudv does not exceed a certain temperature, and a new urea aqueous solution is also supplied. The change in the solidification temperature T0 of the urea aqueous solution in the reducing agent injection valve 43 is small.

In step S1 of FIG. 4, when the control device 60 detects that the ignition switch 57 is turned off, the process proceeds to step S2 to determine whether or not the solidification condition is satisfied. That is, when it is assumed that the internal combustion engine 5 is stopped by turning off the ignition switch 57, it is determined whether or not the urea aqueous solution may be solidified in the cooling process after the stop.
A specific example of the determination method will be described later with reference to FIGS.
If it is determined that there is a risk, the process proceeds to step S3, the stop of the internal combustion engine is prohibited, and the process returns to step S2. When it is determined that there is no fear, the process proceeds to step S4, the stop of the internal combustion engine is permitted, and this routine is terminated. Therefore, the stop of the internal combustion engine 5 is prohibited until the risk of solidification disappears, and the stop of the internal combustion engine 5 is permitted after the risk of solidification disappears.

Returning to FIG. 3, the determination method for the establishment of the solidification condition will be described in detail. Assuming that the internal combustion engine 5 is stopped at the time t2 when it is detected that the ignition switch 57 is turned off, the estimation of each subsequent temperature change at that time is shown by a one-dot chain line in FIG. While the DPF 22 exhaust downstream temperature Tdpf gradually decreases, the circulation of the cooling water in the internal combustion engine 5 is stopped, so that the heat radiation capability of the reducing agent injection valve 43 is not effectively exhibited. Then, since the DPF 22 exhaust downstream temperature Tdpf is high after the time t2, the reducing agent injection valve temperature Tudv rises and no new urea aqueous solution is supplied, so the concentration of the urea aqueous solution in the reducing agent injection valve 43 is increased. It is estimated that the solidification temperature T0 of the urea aqueous solution also rises.
In the course of cooling, when it is estimated that the reducing agent injection valve temperature Tudv is lower than the increased solidification temperature T0, it is determined that the urea aqueous solution in the reducing agent injection valve 43 may be solidified. In FIG. 3, it is estimated that at time t3, the reducing agent injection valve temperature Tudv is lower than the solidification temperature T0, and the urea aqueous solution in the reducing agent injection valve 43 starts to solidify. Therefore, in this case, it is determined that the urea aqueous solution in the reducing agent injection valve 43 may be solidified, and the stop of the internal combustion engine 5 is prohibited (step S3 in FIG. 4).

On the other hand, FIG. 7 shows a case where after the ignition switch 57 is detected to be off, the internal combustion engine 5 is prohibited from being stopped and the operation of the internal combustion engine is continued. 7 indicates an estimation result of the reducing agent injection valve temperature Tudv and the like when it is assumed that the internal combustion engine 5 has been stopped at the time t2 ′. Based on this, it is estimated that the reducing agent injection valve temperature Tudv does not fall below the solidification temperature T0 of the urea aqueous solution. Therefore, even if the internal combustion engine 5 is stopped, there is no possibility of solidification of the urea aqueous solution, so that the internal combustion engine 5 is allowed to stop (step S4 in FIG. 4).

FIG. 5 shows a flowchart including one of the concrete solidification condition establishment determination methods with respect to FIG.
In step S21, when the control device 60 detects that the ignition switch 57 is turned off, the process proceeds to step S22, and it is determined whether or not the DPF 22 is being forcedly regenerated or within a predetermined period after forced regeneration. When the DPF 22 is being forcibly regenerated or during a predetermined period after the forced regeneration, the process proceeds to step S23, the stop of the internal combustion engine is prohibited, and the process returns to step S22. If the DPF 22 is neither forcibly regenerated nor for a predetermined period after forced regeneration, the process proceeds to step S24, where the internal combustion engine is allowed to stop, and this routine is terminated. Therefore, the stop of the internal combustion engine 5 is prohibited until a predetermined period after the forced regeneration of the DPF 22 passes, and the stop of the internal combustion engine 5 is permitted after the predetermined period has elapsed.

Further, FIG. 6 shows a flowchart including one of the specific solidification condition establishment determination methods different from FIG.
In step S31, when the control device 60 detects that the ignition switch 57 is turned off, the process proceeds to step S32, and it is determined whether or not the reducing agent injection valve temperature Tudv is higher than the threshold value Ts. When the reducing agent injection valve temperature Tudv is equal to or higher than the threshold value Ts, the process proceeds to step S33, the stop of the internal combustion engine is permitted, and this routine is ended. When the reducing agent injection valve temperature Tudv is lower than the threshold value Ts, the routine proceeds to step S24, the stop of the internal combustion engine 5 is permitted, and this routine is ended. Therefore, the stop of the internal combustion engine 5 is prohibited until the reducing agent injection valve temperature Tudv becomes lower than the threshold value Ts, and the internal combustion engine 5 is allowed to stop after the reducing agent injection valve temperature Tudv becomes lower than the threshold value Ts.
Here, the reducing agent injection valve temperature Tudv may be a temperature at that time, or a temperature estimated to be reached thereafter. Moreover, it is good also as reducing agent injection valve ultimate temperature Tudvmax as shown in FIG. 3, FIG.
The threshold value Ts is approximately 100 ° C.

  According to the exhaust purification system and the exhaust purification system control method of the present embodiment, when it is detected that the ignition switch 57 is turned off, the internal combustion engine 5 is stopped and then the reducing agent injection valve 43 is cooled during the cooling process. It is possible to prevent the urea aqueous solution from solidifying by determining whether or not there is a risk of solidification of the remaining urea aqueous solution and prohibiting the stop of the internal combustion engine 5 while there is a possibility of solidification. Therefore, it is possible to prevent the exhaust purification efficiency from being lowered due to the solidification of the urea aqueous solution.

5: Internal combustion engine, 10: Exhaust purification system (system), 11: Exhaust pipe, 12: Connection pipe, 20: Exhaust purification unit, 20a and 20b: Flange, 21: Oxidation catalyst, 22: Diesel particulate filter (DPF) ), 23a / 23b: bent portion, 24: SCR catalyst, 31/32: cooling water circulation valve, 33/34: cooling water circulation passage, 40: reducing agent supply device, 41: storage tank, 42: pressure pump, 43: reduction Agent injection valve, 44: first supply passage, 45: second supply passage, 46: third supply passage, 51/52: pressure sensor, 53/54: temperature sensor, 55: NO _X sensor, 56: Pressure sensor, 57: Ignition switch, 60: Control device, 62: Temperature detection unit, 63: Forced regeneration control unit, 64: Condition establishment determination unit, 65: Internal combustion engine stop prohibition unit

Claims (4)

A DPF that collects exhaust particulates in exhaust gas, a reducing agent injection valve that injects urea aqueous solution as a reducing agent into the exhaust gas, and an SCR that purifies NO _x in the exhaust gas using the urea aqueous solution An exhaust purification system comprising a catalyst, and a cooling water passage through which the cooling water of the internal combustion engine can be circulated in a housing of the reducing agent injection valve .
A condition establishment determination unit that determines whether the urea aqueous solution may solidify when it is detected that the ignition switch is turned off during operation of the internal combustion engine;
An internal combustion engine stop prohibiting unit that prohibits the stop of the internal combustion engine when it is determined that the urea aqueous solution may solidify;
An exhaust purification system comprising:   The condition establishment determining unit solidifies the urea aqueous solution when it is detected that the ignition switch is turned off until the DPF forced regeneration is completed after the start or within a predetermined period after the completion. The exhaust purification system according to claim 1, wherein it is determined that there is a risk.   When the condition establishment determination unit detects that the ignition switch is turned off, the urea aqueous solution may solidify based on at least one of the temperature of the reducing agent injection valve, the temperature gradient, and the outside air temperature. The exhaust purification system according to claim 1, wherein it is determined whether or not there is an exhaust gas. A DPF that collects exhaust particulates in exhaust gas; a reducing agent injection valve that injects urea aqueous solution as a reducing agent into the exhaust gas; and an SCR catalyst that purifies NOx in the exhaust gas using the urea aqueous solution. In order from the exhaust upstream side, and a control method of the exhaust purification system in which a cooling water passage through which the cooling water of the internal combustion engine can flow is provided in the housing of the reducing agent injection valve ,
When the ignition switch during operation of the internal combustion engine is detected to be turned off, and determining whether a possibility exists that the aqueous urea solution is solidified,
A step of prohibiting the stop of the internal combustion engine when it is determined that the urea aqueous solution may solidify;
A control method for an exhaust purification system, comprising:

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