JP2009097479A - Device and method for controlling reducing agent supplying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reducing agent supplying device capable of preventing the thermal damage to a reducer injection valve and crystallization of urea solution due to excessive cooling of liquid reducing agent, and a controlling method thereof. <P>SOLUTION: The reducing agent supplying device injects urea solution to an exhaust upstream side of reducing catalyst arranged in an exhaust passage of an internal combustion engine as the reducing agent, is used for an exhaust emission control device reducing/purifying nitrogen oxide in exhaust gas by the reducing catalyst, and equipped with a reducing agent injection valve fixed to an exhaust pipe on an exhaust upstream side of the reducing catalyst. The reducing agent supplying device comprises a cooling water circulating passage for circulating at least a part of cooling water in the internal combustion engine for cooling the reducing agent injection valve, a flow rate controlling means for adjusting the flow rate of the cooling water flowing in the cooling water circulating passage, a temperature detecting means for detecting the temperature of the reducing agent injection valve, and a controlling means for controlling the flow rate controlling means on the basis of the temperature of the reducing agent injection valve. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reducing agent supply device and a control method used in an exhaust purification device. In particular, the present invention relates to a reducing agent supply device configured to cool a reducing agent injection valve by using a urea solution as a reducing agent and circulating cooling water for cooling an internal combustion engine, and a control method for the reducing agent supply device.

Conventionally, in exhaust gas discharged from internal-combustion engine such as diesel engines, nitrogen oxides that may affect the environment (hereinafter, referred to as NO _X) are included. As an exhaust gas purification apparatus used to purify the NO _X, the liquid reducing agent urea solution or the like on the upstream side of the disposed in the exhaust passage reduction catalyst injected and supplied into the exhaust gas, NO _X in a reducing catalyst An exhaust gas purification device (SCR system) that selectively reduces and purifies is known.

As one aspect of such an exhaust purification device, the liquid reducing agent is pumped toward the reducing agent injection valve fixed to the exhaust pipe, and the reducing agent injection valve is controlled to open and close to supply the liquid reducing agent into the exhaust pipe. There is an exhaust purification device of the type. In such an exhaust purification apparatus, when a urea solution is used as a liquid reducing agent, if the urea solution becomes excessively high in temperature, the urea is hydrolyzed before the urea solution is injected from the reducing agent injection valve. In view of the possibility of partial or complete clogging of the liquid reducing agent supply system, sufficient urea solution supply rate and heat exchange fluid path to keep the temperature of the urea solution sufficiently low Accordingly, a method of reducing NO _X emissions was to pass the line or injector heat exchange fluid, such as engine coolant when the heat exchanger has been proposed (see Patent Document 1).

In addition, an electromagnetically controlled valve used as such a reducing agent injection valve is directly attached to the exhaust pipe even though its control part and resin part are relatively weak against heat, and thus heat damage is caused by heat transmitted from the exhaust pipe. It is easy to receive.
Therefore, there has been proposed a diesel engine exhaust gas purification device that can improve the durability of the injector for adding the reducing agent to the NO _x catalyst, although fuel (HC) is used as the reducing agent. More specifically, the NO _X catalyst interposed in an exhaust passage of the engine, a diesel engine equipped with an injector of the NO _X reducing agent additives provided upstream portion of the exhaust passage than the NO _X catalyst In the exhaust emission control device, a cooling water passage provided in the injector, a circulation passage connecting the cooling water passage and the engine cooling water passage, and the cooling water between the cooling water passage and the engine cooling water passage through the circulation passage. An exhaust emission control device provided with a circulation means for circulation is disclosed (see Patent Document 2).

JP-T-2001-518830 (Claim 11, page 8, line 7 to line 10) Japanese Patent Laid-Open No. 9-96212 (full text)

  However, when the reducing agent injection valve is cooled by circulating engine cooling water, the amount of engine cooling water circulating is relatively large, so that the reducing agent injection valve is efficiently cooled. In some cases, the reductant injection valve is cooled too much because of the large amount of circulation. As a result, in addition to urea crystallization caused by the urea solution becoming high temperature and being decomposed in the reducing agent supply system as noted in Patent Document 1, the solvent is present near the nozzle hole of the reducing agent injection valve. There is a risk of crystallization of urea due to spontaneous evaporation.

  That is, since the engine cooling water is maintained at, for example, about 70 to 80 ° C., when the circulation amount of the cooling water to be circulated with respect to the reducing agent injection valve is large, the temperature of the reducing agent injection valve is, for example, 80 to 80 ° C. It may be cooled to about 100 ° C. On the other hand, the urea aqueous solution flowing into the reducing agent supply valve is sent to the nozzle hole while being maintained at a temperature of less than 100 ° C. even if it is affected by the heat of the reducing agent injection valve. Therefore, since the urea aqueous solution injected from the reducing agent injection valve has a boiling point or less in the exhaust passage in a state close to atmospheric pressure, the urea aqueous solution is not quickly vaporized and easily adheres to the vicinity of the injection hole. The urea aqueous solution maintained at a temperature lower than 100 ° C. is in a state in which it is likely to cause precipitation due to spontaneous evaporation of water as a solvent in an environment relatively close to atmospheric pressure, and is exhausted near the nozzle hole of the reducing agent injection valve. The gas flow is also overlapped, and natural evaporation of water in the urea aqueous solution is more likely to occur, and the precipitation of urea is promoted. If the crystallization of urea in the vicinity of the nozzle hole of the reducing agent injection valve occurs, the spraying of the urea aqueous solution may be adversely affected and the nozzle hole may be clogged.

  Therefore, the inventors of the present invention have made diligent efforts and provided a means for controlling the circulation amount of the cooling water in the reducing agent supply device configured to circulate the cooling water of the engine to cool the urea solution. The present invention has been completed by finding that such problems can be solved. That is, an object of the present invention is to prevent the thermal damage of the reducing agent injection valve by adjusting the circulation amount of the cooling water according to the temperature of the reducing agent injection valve, and to prevent the urea solution from being overcooled. It is providing the reducing agent supply apparatus which can prevent crystallization, and its control method.

  According to the present invention, an exhaust gas purification apparatus that injects and supplies urea solution as a reducing agent to the exhaust upstream side of a reduction catalyst disposed in an exhaust passage of an internal combustion engine, and reduces and purifies nitrogen oxides in exhaust gas with the reduction catalyst. A reductant supply device having a reductant injection valve fixed to an exhaust pipe on the exhaust upstream side of the reduction catalyst, wherein at least part of the cooling water of the internal combustion engine for cooling the reductant injection valve A cooling water circulation passage for circulating the coolant, a flow rate control means for adjusting the flow rate of the cooling water flowing through the cooling water circulation passage, a temperature detection means for detecting the temperature of the reducing agent injection valve, and a reducing agent injection valve And a control means for controlling the flow rate control means based on the temperature. A reducing agent supply device is provided, which can solve the above-described problems.

  In configuring the reducing agent supply apparatus of the present invention, it is preferable that the control means controls the flow rate control means so that the temperature of the reducing agent injection valve is maintained below the heat resistant temperature of the reducing agent injection valve.

  In configuring the reducing agent supply apparatus of the present invention, it is preferable that the control means controls the flow rate control means so that the temperature of the reducing agent injection valve is maintained at or above the boiling point of the urea solution.

  Further, in configuring the reducing agent supply device of the present invention, the temperature detecting means includes the exhaust gas temperature, the exhaust gas flow rate, the liquid reducing agent temperature, the cooling water temperature, the outside air temperature, and the reducing agent injection valve. It is preferable to calculate the tip temperature of the reducing agent injection valve based on at least one of the injection supply amounts.

  In configuring the reducing agent supply apparatus of the present invention, the cooling water circulation passage, the flow rate control means, and the control means are respectively referred to as a first cooling water circulation passage, a first flow rate control means, and a first control means. A second cooling water circulation passage for circulating at least a part of the cooling water of the internal combustion engine to adjust the temperature of the urea solution in the storage tank for storing the urea solution, and a second cooling water circulation passage Second flow rate control means for adjusting the flow rate of the cooling water flowing through the storage tank, and second control means for controlling the second flow rate control means based on the temperature of the urea solution in the storage tank. It is preferable.

  Another aspect of the present invention is an exhaust purification system in which a liquid reducing agent is injected and supplied to an exhaust upstream side of a reduction catalyst disposed in an exhaust passage of an internal combustion engine, and nitrogen oxides in exhaust gas are reduced and purified by the reduction catalyst. A control method for a reducing agent supply device that is used in the apparatus and includes a reducing agent injection valve that is fixed to an exhaust pipe upstream of the reduction catalyst, wherein the reducing agent injection valve is at least one of cooling water for an internal combustion engine. The coolant is cooled by circulating the part, and the flow rate of the cooling water is controlled so that the temperature of the fuel injection valve is maintained within a predetermined range while detecting the temperature of the reducing agent injection valve. This is a control method for a reducing agent supply apparatus.

  According to the reducing agent supply apparatus of the present invention, the reducing agent injection valve can be efficiently cooled using the cooling water of the internal combustion engine, and the temperature of the reducing agent injection valve is detected while detecting the tip temperature of the reducing agent injection valve. Accordingly, since the flow rate of the cooling water can be adjusted, the reducing agent injection valve is prevented from being excessively cooled. Therefore, thermal damage to the reducing agent injection valve can be prevented, and urea crystallization in the vicinity of the injection hole of the reducing agent injection valve can be prevented, and stable spraying of the reducing agent can be realized.

  Further, in the reducing agent supply apparatus of the present invention, the control means controls the reducing agent injection valve so that the temperature of the reducing agent injection valve is maintained below the heat resistance temperature, thereby reliably preventing thermal damage to the reducing agent injection valve. Can do.

  In the reducing agent supply apparatus of the present invention, the control means performs control so that the temperature of the reducing agent injection valve is maintained at the boiling point or higher of the urea solution, whereby the urea solution exposed in the exhaust pipe is exhausted. In combination with this, it is possible to quickly vaporize and reliably prevent crystallization of urea in the vicinity of the nozzle hole.

  Further, in the reducing agent supply apparatus of the present invention, since the temperature detection means is a means for calculating the tip temperature of the reducing agent injection valve, the reduction is performed using the conventional apparatus configuration without newly using a temperature sensor. The tip temperature of the agent injection valve can be estimated.

  Further, in the reducing agent supply apparatus of the present invention, the temperature of the urea solution in the storage tank is adjusted using the cooling water of the internal combustion engine, so that the urea solution is injected from the reducing agent injection valve while the temperature is below the boiling point. It is possible to prevent crystallization of urea in the vicinity of the nozzle hole more reliably.

  Further, according to the control method for the reducing agent supply device of the present invention, when the reducing agent injection valve is cooled by circulating the cooling water of the internal combustion engine, the circulation amount of the cooling water is set based on the temperature of the reducing agent injection valve. By adjusting, it is possible to prevent thermal damage to the reducing agent injection valve and to prevent crystallization of urea due to excessive cooling of the reducing agent injection valve. Therefore, stable spraying of the reducing agent can be realized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments relating to a reducing agent supply apparatus and a reducing agent supply apparatus control method according to the present invention will be specifically described below with reference to the drawings. However, this 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, in each figure, what has attached | subjected the same code | symbol has shown the same member, and description is abbreviate | omitted suitably.

1. Exhaust Purification Device First, an example of the configuration of an exhaust purification device provided with the reducing agent supply device of the present embodiment will be described with reference to FIG.
The exhaust purification device 10 shown in FIG. 1 injects and supplies a urea aqueous solution as a liquid reducing agent to the upstream side of the reduction catalyst 13 disposed in the exhaust passage, and the NO _x contained in the exhaust gas in the reduction catalyst 13. Is an exhaust purification device 10 that selectively reduces and purifies the exhaust gas. The exhaust purification device 10 is disposed in the middle of an exhaust pipe 11 connected to the internal combustion engine 5, and a reduction catalyst 13 for selectively reducing NO _x contained in the exhaust gas, and an upstream of the reduction catalyst 13. The main component is a reducing agent supply device 20 including a reducing agent injection valve 31 for injecting and supplying an aqueous urea solution into the exhaust pipe 11 on the side.

2. Reducing agent supply device A reducing agent supply device 20 provided in the exhaust purification device 10 of the present embodiment stores a reducing agent injection valve 31 fixed to the exhaust pipe 11 on the upstream side of the reduction catalyst 13 and a urea aqueous solution. In order to control the storage tank 50, the pump module 40 including the pump 41 that pumps the urea aqueous solution in the storage tank 50 to the reducing agent injection valve 31, and the injection amount of the reducing agent injected and supplied into the exhaust pipe 11. A control device (hereinafter referred to as “DCU: Dosing Control Unit”) 60 for controlling the reducing agent injection valve 31 and the pump 41 is provided. The pump module 40 and the reducing agent injection valve 31 are connected by a first supply passage 58, the storage tank 50 and the pump module 40 are connected by a second supply passage 57, and the pump module 40 and the storage tank. 50 is connected by a circulation passage 59.

  As the reducing agent injection valve 31, for example, an ON-OFF valve whose ON / OFF is controlled by DUTY control can be used. The aqueous urea solution pumped from the pump module 40 to the reducing agent injection valve 31 is maintained at a predetermined pressure. When the reducing agent injection valve 31 is opened by a control signal sent from the DCU 60, the urea solution The aqueous solution is injected into the exhaust passage.

  The reducing agent injection valve 31 is provided with a cooling water passage 37 so that the reducing agent injection valve 31 is cooled using the cooling water of the internal combustion engine 5. In the example of the reducing agent supply device 20 in the present embodiment, the first cooling water circulation passage 85 including the cooling water passage 37 of the reducing agent injection valve 31 is provided, and the cooling water of the internal combustion engine 5 is internalized by the cooling water circulation pump 73. While circulating through the cooling water passage 75 of the engine 5, it branches from the cooling water passage 75 and also flows into the first cooling water circulation passage 85. The cooling water flowing into the first cooling water circulation passage 85 passes through the cooling water passage 37 provided in the reducing agent injection valve 31 and is returned to the cooling water passage 75 of the internal combustion engine 5 again. 31 is cooled.

  A first coolant flow control valve 81 for adjusting the flow rate of the coolant flowing through the first coolant circulation passage 85 is provided upstream of the reducing agent injection valve 31 in the first coolant circulation passage 85. It has been. As the first cooling water flow rate control valve 81, for example, an electromagnetic control type ON-OFF valve or an electromagnetic proportional flow rate control valve can be used, which is controlled by the DCU 60 described later. The first coolant flow control valve 81 is normally opened, and the reducing agent injection valve 31 is cooled by the coolant. On the other hand, when the reducing agent injection valve 31 may be cooled too much, the first cooling water flow rate control valve 81 is closed to interrupt the circulation of the cooling water, or the first cooling water flow rate control is performed. The flow rate of the cooling water is decreased by decreasing the opening degree of the valve 81, and the reducing agent injection valve 31 is adjusted so as not to be cooled too much.

  A temperature sensor for detecting the temperature of the urea aqueous solution flowing into the reducing agent injection valve 31 is provided at the inlet of the reducing agent injection valve 31 in the first supply passage 58 connected to the reducing agent injection valve 31. 33 is provided. Furthermore, a temperature sensor 35 for detecting the temperature of the cooling water flowing into the reducing agent injection valve 31 is provided in the inlet portion of the first cooling water circulation passage 85 on the upstream side of the reducing agent injection valve 31. Yes. The temperature information detected by these temperature sensors 33 and 35 is sent to the DCU 60.

  Further, in the reducing agent supply device 20 of the present embodiment, the second coolant is further supplied from the upstream side of the first coolant flow control valve 81 in the first coolant circulation passage 85 branched from the coolant passage 75 of the internal combustion engine 5. The cooling water circulation passage 87 is branched. The second cooling water circulation passage 87 is disposed so as to pass through the storage tank 50, and joins the first cooling water circulation passage 85 again. Further, a second cooling water flow rate control valve 83 for adjusting the flow rate of the cooling water flowing through the second cooling water circulation passage 87 is provided upstream of the storage tank 50 in the second cooling water circulation passage 87. ing.

The cooling water of the internal combustion engine 5 that circulates in the second cooling water circulation passage 87 is used as a heating means for the urea aqueous solution in the storage tank 50. Since the cooling water of the internal combustion engine 5 is maintained at, for example, about 70 to 80 ° C., the second cooling water flow rate control valve 83 is opened when the temperature of the urea aqueous solution in the storage tank 50 decreases. The cooling water is circulated in the storage tank 50 and controlled so that the temperature of the urea aqueous solution does not decrease excessively and the urea aqueous solution does not freeze.
Similarly to the first cooling water flow rate control valve 81, the second cooling water flow rate control valve 83 can use an electromagnetically controlled ON-OFF valve or an electromagnetic proportional flow rate control valve, and is controlled by the DCU 60. It has become so. That is, the storage tank 50 in which the urea aqueous solution is stored is provided with a temperature sensor 51 for detecting the temperature of the urea aqueous solution in the tank, and the value detected by the temperature sensor 51 is a signal to the DCU 60. The second coolant flow control valve 83 is controlled based on this temperature information.

The pump module 40 is provided with a pump 41, which pumps up the urea aqueous solution in the storage tank 50 through the second supply passage 57 and pumps it to the reducing agent injection valve 31 through the first supply passage 58. It is like that. The pump 41 is composed of an electric gear pump, for example, and can be DUTY controlled by a signal sent from the DCU 60. Further, the first supply passage 58 is provided with a pressure sensor 43, and a value detected by the pressure sensor 43 is output as a signal to the DCU 60, and the pressure value in the first supply passage 58 is maintained at a predetermined value. As a result, the drive DUTY of the pump 41 is controlled. That is, in a state where the pressure in the first supply passage 58 is lower than a predetermined value, the drive DUTY of the pump 41 is controlled to increase, and the pressure in the first supply passage 58 is lower than the predetermined value. In such a state that also rises, the drive DUTY of the pump 41 is controlled to be small.
Note that “pump drive DUTY” means the ratio of pump drive time per cycle in PWM (pulse width modulation) control.

  In addition, the first supply passage 58 is provided with a main filter 47 so that foreign substances in the urea aqueous solution pumped to the reducing agent injection valve 31 are collected. A circulation passage 59 is branched from the first supply passage 58 between the pump 41 and the main filter 47 and is connected to the storage tank 50. An orifice 45 is provided in the middle of the circulation passage 59, and a pressure control valve 49 is provided closer to the storage tank 50 than the orifice 45. By providing such a circulation passage 59, the pressure value in the first supply passage 58 is a predetermined value in a state where the urea aqueous solution is pumped by the pump 41 that is feedback-controlled based on the detection value of the pressure sensor 43. When the pressure exceeds the value, the pressure control valve 49 is opened so that a part of the urea aqueous solution is recirculated into the storage tank 50. As the pressure control valve 49, for example, a known check valve or the like can be used.

Further, the pump module 40 is provided with a reverting valve 71, and when the reducing agent supply device 20 does not perform the injection control of the urea aqueous solution, the pump module 40, the reducing agent injection valve 31, the first supply passage 58, The reducing agent supply system urea aqueous solution including the second supply passage 57 and the like can be recovered in the storage tank 50. Accordingly, when the internal combustion engine 5 is stopped and the reducing agent supply device 20 is not controlled under a temperature condition in which the aqueous urea solution is likely to freeze, such as in cold weather, the urea aqueous solution in the reducing agent supply system is not used. When freezing is prevented and then the operation of the internal combustion engine is resumed, there is no injection failure due to clogging.
The reverting valve 71 is, for example, a switching valve having a function of switching the flow path of the urea aqueous solution from the forward direction from the storage tank 50 to the pump module 40 to the reverse direction from the pump module 40 to the storage tank 50. When the ignition switch of the internal combustion engine is turned off, the urea aqueous solution can be recovered in the storage tank 50 by switching the flow path in the reverse direction.

Each part of the reducing agent supply system of the reducing agent supply apparatus 20 is provided with heaters 92 to 97, respectively. When the aqueous urea solution is present in the reducing agent supply system during cold weather or the like, these heaters 92 to 97 freeze the urea aqueous solution partially or completely to block the reducing agent supply system. It is provided in order to prevent the injection control of the reducing agent by the injection valve 31 from being performed accurately. In addition, energization of these heaters 92 to 97 is controlled by the DCU 60. For example, when the reducing agent supply system determines that the urea aqueous solution is freezing based on the temperature of the aqueous urea solution or the outside air temperature, the battery is supplied with voltage and heated. It has become so.
These heaters 92 to 97 are not particularly limited, and for example, a heating wire can be used.

3. Reducing agent supply unit control unit (DCU)
FIG. 2 shows a configuration of the DCU 60 for controlling the reducing agent supply apparatus of the present embodiment. The DCU 60 is configured with a microcomputer having a known configuration as the center, and functionally controls a part related to operation control of the first cooling water flow rate control valve 81 and the second cooling water flow rate control valve 83 in FIG. An example of the configuration shown in each block is shown.
The DCU 60 in the present embodiment includes an injection valve temperature detection unit (indicated as “Injector-Temp detection”) that detects the temperature of the reducing agent injection valve, and a first control unit that controls the first coolant flow control valve ( The main components are an “Injector-Cooling control” and a second control unit (described as “Tank-Heating control”) for controlling the second cooling water flow rate control valve. Each of these units is specifically realized by executing a program by a microcomputer (not shown).

Among these, the injection valve temperature detection part detects the temperature of a reducing agent injection valve, and sends temperature information to a 1st control part. The method for detecting the temperature of the reducing agent injection valve is not particularly limited, and the reducing agent injection valve may be directly detected by providing a temperature sensor, or may be estimated by calculation.
In the DCU 60 of the present embodiment, the injection valve temperature detection unit flows into the exhaust gas temperature Tg and the exhaust gas flow rate Ve estimated from the operating state of the internal combustion engine, the temperature Tu1 of the urea aqueous solution in the storage tank, and the reducing agent injection valve. Based on the information on the temperature Tu2 of the urea aqueous solution, the temperature Tr of the cooling water flowing into the reducing agent injection valve, the outside air temperature To, the injection instruction value Qu sent from the DCU 60 to the reducing agent injection valve, and the vehicle speed S, The tip temperature Ti of the reducing agent injection valve is estimated.

The tip temperature Ti of the reducing agent injection valve is estimated by the injection valve temperature detection part because the flow rate of the cooling water is determined based on the temperature near the injection hole where urea crystallization is likely to occur due to evaporation of water in the urea aqueous solution. This is because it can be controlled. In addition, the reducing agent injection valve is heated by exhaust heat transmitted through the exhaust pipe. If the temperature of the tip of the reducing agent injection valve, which is the highest temperature, is kept below the heat-resistant temperature. This is because the entire reducing agent injection valve can be kept at a heat resistant temperature or lower.
In estimating the tip temperature Ti of the reducing agent injection valve, it is not necessary to refer to all the information described above, and it may be estimated based on some of the information.

The first control unit that controls the first cooling water flow rate control valve uses the first cooling water based on the tip temperature Ti of the reducing agent injection valve sent from the injection valve temperature detection unit. A control signal for opening and closing the flow control valve is output.
For example, during normal operation of the internal combustion engine, the first cooling water flow rate control valve is opened so that a relatively large amount of cooling water is first cooled so that the tip temperature Ti of the reducing agent injection valve is maintained below the heat resistance temperature. The water circulation passage 85 is circulated. The tip temperature Ti for setting the resin part of the reducing agent injection valve and the electromagnetic control unit to the heat resistant temperature or less varies depending on the type of the reducing agent injection valve. For example, the tip temperature Ti is maintained at 140 to 160 ° C. or less. Circulate the cooling water.
On the other hand, if the reducing agent injection valve is cooled too much by the cooling water, urea may be crystallized in the vicinity of the nozzle hole, so the first cooling water flow control valve is closed to shut off the cooling water, or Reduce the flow rate of cooling water by reducing the opening. For example, in order to quickly evaporate and vaporize the urea aqueous solution injected through the nozzle hole, the cooling water is maintained so that the tip temperature Ti of the reducing agent injection valve is maintained at the boiling point or higher of the urea aqueous solution. Adjust the flow rate. Although the boiling point of the urea aqueous solution varies depending on the concentration, for example, the flow rate of the cooling water is adjusted so that the tip temperature Ti is maintained at 100 to 110 ° C. or higher.

That is, in the first control unit in the DCU 60 of the present embodiment, the tip temperature Ti of the reducing agent injection valve is determined based on the information on the tip temperature Ti of the reducing agent injection valve sent from the injection valve temperature detection unit. The opening and closing of the first cooling water flow rate control valve is feedback-controlled so that the boiling point of the urea aqueous solution in the exhaust passage is equal to or higher than the heat resistance temperature of the reducing agent injection valve. As a result, thermal damage to the reducing agent injection valve is prevented and durability is improved, and urea crystallization is prevented in the vicinity of the injection hole of the reducing agent injection valve, thereby enabling stable spraying of the urea aqueous solution.
In the example of the present embodiment, control is performed so that the tip temperature Ti of the reducing agent injection valve is equal to or higher than the boiling point of the urea aqueous solution, but the urea aqueous solution is quickly vaporized under the influence of exhaust heat after injection. If so, the tip temperature Ti may be less than the boiling point of the urea aqueous solution.

Further, the second control unit outputs a control signal for opening and closing the second cooling water flow rate control valve based on the temperature of the urea aqueous solution detected by a temperature sensor provided in the storage tank. It has become.
For example, when the temperature of the aqueous urea solution in the storage tank falls below freezing point, the aqueous urea solution freezes and cannot be supplied to the reducing agent injection valve. Even when the temperature is below the freezing point, if the temperature is, for example, 80 ° C. or higher, the urea aqueous solution may be altered.
Therefore, in the second control unit in the DCU 60 of the present embodiment, when the temperature of the urea aqueous solution in the storage tank is less than 60 ° C., the urea aqueous solution in the storage tank is heated by opening the second cooling water flow rate control valve. Thus, freezing of the urea aqueous solution is prevented. On the other hand, when the temperature of the urea aqueous solution in the storage tank becomes 60 ° C. or higher, the heating by the cooling water of the internal combustion engine is stopped by closing the second cooling water flow rate control valve, and the alteration of the urea aqueous solution in the storage tank is performed. Is prevented.

4). Reducing Agent Injection Control Next, reducing agent injection control performed by the reducing agent supply device 20 provided in the exhaust purification device 10 of FIG. 1 will be described.
During operation of the internal combustion engine, the liquid reducing agent in the storage tank 50 is pumped up by the pump 41 and pumped to the reducing agent injection valve 31. At this time, the detection value by the pressure sensor 43 provided in the first supply passage 58 on the downstream side of the pump 41 is fed back and controlled to show a predetermined pressure value. For example, when the detected value is less than a predetermined value, the output of the pump 41 is increased. On the other hand, when the pressure value exceeds the predetermined value, the output of the pump 41 is decreased and the liquid reducing agent is stored via the pressure control valve 49. It is returned to the tank 50 and depressurized. As a result, the pressure of the reducing agent pumped toward the reducing agent injection valve 31 is maintained at a substantially constant value.

Further, the reducing agent pumped from the pump module 40 to the reducing agent injection valve 31 is maintained at a substantially constant pressure value, and is injected into the exhaust passage when the reducing agent injection valve 31 is opened. ing. The DCU 60 is based on information such as the operating state of the internal combustion engine, the exhaust temperature, the temperature of the reduction catalyst 13, and the amount of NO _x that has passed through the reduction catalyst 13 without being reduced, measured on the downstream side of the reduction catalyst 13. The amount of reducing agent to be injected is determined, and a control signal corresponding to the amount is generated and output to the reducing agent injection valve 31. The reducing agent injection valve 31 is subjected to DUTY control by this control signal, and an appropriate amount of reducing agent is injected and supplied into the exhaust passage. The reducing agent injected into the exhaust passage flows into the reduction catalyst 13 and is used for the reduction reaction of NO _x contained in the exhaust gas.

5). Cooling Water Circulation Control Next, an example of a cooling water circulation control routine by the control unit (DCU) 60 of the reducing agent supply apparatus of the present embodiment shown in FIG. 2 will be described with reference to the control flow shown in FIGS. explain.

  First, as shown in FIG. 3, in step S1 after the start, the temperature of the reducing agent injection valve is detected. As described above, in the DCU 60 of the present embodiment, the exhaust gas temperature Tg, the flow rate Ve of the exhaust gas, the temperature Tu1 of the urea aqueous solution in the storage tank, the temperature Tu2 of the urea aqueous solution flowing into the reducing agent injection valve, the reducing agent injection valve The tip temperature Ti of the reducing agent injection valve is calculated on the basis of the information on the temperature Tr of the cooling water flowing in, the outside air temperature To, the injection command value Qu sent from the DCU 60 to the reducing agent injection valve, and the vehicle speed S. The

  Next, in step S2, it is determined whether or not the detected tip temperature Ti of the reducing agent injection valve is lower than a lower limit value Ti1. In the present embodiment, the lower limit value Ti1 is set to the boiling point of the urea aqueous solution. If the tip temperature Ti of the reducing agent injection valve is less than the lower limit Ti1, the process proceeds to step S3, where the first cooling water flow rate control valve is fully closed or the opening degree is decreased, and then the start is started. Returned. As a result, the flow rate of the cooling water flowing through the cooling water passage provided in the reducing agent injection valve is reduced, and the tip temperature Ti of the reducing agent injection valve rises due to the influence of the exhaust heat transmitted by the exhaust pipe. .

  On the other hand, when the tip temperature Ti of the reducing agent injection valve is not less than the lower limit value Ti1 in step S2, the process proceeds to step S4, and whether or not the tip temperature Ti of the reducing agent injection valve is not less than the upper limit value Ti2. Is determined. In the present embodiment, the upper limit value Ti2 is set to the heat resistant temperature of the reducing agent injection valve. Then, when the tip temperature Ti of the reducing agent injection valve is less than the upper limit value Ti2, the process returns to the start as it is, whereas when the tip temperature Ti is equal to or higher than the upper limit value Ti2, the process proceeds to step S5. After the first coolant flow control valve is fully opened or the opening degree is increased, the operation is returned to the start. As a result, the flow rate of the cooling water flowing through the cooling water passage provided in the reducing agent injection valve increases, the reducing agent injection valve is cooled, and the tip temperature Ti decreases.

In the control method of the reducing agent supply device of the present embodiment, the opening / closing control of the second coolant flow control valve is performed together with the temperature control of the reducing agent injection valve by the opening / closing control of the first cooling water flow control valve described above. Temperature control of the urea aqueous solution in the storage tank is performed.
FIG. 4 shows a flow of temperature control of the aqueous urea solution in the storage tank. First, in step S11, the temperature Tu1 of the aqueous urea solution in the storage tank is detected. In the case of the reducing agent supply device of this embodiment, temperature information detected by a temperature sensor arranged in the storage tank is read.

Next, in step S12, it is determined whether or not the detected temperature Tu1 of the urea aqueous solution is equal to or lower than a reference value Tu0. The reference value Tu0 at this time is set to 60 ° C., for example, with reference to the temperature at which the urea aqueous solution in the storage tank is maintained without being altered.
When the temperature Tu1 of the urea aqueous solution is equal to or lower than the reference value Tu0, the process proceeds to step S13, where the second cooling water flow rate control valve is fully opened or the opening degree is increased, and then returned to the start. As a result, the urea aqueous solution in the storage tank is heated by the cooling water of the internal combustion engine maintained at 70 to 80 ° C.

On the other hand, if the detected temperature Tu1 of the urea aqueous solution exceeds the reference value Tu0, the temperature of the urea aqueous solution in the storage tank may be excessively increased and deteriorated. The cooling water flow rate control valve is fully closed or the opening degree is decreased, and then returned to the start.
Thus, by controlling so that the temperature of the urea aqueous solution in the storage tank is maintained within a range of, for example, 60 to 80 ° C., the urea aqueous solution is prevented from freezing and denatured, and from the reducing agent injection valve. When it is injected, it is quickly vaporized and easily dispersed uniformly in the exhaust gas.
In the example of the opening / closing control of the second cooling water flow rate control valve in this embodiment, the flow rate control is performed only by determining whether the temperature Tu1 of the urea aqueous solution exceeds or does not exceed the reference value Tu0. The second reference value Tu2 different from the reference value Tu0 is determined, the temperature range of the urea aqueous solution in the storage tank is further subdivided, and the cooling control of the urea aqueous solution in the storage tank is performed by the cooling water of the internal combustion engine You may do it.

It is a figure which shows the structural example of an exhaust gas purification apparatus. It is a block diagram which shows the structural example of the reducing agent supply apparatus control apparatus (DCU) with which the exhaust gas purification apparatus was equipped. It is a flowchart which shows an example of the temperature control of the reducing agent injection valve using the cooling water of an internal combustion engine. It is a flowchart which shows an example of the temperature control of the urea aqueous solution using the cooling water of an internal combustion engine.

Explanation of symbols

10: exhaust purification device, 11: exhaust pipe, 13: reduction catalyst, 15 · 16: temperature sensor, 17: NO _X sensor, 20: reducing agent supply device, 31: reducing agent injection valve, 33/35: temperature sensor, 40: pump module, 41: pump, 43: pressure sensor, 45: orifice, 47: main filter, 49: pressure control valve, 50: storage tank, 51: temperature sensor, 57: second supply passage, 58: first 1 supply passage, 59: circulation path, 60: reducing agent supply device control unit (DCU), 71: reverting valve, 73: cooling water circulation pump, 75: cooling water passage of internal combustion engine, 81: first cooling water Flow control valve, 83: second cooling water flow control valve, 85: first cooling water circulation passage, 87: second cooling water circulation passage, 92, 93, 94, 95, 96, 97: heater

Claims (6)

A urea solution is injected and supplied as a reducing agent to the exhaust upstream side of a reduction catalyst disposed in an exhaust passage of an internal combustion engine, and is used in an exhaust purification device that reduces and purifies nitrogen oxides in exhaust gas with the reduction catalyst, In the reducing agent supply device provided with the reducing agent injection valve fixed to the exhaust pipe on the exhaust upstream side of the reduction catalyst,
A cooling water circulation passage for circulating at least a part of the cooling water of the internal combustion engine to cool the reducing agent injection valve;
Flow rate control means for adjusting the flow rate of the cooling water flowing through the cooling water circulation passage;
Temperature detecting means for detecting the temperature of the reducing agent injection valve;
Control means for controlling the flow rate control means based on the temperature of the reducing agent injection valve;
A reducing agent supply device comprising:   2. The reducing agent supply apparatus according to claim 1, wherein the control unit controls the flow rate control unit so that a temperature of the reducing agent injection valve is maintained below a heat resistant temperature of the reducing agent injection valve. .   3. The reducing agent supply apparatus according to claim 1, wherein the control unit controls the flow rate control unit so that a temperature of the reducing agent injection valve is maintained at a temperature equal to or higher than a boiling point of the urea solution.   The temperature detection means is at least one of the temperature of the exhaust gas, the flow rate of the exhaust gas, the temperature of the liquid reducing agent, the temperature of the cooling water, the outside air temperature, and the injection supply amount from the reducing agent injection valve. The reducing agent supply apparatus according to any one of claims 1 to 3, wherein a tip temperature of the reducing agent injection valve is calculated based on the flow rate. When the cooling water circulation passage, the flow rate control means, and the control means are respectively a first cooling water circulation passage, a first flow rate control means, and a first control means,
A second cooling water circulation passage for circulating at least a portion of the cooling water of the internal combustion engine to adjust the temperature of the urea solution in a storage tank for storing the urea solution;
Second flow rate control means for adjusting the flow rate of the cooling water flowing through the second cooling water circulation passage;
Second control means for controlling the second flow rate control means based on the temperature of the urea solution in the storage tank;
The reducing agent supply device according to any one of claims 1 to 4, further comprising: The reduction catalyst is used in an exhaust purification device that injects and supplies a liquid reducing agent to the exhaust upstream side of a reduction catalyst disposed in an exhaust passage of an internal combustion engine, and reduces and purifies nitrogen oxides in the exhaust with the reduction catalyst. In the control method of the reducing agent supply device provided with the reducing agent injection valve fixed to the exhaust pipe on the exhaust upstream side of
The reducing agent injection valve is cooled by circulating at least a part of the cooling water of the internal combustion engine,
A control method for a reducing agent supply device, wherein the temperature of the reducing agent injection valve is detected and the flow rate of the cooling water is controlled so that the temperature of the fuel control valve is maintained within a predetermined range.

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