JPWO2014171261A1 - Exhaust purification system and control method of exhaust purification system - Google Patents

Abstract

Provided are an exhaust purification system and a control method therefor that can prevent occurrence of clogging or breakage of a reducing agent injection valve due to solidification of the reducing agent and prevent a reduction in exhaust purification efficiency. An exhaust purification system and a control method thereof according to an aspect of the present invention specify a maximum reached temperature of a reducing agent injection valve after detecting that an ignition switch is turned off, and then dissolve a urea aqueous solution remaining in the reducing agent injection valve. A configuration is provided in which the temperature is calculated based on the maximum attained temperature, and the operation of the reducing agent injection valve is permitted after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after the ignition switch is turned on.

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 capable of avoiding clogging or breakage of a reducing agent injection valve and a reducing agent supply path due to solidification of an aqueous urea solution.

  Conventionally, exhaust gas of an internal combustion engine mounted on a vehicle includes nitrogen oxides (hereinafter referred to as “NOx”) and particulate matter (hereinafter also referred to as “PM”). Yes. Among these, there is a urea SCR system as a device for purifying exhaust gas by reducing NOx. 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 NOx 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 is performed in a timely manner in which the temperature of the DPF is raised to about 500 ° C. to 600 ° C. and the PM deposited on the DPF is forcibly burned. 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.

  The urea SCR system is usually 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, the urea aqueous solution is frozen while remaining in the reducing agent supply path, and it is intended to avoid clogging or breakage of the reducing agent supply path.

JP 2008-101564 A

  However, in the reducing agent supply apparatus, it is usual that the reducing agent, that is, the urea aqueous solution cannot be completely recovered due to its structure.

  Therefore, the urea aqueous solution remaining in the reducing agent supply path, particularly the reducing agent injection valve, is heated and concentrated after the internal combustion engine is stopped, so that the solidification temperature rises and the urea aqueous solution is solidified in the process of cooling thereafter. As a result, for example, the exhaust purification system described in Patent Document 1 has a problem in that the supply of urea aqueous solution is hindered when the internal combustion engine is started, and the exhaust purification efficiency decreases.

More specifically, in the exhaust purification system, when the internal combustion engine is stopped, a purge process is generally performed in which the urea aqueous solution filled in the reducing agent supply path of the reducing agent supply device is collected in the storage tank. Due to the structure of the reducing agent passage connecting the reducing agent injection valve or the like, the urea aqueous solution filled in the reducing agent supply path cannot normally be completely recovered in the storage tank.

  On the other hand, with the stop of the internal combustion engine, the circulation of the cooling water, which is the heat radiation function of the reducing agent injection valve, is stopped, so that the temperature of the reducing agent injection valve increases. If it does so, the water | moisture content in the urea aqueous solution which remained in the above-mentioned reducing agent injection valve will evaporate by vaporization, and the density | concentration will rise. Thereafter, as the temperature of the exhaust pipe and the surroundings decreases, the temperature of the urea aqueous solution decreases. However, since the concentration is higher than the normal concentration, the temperature for solidification increases, and the residual urea aqueous solution solidifies. This may cause clogging of the reducing agent injection valve.

  FIG. 8 is a graph showing the relationship between the concentration of the urea aqueous solution and the solidification temperature T0.

  The concentration of the urea aqueous solution as the reducing agent used in the reducing agent supply apparatus is usually adjusted to about 32.5%, which is about −11 ° C., which has the lowest solidification temperature.

  As shown in the graph of FIG. 8, the solidification temperature of the urea aqueous solution is about −11 ° C., which is the lowest when the concentration of the urea aqueous solution is about 32.5%, and the concentration of the urea aqueous solution is about 32.5%. The solidification temperature of the urea aqueous solution has a characteristic that it rises regardless of whether it becomes higher or lower.

  Therefore, the remaining urea aqueous solution in the reducing agent injector whose concentration has increased due to evaporation of moisture due to high temperature is likely to solidify when the temperature subsequently decreases, and injection of the reducing agent injector is performed when the internal combustion engine is restarted. In the worst case, the reducing agent injection valve may be damaged.

  The present invention has been made in view of such a problem. Even when the urea aqueous solution once heated is solidified in the cooling process after the internal combustion engine is stopped, the solidified urea aqueous solution is dissolved. The above-mentioned problem is solved by operating the reducing agent supply device after waiting.

  That is, the present invention can avoid the occurrence of clogging or breakage of the reducing agent injection valve or the reducing agent supply path due to the solidification of the urea aqueous solution, and as a result, the exhaust purification efficiency can be prevented from lowering. An object of the present invention is to provide an exhaust purification system and an exhaust purification system control method.

An exhaust purification system according to an aspect of the present invention includes a diesel particulate filter that collects exhaust particulates in exhaust gas of an internal combustion engine, and a urea aqueous solution as a reducing agent supplied from a storage tank to a reducing agent injection valve. When the internal combustion engine is stopped by being injected into the exhaust gas and supplied, the reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank, and the urea aqueous solution is used to supply the urea aqueous solution to the storage tank. An exhaust gas purification system comprising an SCR catalyst for purifying NOx of the exhaust gas sequentially from the exhaust upstream side,
After detecting that the ignition switch for stopping the internal combustion engine is turned off, the maximum reached temperature of the reducing agent injection valve is identified, and then the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve is reached. A melting temperature calculation part for calculating based on the temperature;
An injection valve operation permission unit for permitting the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detection of turning on of an ignition switch for starting the internal combustion engine; ,
It is characterized by providing the control apparatus which has, and the said subject can be solved by providing the said structure.

Further, an exhaust purification system control method according to an aspect of the present invention includes:
A diesel particulate filter that collects exhaust particulates in the exhaust gas of an internal combustion engine and a urea aqueous solution as a reducing agent are supplied from the storage tank to the reducing agent injection valve by being injected and supplied into the exhaust gas. When the internal combustion engine is stopped, a reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank and an SCR catalyst that purifies NOx in the exhaust gas using the urea aqueous solution are exhausted upstream. In the exhaust purification system control method provided sequentially from the side,
A process of identifying the highest temperature reached by the reducing agent injection valve after detecting the ignition switch OFF for stopping the internal combustion engine;
Calculating the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve based on the maximum temperature reached;
A process of allowing the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detecting the on of the ignition switch for starting the internal combustion engine;
The above-described problems can be solved by providing the structure.

  That is, the exhaust gas purification system and the control method thereof according to one aspect of the present invention are provided with the above-described configurations, so that the reducing agent injection valve and the reducing agent supply path are clogged or damaged due to solidification of the urea aqueous solution. As a result, it is possible to prevent a decrease in exhaust purification efficiency.

  The calculation of the melting temperature may be performed after the ignition switch is turned on. Alternatively, the melting temperature may be calculated after detecting the ignition switch OFF and before detecting the ON.

  The detection of the injection valve temperature of the reducing agent injection valve for specifying the maximum temperature reached may be performed in parallel with the recovery of the urea aqueous solution to the storage tank.

  The maximum temperature reached may be specified after the recovery of the urea aqueous solution into the storage tank.

  The calculation of the melting temperature may be performed based on the highest temperature reached and one or both of the temperature gradient of the reducing agent injection valve and the outside air temperature.

1 is an overall configuration diagram of an exhaust purification system according to an embodiment of the present invention. 1 is a block diagram of a control device provided in an exhaust purification system according to an embodiment of the present invention. It is a graph which shows an example of changes, such as a reducing agent injection valve temperature and a reducing agent solidification temperature, in an exhaust gas purification system concerning one embodiment of the present invention. It is a flowchart for demonstrating the exhaust gas purification system which concerns on one Embodiment of this invention, and its control method. It is a flowchart for demonstrating the exhaust gas purification system which concerns on one Embodiment of this invention, and its control method. It is a flowchart for demonstrating the exhaust gas purification system which concerns on one Embodiment of this invention, and its control method. It is a graph which shows the other example of changes, such as a reducing agent injection valve temperature and a reducing agent solidification temperature, in the exhaust gas purification system which concerns on one Embodiment of this invention. It is the graph showing the relationship between the density | concentration of urea aqueous solution, and solidification temperature T0.

  Hereinafter, embodiments of an exhaust purification system and a control method for an exhaust purification system according to the present invention will be specifically described 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 attaches | subjects the same code | symbol in each figure has shown the same member thru | or part, and description is abbreviate | omitted suitably.
1. Exhaust Purification System (1) Overall Configuration FIG. 1 is an overall configuration diagram of an exhaust purification system 10 according to an embodiment of the present invention.

  The exhaust purification system 10 performs 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, a forced regeneration control of the DPF 22, and an operation control of the reducing agent supply device 40. A control device 60 is provided as a main component.

Such an exhaust purification system 10 collects particulate matter (PM) in the exhaust gas by the DPF 22 and selectively uses the aqueous urea solution as the reducing agent to selectively remove NOx in the exhaust gas in the SCR catalyst 24. It is comprised as an apparatus for purifying.
(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 exhaust purification 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 NOx 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 NOx 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, a NOx 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.

  The sensor values of these sensors are sent to the control device 60, and the pressure, temperature, and NOx concentration at each position are 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. Via this connecting pipe 12, urea aqueous solution as a reducing agent is injected from the reducing agent injection valve 43 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, exhaust gas, or the like to the reducing agent injection valve 43.
(3) Forced regeneration means The exhaust purification system 10 of this embodiment includes forced regeneration means 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 forced regeneration is performed in which 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 configuration 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 The reducing agent supply device 40 includes a storage tank 41 that stores an aqueous urea solution, a pressure pump 42, and a reducing agent injection valve 43 as main components.

  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 exhaust purification system 10 of this embodiment has a configuration in which 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 T _lim is about 140 ° C. to 150 ° C., while the exhaust gas temperature during normal operation is 200 ° C. It is about 300 to 300 ° C.

  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.

  As a result, 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 thermal damage to the reducing agent injection valve 43 is prevented. Can be prevented.

  Further, in order to inject the reducing agent from the reducing agent injection valve 43, the relatively low temperature urea aqueous solution in the storage tank 41 is pumped to the reducing agent injection valve 43, so that the urea from the reducing agent injection valve 43 is reduced. The heat transfer to the aqueous solution also promotes heat dissipation of the reducing agent injection valve 43.

  The circulation of the engine cooling water and the heat radiation of the reducing agent injection valve 43 by heat transfer to the urea aqueous solution are performed particularly during the operation of the internal combustion engine 5.

This is because the engine coolant circulates during the operation of the internal combustion engine 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. Next, referring to FIG. 2, the control device 60 provided in the exhaust purification system 10 according to the embodiment of the present invention includes a temperature detection unit 62, a forced regeneration control unit 63, and the control device 60. The melting temperature calculation unit 64 and the injection valve operation permission unit 65 will be described in detail. Each of these units is typically realized by executing a program by a microcomputer.

  That is, FIG. 2 shows, in a functional block, a part related to control for eliminating clogging of the reducing agent injection valve 43 caused by solidification of the urea aqueous solution in the control device 60 provided in the exhaust purification system 10. This is a configuration example.

The control device 60 includes a signal of the ignition switch 57, each pressure sensor and each temperature sensor, a rotational speed sensor that detects the engine rotational speed Ne, a vehicle speed sensor that detects the vehicle speed V of the vehicle, and an accelerator pedal operation amount Acc. Various sensor signals such as an accelerator sensor to detect and a brake sensor to detect 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. Further, the control device 60 detects an on / off signal from the ignition switch 57 for starting and stopping the internal combustion engine. When the control device 60 detects the off signal, the control device 60 specifies the maximum temperature T _udvmax of the reducing agent injection valve 43. When the ON signal is detected, the operation of the reducing agent injection valve 43 is permitted after the temperature of the reducing agent injection valve 43 reaches the melting temperature T _str of the remaining reducing agent calculated from the maximum attained temperature T _udmax. It is configured as follows.

  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 NOx 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. That is, 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 signal for opening the reducing agent injection valve 43 and driving the pressure feed pump 42. Is output to the pressure feed pump 42 and the reducing agent injection valve 43 to recover the reducing agent present in the reducing agent injection valve 43 and the reducing agent supply path in the storage tank 41.
(2) Temperature detection part The temperature detection part 62 is for detecting the reducing agent injection valve temperature T _udv using the temperature sensor 53, but when it cannot be directly detected, the temperature T downstream of the DPF 22 in the vicinity thereof is detected. _It may be calculated or inferred from _dpf or the like.
(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.

Further, 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) Melting temperature calculation unit 64
When the melting temperature calculation unit 64 detects that the ignition switch 57 has been turned off to stop the internal combustion engine, the melting temperature calculation unit 64 starts detecting the injection valve temperature _Tudv of the reducing agent injection valve 43 through the temperature detection unit 62 and reduces the reducing agent. The maximum temperature T _udvmax of the injection valve 43 is specified.

Further, as described above, the "detection of the injection valve temperature _{T UDV",} in addition to detecting the injection valve temperature _{T UDV} directly calculated, for example, to infer from the DPF22 downstream temperature _{T dpf} etc. injector 43 near Including.

After the ignition switch 57 is turned off, when the engine 5 is stopped, in order to decrease the heat radiation efficiency of the cooling water circulation be stopped reducing agent injection valve 43 of an internal combustion engine 5, the injection valve temperature T _UDV is to some extent It rises over time and then falls.

Accordingly, the melting temperature calculation unit 64 _updates the injection valve maximum temperature T _max that is the maximum value of the injection valve temperature T _udv as the injection valve temperature T _udv increases, and the injection valve temperature T _{udv stops} increasing. the injection valve maximum temperature _{T max,} is identified as the highest temperature _{T Udvmax} of the reducing agent injection valve 43.

This maximum temperature T _udmax is used to calculate the solidification temperature (freezing point) T0, that is, the dissolution temperature (melting point) T _str , of the urea aqueous solution that is the reducing agent remaining in the reducing agent injection valve 43. 60 is stored in a predetermined storage means.

As described above, after the ignition switch 57 is turned off, the injection valve temperature T _udv rises, so the temperature of the urea aqueous solution remaining in the reducing agent injection valve 43 also rises, and the water content of the urea aqueous solution is vaporized to a concentration. As a result, the solidification temperature T0 of the residual urea aqueous solution, that is, the dissolution temperature _Tstr also increases.

Here, since the volume of the urea aqueous solution remaining in the reducing agent injection valve 43 after the reducing agent recovery processing (purge processing) is substantially constant according to the structure of the reducing agent injection valve 43, If the maximum temperature T _udmaxmax can be specified, the concentration of the concentrated residual aqueous urea solution can be calculated. Therefore, the solidification temperature T0, that is, the dissolution temperature T _{str of the} residual aqueous urea solution can also be calculated.

In addition, in the calculation of the concentration of the remaining urea aqueous solution, in addition to the maximum temperature T _udvmax of the reducing agent injection valve 43, various conditions unique to the actual machine to be implemented may affect the actual machine in advance. It is desirable that the concentration of the remaining urea aqueous solution can be calculated with sufficient accuracy simply by performing a test and specifying the maximum temperature T _udvmax .

For more accurate calculation, in addition to the maximum temperature _{T Udvmax} of the reducing agent injection valve 43, the highest temperature _T the temperature gradient of the reducing agent injection valve 43 upon reaching the _{udvmax δT udv,} outside air temperature T _It is preferable to calculate the concentration of the remaining urea aqueous solution and the solidification temperature T0, that is, the dissolution temperature _Tstr by appropriately combining _out and other conditions as necessary. That is, when the temperature gradient δT _udv is steep or the outside air temperature T _out is high, the concentration of the residual urea aqueous solution becomes higher, and the solidification temperature T0 of the residual urea aqueous solution, that is, the dissolution temperature T _str tends to be higher. Because there is.

  FIG. 3 is a graph showing an example of changes in the reducing agent injection valve temperature, the reducing agent solidification temperature, and the like in the exhaust purification system according to the embodiment of the present invention.

When the ignition switch 57 is turned off at time t1, the internal combustion engine 5 is stopped and the cooling water circulation of the internal combustion engine 5 is also stopped, so that the injection valve temperature T _udv rises over a certain period of time from that point. It can be seen that the temperature has decreased after reaching the maximum temperature T _udmax .

Further, as shown in FIG. 3, the solidification temperature T0 of the remaining urea aqueous solution rises so as to follow the rise of the injection valve temperature T _{uv with} a slight delay. As described above, this is due to the increase in the concentration of the remaining urea aqueous solution due to the increase in the injection valve temperature _Tudv .

When the injection valve temperature T _udv decreases and decreases to the solidification point that is the solidification temperature T0 of the residual urea aqueous solution at time t2, the residual urea aqueous solution of the reducing agent injection valve 43 is solidified, that is, solidified.

  FIG. 7 is a graph showing another example of changes in the reducing agent injection valve temperature, the reducing agent solidification temperature, and the like in an exhaust purification system according to another embodiment of the present invention.

In the example of FIG. 7, the forced regeneration control of the DPF 22 is started at a time t0 before the time t1 when the ignition switch 57 is turned off, and the accompanying increase in the injection valve temperature T _udv and the downstream temperature T _dpf of the DPF 22 However, the other points are almost the same as in the example of FIG.

Calculation of solidification temperature T0 i.e. melting temperature _{T str} of the urea aqueous solution, the maximum reachable from the temperature _{T Udvmax} of the urea aqueous solution concentration of the reducing agent injection valve 43 is calculated, the solidification temperature T0 i.e. melting temperature _{T str} corresponding to the concentration of the urea aqueous solution Is performed based on a characteristic map representing the relationship between the concentration of the urea aqueous solution and the solidification temperature T0, as in the graph of FIG. The characteristic map may be stored in a predetermined storage unit in the control device 60.

The calculation of the solidification temperature T0 of the residual urea aqueous solution, that is, the dissolution temperature _Tstr , may be performed after the ignition switch 57 for stopping the internal combustion engine is turned off until the power supply to the control device 60 is cut off. Alternatively, it may be performed when it is detected that the ignition switch 57 for starting the internal combustion engine is turned on after detecting that the ignition switch 57 is turned off.
(5) Injection valve operation permission unit When it is detected that the ignition switch 57 is turned on, the injection valve operation permission unit 65 starts detecting the injection valve temperature T _udv of the reducing agent injection valve 43 through the temperature detection unit 62. To do. As mentioned above, the "detection of the injection valve temperature _{T UDV",} in addition to measuring the injection valve temperature _{T UDV} directly, for example, also be calculated or inferred from DPF22 downstream temperature _{T dpf} etc. injector 43 near Including.

Then, the injection valve operation permission unit 65 determines whether to permit the operation of the reducing agent injection valve 43 based on the current injection valve temperature T _udv and the calculated dissolution temperature T _str of the remaining urea aqueous solution. To do. That is, depending on whether or not the current injection valve temperature T _udv has reached the dissolution temperature T _str of the remaining urea aqueous solution (T _udv ≧ T _str ), the injection valve operation permission unit 65 operates the reducing agent injection valve 43. It is determined whether or not to allow. When the operation permission determination by the injection valve operation permission unit 65 is made, the operation of the reducing agent injection valve 43 is started.

The reducing agent injection valve 43 does not inject the reducing agent until the operation permission determination by the injection valve operation permission unit 65 is made, but the SCR catalyst 24 of the exhaust purification unit 20 has The ammonia adsorbed during the previous operation remains, and the time until the start of the operation of the reducing agent injection valve 43 is relatively short. Usually, there is a problem that the environmental standard is not satisfied. Does not occur.
3. Control Method Hereinafter, a specific example of an exhaust purification system and a control method thereof according to an embodiment of the present invention will be described using a flowchart.

  FIG. 4 is a flowchart for explaining an exhaust purification system and a control method thereof according to an embodiment of the present invention, and in particular, a flowchart schematically showing the entire operation procedure of the control method of the exhaust purification system. .

First, when the control device 60, particularly the melting temperature calculation unit 64 detects that the ignition switch 57 is turned off (step S _<b> 1), the melting temperature calculation unit 64 sets the injection valve temperature T _udv of the reducing agent injection valve 43 through the temperature detection unit 62. Detection is started, and the maximum temperature T _udvmax is specified (step S2).

Thereafter, when the control device 60, in particular, the injection valve operation permission unit 65 detects that the ignition switch 57 is turned on (step S3), the injection valve operation permission unit 65 _calculates the reducing agent from the maximum temperature T _udvmax of the reducing agent injection valve 43. reducing agent remaining in the injection valve 43, in particular one to calculate the melting temperature T _str of the urea aqueous solution starts detecting the injection valve temperature T _UDV of the reducing agent injection valve 43 through the temperature detector 62 (step S4).

The injection valve operation permission unit 65 continuously compares the current injection valve temperature T _udv with the dissolution temperature T _str of the residual urea aqueous solution, and the injection valve temperature T _udv reaches the dissolution temperature T _str of the residual urea aqueous solution. (T _udv ≧ T _str ) or not (step S5).

When the injection valve operation permission unit 65 determines that the current injection valve temperature T _udv has reached the dissolution temperature T _str of the remaining urea aqueous solution, the injection valve operation permission unit 65 determines to permit the operation of the reducing agent injection valve 43 and Accordingly, the operation of the reducing agent injection valve 43 is started.

  Even when the urea aqueous solution once heated is solidified in the process of being cooled after the internal combustion engine is stopped, it is solidified by the operation procedure of the exhaust purification system and the control method thereof according to the embodiment of the present invention. By operating the reducing agent supply device after waiting for the urea aqueous solution to dissolve, it is possible to avoid clogging or breakage of the reducing agent injection valve or reducing agent supply path due to solidification of the urea aqueous solution. As a result, it is possible to prevent the exhaust purification efficiency from being lowered.

FIG. 5 is a flowchart for explaining an exhaust purification system and a control method thereof according to an embodiment of the present invention, and in particular, the highest temperature reached by the reducing agent injection valve 43 in response to detection of the ignition switch 57 being turned off. It is a flowchart which shows more specifically the operation _| movement procedure of the control method of the said exhaust gas purification system at the time of specifying _Tudvmax .

  First, when the control device 60 including the melting temperature calculation unit 64 detects that the ignition switch 57 is turned off (step S11), the control device 60 starts a reducing agent recovery process in the reducing agent supply device 40 provided in the exhaust purification system. (Step S12).

In addition, the melting temperature calculation unit 64 starts detecting the injection valve temperature T _udv of the reducing agent injection valve 43 through the temperature detection unit 62 in response to detection of the ignition switch 57 being turned off (step S13).

Specifically, “injection valve maximum temperature T _max = injection valve temperature T _udv ” is set, the injection valve temperature T _udv is continuously detected, and the current injection valve temperature T _udv and the injection valve maximum until then are detected. The temperature T _max is compared to determine whether or not the current injector valve temperature T _udv exceeds the injector injector maximum temperature T _max (T _udv > T _max ) (step S14).

When the current injection valve temperature T _udv exceeds the injection valve maximum temperature T _max so far, the injection valve temperature T _max is updated to “injection valve maximum temperature T _max = injection valve temperature T _{udv at the time} ”. _Continue detecting _udv .

On the other hand, when the current injection valve temperature T _udv no longer exceeds the injection valve maximum temperature T _max so far, it can be determined that the injection valve temperature T _udv will not further increase. T _max is specified as the maximum temperature T _udvmax reached by the reducing agent injection valve 43 and stored in a predetermined storage means in the control device 60 (step S15).

  Further, the control device 60 determines whether or not the reducing agent recovery process in the reducing agent supply device 40 provided in the exhaust purification system has been completed. When it is determined that the control device 60 has ended, the control device 60 supplies power to the control device 60 itself. A blocking process is performed, and the operation procedure is terminated (step S16).

Incidentally, the reducing agent recovery process is a normal that the injection valve temperature T _UDV of the reducing agent injection valve 43 is before reaching the injector maximum temperature T _max, it is terminated during the detection of the injection valve temperature T _UDV Therefore, the determination here is performed in order to confirm that the reducing agent recovery process has been reliably completed when the process of shutting off the power supply to the control device 60 is performed.

  FIG. 6 is a flowchart for explaining the exhaust purification system and the control method thereof according to the embodiment of the present invention. In particular, the operation of the reducing agent injection valve 43 is permitted in response to detection of the ignition switch 57 being turned on. It is a flowchart which shows more specifically the operation | movement procedure of the control method of the said exhaust gas purification system at the time of judgment.

When the control device 60 including the melting temperature calculation unit 64 and the injection valve operation permission unit 65 detects that the ignition switch 57 is turned on (step S21), the melting temperature calculation unit 64 is stored in a predetermined storage unit in the control device 60. The concentration C of the urea aqueous solution remaining and concentrated in the reducing agent injection valve 43 is _calculated from the maximum reached temperature T _udmax of the reducing agent injection valve 43, and the solidification temperature T0 of the residual urea aqueous solution, that is, the dissolution temperature, is calculated from the concentration C. T _str is calculated (step S22).

Calculation of solidification temperature T0 i.e. melting temperature T _str of the urea aqueous solution, the solidification temperature T0 i.e. melting temperature T _str corresponding to the concentration C of the remaining urea solution, similarly to the concentration of the urea aqueous solution and the graph of FIG. 8 and the solidification temperature T0 This is performed by specifying based on a characteristic map representing the relationship of The characteristic map is read from predetermined storage means in the control device 60.

On the other hand, the injection valve operation permission unit 65 starts detecting the injection valve temperature T _udv of the reducing agent injection valve 43 through the temperature detection unit 62 in response to the detection of the ignition switch 57 being turned on (step S22).

The injection valve operation permission unit 65 determines whether or not to permit the operation of the reducing agent injection valve 43 based on the current injection valve temperature T _udv and the calculated dissolution temperature T _{str of} the remaining urea aqueous solution. That is, depending on whether or not the current injection valve temperature T _udv has reached the dissolution temperature T _str of the remaining urea aqueous solution (T _udv ≧ T _str ), the injection valve operation permission unit 65 operates the reducing agent injection valve 43. It is determined whether or not to permit (step S23).

  When the operation permission is determined by the injection valve operation permission unit 65, the operation of the reducing agent injection valve 43 is started (step S24).

As described above, the calculation of the solidification temperature T0 of the residual urea aqueous solution, that is, the dissolution temperature T _str , may be performed when the ignition switch 57 is first detected after detecting the ignition switch 57 being turned off, or The process may be performed after detecting that the ignition switch 57 is turned off until the power supply to the control device 60 is interrupted, that is, between step S15 and step S16 in the flowchart of FIG.

  Even when the urea aqueous solution once heated is solidified in the process of being cooled after the internal combustion engine is stopped, the exhaust purification system according to the embodiment of the present invention shown in the flowcharts of FIGS. By operating the reducing agent supply device after waiting for the solidified urea aqueous solution to dissolve by such an operation procedure of the control method, the reducing agent injection valve and the reducing agent supply path are clogged due to the solidification of the urea aqueous solution. And damage can be avoided, and as a result, it is possible to prevent the exhaust purification efficiency from being lowered.

An exhaust purification system according to an aspect of the present invention includes a diesel particulate filter that collects exhaust particulates in exhaust gas of an internal combustion engine, and a urea aqueous solution as a reducing agent supplied from a storage tank to a reducing agent injection valve. When the internal combustion engine is stopped by being injected into the exhaust gas and supplied, the reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank, and the urea aqueous solution is used to supply the urea aqueous solution to the storage tank. An exhaust gas purification system comprising an SCR catalyst for purifying NOx of the exhaust gas sequentially from the exhaust upstream side,
After detecting the ignition switch OFF for stopping the internal combustion engine, the maximum reached temperature of the reducing agent injection valve is specified, and then the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve is determined. A dissolution temperature calculation unit for calculating based on the volume of the urea aqueous solution remaining in the injection valve and the maximum attained temperature;
An injection valve operation permission unit for permitting the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detection of turning on of an ignition switch for starting the internal combustion engine; ,
It is characterized by providing the control apparatus which has, and the said subject can be solved by providing the said structure.

Further, an exhaust purification system control method according to an aspect of the present invention includes:
A diesel particulate filter that collects exhaust particulates in the exhaust gas of an internal combustion engine and a urea aqueous solution as a reducing agent are supplied from the storage tank to the reducing agent injection valve by being injected and supplied into the exhaust gas. When the internal combustion engine is stopped, a reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank and an SCR catalyst that purifies NOx in the exhaust gas using the urea aqueous solution are exhausted upstream. In the exhaust purification system control method provided sequentially from the side,
A process of identifying the highest temperature reached by the reducing agent injection valve after detecting the ignition switch OFF for stopping the internal combustion engine;
Calculating the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve based on the volume of the urea aqueous solution remaining in the reducing agent injection valve and the maximum temperature reached;
A process of allowing the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detecting the on of the ignition switch for starting the internal combustion engine;
The above-described problems can be solved by providing the structure.

Claims (11)

A diesel particulate filter that collects exhaust particulates in the exhaust gas of an internal combustion engine and a urea aqueous solution as a reducing agent are supplied from the storage tank to the reducing agent injection valve by being injected and supplied into the exhaust gas. When the internal combustion engine is stopped, a reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank and an SCR catalyst that purifies NOx in the exhaust gas using the urea aqueous solution are exhausted upstream. In the exhaust purification system prepared sequentially from the side,
After detecting that the ignition switch for stopping the internal combustion engine is turned off, the maximum reached temperature of the reducing agent injection valve is identified, and then the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve is reached. A melting temperature calculation part for calculating based on the temperature;
An injection valve operation permission unit for permitting the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detection of turning on of an ignition switch for starting the internal combustion engine; ,
An exhaust purification system comprising a control device having   The exhaust purification system according to claim 1, wherein the melting temperature calculation unit performs the calculation of the melting temperature after detecting the ignition switch being turned on.   The exhaust purification system according to claim 1, wherein the melting temperature calculation unit calculates the melting temperature after detecting the ignition switch OFF and before detecting the ON.   The melting temperature calculation unit performs detection of the injection valve temperature of the reducing agent injection valve for specifying the maximum temperature reached in parallel with the recovery of the urea aqueous solution to the storage tank. Item 4. The exhaust gas purification system according to any one of Items 1 to 3.   The exhaust gas purification system according to any one of claims 1 to 4, wherein the melting temperature calculation unit specifies the maximum temperature reached after the recovery of the urea aqueous solution into the storage tank.   The said melting temperature calculation part performs calculation of the said melting temperature based on the one or both of the highest ultimate temperature, the temperature gradient of the said reducing agent injection valve, and external temperature. The exhaust gas purification system according to any one of claims 1 to 5. A diesel particulate filter that collects exhaust particulates in the exhaust gas of an internal combustion engine and a urea aqueous solution as a reducing agent are supplied from the storage tank to the reducing agent injection valve by being injected and supplied into the exhaust gas. When the internal combustion engine is stopped, a reducing agent supply device that recovers the urea aqueous solution in the supply path to the storage tank and an SCR catalyst that purifies NOx in the exhaust gas using the urea aqueous solution are exhausted upstream. In the exhaust purification system control method provided sequentially from the side,
A process of identifying the highest temperature reached by the reducing agent injection valve after detecting the ignition switch OFF for stopping the internal combustion engine;
Calculating the dissolution temperature of the urea aqueous solution remaining in the reducing agent injection valve based on the maximum temperature reached;
A process of allowing the operation of the reducing agent injection valve after the injection valve temperature of the reducing agent injection valve reaches the melting temperature after detecting the on of the ignition switch for starting the internal combustion engine;
A control method for an exhaust purification system, comprising:   The method of controlling an exhaust purification system according to claim 7, wherein the process of calculating the melting temperature is performed after detection of an ignition switch being turned on.   8. The method of controlling an exhaust purification system according to claim 7, wherein the process of calculating the melting temperature is performed after detecting that the ignition switch is turned off and before detecting that the ignition switch is turned on.   The detection of the injection valve temperature of the reducing agent injection valve for specifying the maximum temperature reached is performed in parallel with the recovery of the urea aqueous solution to the storage tank. The method for controlling an exhaust purification system according to one item.   The method for controlling an exhaust purification system according to any one of claims 7 to 10, wherein the maximum temperature reached is specified after the recovery of the urea aqueous solution into the storage tank.

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