Urea removal device

Abstract

A urea removal device (2) includes: a determination unit (221) that determines whether urea aqueous solution (N) is injected from the injection nozzle (13) when executing control to inject urea aqueous solution (N) from the injection nozzle (13) into the exhaust pipe (12) through which the exhaust gas flows from the engine (11); a supply control unit (222) that controls a pump (15) that supplies urea aqueous solution (N) from a tank (14) storing urea aqueous solution (N) to the injection nozzle (13), and supplies urea aqueous solution (N) from the tank (14) to the injection nozzle (13) if it is determined that urea aqueous solution is not injected from the injection nozzle (13); and a temperature control unit (223) that executes control to raise the temperature of the exhaust gas when the urea aqueous solution (N) supplied from the tank (14) has been injected into the injection nozzle (13).

Description

Technical Field

[0001] This invention relates to a urea removal device for removing urea adhering to a spray nozzle that sprays an aqueous urea solution. Background Technology

[0002] Techniques for reducing nitrogen oxides (NOx) by injecting an aqueous urea solution into engine exhaust are known. Patent Document 1 discloses a technique for removing residual aqueous urea solution in an injection nozzle by injecting pressurized air after injecting the aqueous urea solution from the nozzle.

[0003] Existing technology

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-31746 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] However, even when pressurized air is injected, urea solution can sometimes undesirably remain in the injection nozzle. Heating this urea solution in the nozzle can lead to urea precipitation and adhesion problems.

[0008] The present invention was made in view of these problems, and the object of the present invention is to make it easier to remove urea adhering to the injection nozzle.

[0009] means for solving problems

[0010] One aspect of the present invention provides a urea removal apparatus, comprising: a determination unit that determines whether an aqueous urea solution is being injected from an injection nozzle when executing control to inject an aqueous urea solution from an injection nozzle into an exhaust pipe through which engine exhaust gases flow; a supply control unit that controls a pump that supplies an aqueous urea solution from a tank to the injection nozzle, and, if it is determined that the aqueous urea solution is not being injected from the injection nozzle, supplies the aqueous urea solution from the tank to the injection nozzle; and a temperature control unit that, when the aqueous urea solution supplied from the tank has been injected into the injection nozzle, executes control to raise the temperature of the exhaust gases.

[0011] The temperature control unit can perform control to raise the temperature of the exhaust gas, so that the temperature of the urea aqueous solution injected into the injection nozzle is equal to or higher than the lower limit temperature of the water solubility of urea, which is the predetermined solubility limit temperature.

[0012] The temperature control unit can perform control to raise the temperature of the exhaust gas, so that the temperature of the urea aqueous solution injected into the injection nozzle is equal to or higher than the lower limit temperature, and additionally, make the temperature of the injection nozzle lower than the upper limit temperature based on the heat resistance temperature of the injection nozzle, wherein the upper limit temperature is higher than the lower limit temperature.

[0013] The temperature control unit can continuously control the fuel injection unit, which injects fuel into the engine's combustion chamber, to perform multiple fuel injections during one combustion cycle of the engine, thereby raising the temperature of the exhaust gas.

[0014] The supply control unit can perform control to supply urea aqueous solution to the injection nozzle, and simultaneously implement diagnostic control to determine whether the purification device for purifying exhaust gas is operating normally. When injection control is performed to inject urea aqueous solution into the injection nozzle by applying an injection voltage, the determination unit can determine that urea aqueous solution is being injected from the injection nozzle if: the difference between the maximum and minimum values ​​of a function representing the time change of the current value from the time the injection voltage is applied to the injection nozzle until the determination time has elapsed; and if the difference is less than the determination threshold, it is determined that urea aqueous solution is not being injected from the injection nozzle.

[0015] After starting control to raise the temperature of the exhaust gas, an injection voltage is applied to the injection nozzle, and if the difference observed when the injection voltage is applied is equal to or greater than the determination threshold, the determination unit can determine that the urea aqueous solution is being injected from the injection nozzle.

[0016] The determination unit can continue to apply injection voltage to the injection nozzle after starting control to raise the temperature of the exhaust gas, and when the determination unit determines that the urea aqueous solution is injected from the injection nozzle, the temperature control unit can end the control to raise the temperature of the exhaust gas.

[0017] Once the waiting time required for the urea solution to be injected into the injection nozzle has elapsed since the start of the supply of the urea solution to the injection nozzle, the temperature control unit can begin to control the temperature of the exhaust gas to rise.

[0018] The effects of the invention

[0019] The present invention has the advantage of being able to more easily remove urea adhering to the injection nozzle. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the configuration of a purification system for purifying waste gas.

[0021] Figure 2 This is a table showing the relationship between the water solubility of urea and temperature.

[0022] Figure 3 This is a schematic diagram used to illustrate the control of raising the temperature of exhaust gas.

[0023] Figure 4 This is a flowchart illustrating an example of the urea removal process.

[0024] Explanation of reference numerals in the attached figures

[0025] S: Purification system

[0026] 11: Engine

[0027] 111: Fuel Injection Section

[0028] 12: Exhaust pipe

[0029] 13: Injection nozzle

[0030] 14: Jar

[0031] 15: Pump

[0032] 16: Purification device

[0033] 17: pipe

[0034] 18: Temperature sensor

[0035] 2: Urea removal device

[0036] 21: Storage Department

[0037] 22: Control Department

[0038] 221: Judgment Department

[0039] 222: Supply Control Department

[0040] 223: Temperature Control Department Detailed Implementation

[0041] <Configuration of Purification System S>

[0042] Figure 1 This is a schematic diagram illustrating the configuration of a purification system S for purifying exhaust gases. The purification system S includes an engine 11, injection nozzles 13, a tank 14, a pump 15, a purification device 16, pipes 17, and a urea removal device 2. For example, the purification system S is installed in a car or on a ship.

[0043] Engine 11 is a diesel engine that burns and expands an air-fuel mixture of fuel and intake gas (air) to generate power. Fuel injection unit 111 injects fuel into the combustion chamber of engine 11 under the control of urea removal device 2. Exhaust gases from engine 11 are discharged to the outside through exhaust pipe 12.

[0044] Purification device 16 purifies the exhaust gas from engine 11. Purification device 16 is a selective catalytic reduction (SCR) denitrification device (so-called urea SCR) installed in the exhaust pipe 12 through which the exhaust gas flows from engine 11. The selective catalytic reduction denitrification device reduces NOx to nitrogen and water by injecting an aqueous urea solution (N) as a precursor of ammonia into the exhaust gas flowing through the exhaust pipe 12.

[0045] Temperature sensor 18 is a sensor unit, including thermocouples or thermistors, that senses the temperature of the exhaust gas flowing into the purification device 16. Temperature sensor 18 is located upstream of the purification device 16 and senses the temperature of the exhaust gas flowing into the purification device 16. The interval at which temperature sensor 18 senses the temperature of the exhaust gas can be appropriately set, for example, set to the length of the processing cycle of the microprocessor of the sensor unit, specifically 100 milliseconds.

[0046] The spray nozzle 13 sprays the urea aqueous solution N into the purification device 16. The urea aqueous solution N is stored in a tank 14. The urea aqueous solution N is supplied from the tank 14 to the spray nozzle 13 through a pipe 17. For example, the pipe 17 is a silicone tube or a rubber tube.

[0047] Pump 15 is a pump that supplies urea aqueous solution N from tank 14 to injection nozzle 13 under the control of urea removal device 2. Additionally, pump 15 can also supply urea aqueous solution from injection nozzle 13 to tank 14 under the control of urea removal device 2. For example, when engine 11 is stopped, pump 15 discharges urea aqueous solution from injection nozzle 13 by supplying urea aqueous solution N from injection nozzle 13 to tank 14.

[0048] Meanwhile, even if the urea aqueous solution N is discharged from the injection nozzle 13, in some cases, the urea aqueous solution N may still remain in the injection nozzle 13. If the urea aqueous solution N remaining in the injection nozzle 13 is heated by high-temperature exhaust gas, residual heat of the exhaust gas, etc., the urea that precipitates due to the evaporation of water from the urea aqueous solution N will undesirably adhere to the inside of the injection nozzle 13. In view of this, when urea adheres to the inside of the injection nozzle 13, the urea removal device 2 raises the temperature of the exhaust gas while the urea aqueous solution N has already been injected into the injection nozzle 13, thereby raising the temperature of the urea aqueous solution N already injected into the injection nozzle 13. As a result, the water solubility of urea increases, making it easier for the urea adhering to the injection nozzle to dissolve in the urea aqueous solution, and thus removing the adhering urea.

[0049] The following describes the configuration of urea removal device 2.

[0050] The urea removal device 2 includes a storage unit 21 and a control unit 22. The storage unit 21 is a storage medium including ROM (read-only memory), RAM (random access memory), hard disk, etc. The storage unit 21 stores the program executed by the control unit 22.

[0051] For example, the control unit 22 is a computing resource that includes a processor such as a CPU (central processing unit). By executing the program stored in the storage unit 21, the control unit 22 performs the functions of a decision unit 221, a supply control unit 222, and a temperature control unit 223.

[0052] The determination unit 221 performs injection control to inject urea aqueous solution N from the injection nozzle 13. Specifically, the determination unit 221 performs injection control to apply a predetermined injection voltage to the injection nozzle 13 and inject the urea aqueous solution N from the injection nozzle 13 into the purification device 16. If urea aqueous solution N is injected from the injection nozzle 13 when the injection voltage is applied, it means that the difference between the maximum and minimum values ​​of the function of the time change of the current value from the time the injection voltage is applied until a predetermined determination time has elapsed is equal to or greater than the determination threshold. On the other hand, if urea aqueous solution N is not injected from the injection nozzle 13 when the injection voltage is applied, it means that the difference between the maximum and minimum values ​​of the function of the time change of the current value is less than the determination threshold.

[0053] The determination unit 221 determines whether urea aqueous solution N is injected from the injection nozzle 13 when injection control is executed. For example, the determination unit 221 executes injection control and simultaneously performs diagnostic control to determine whether the purification device 16 for purifying exhaust gas is operating normally, and determines whether urea aqueous solution N is injected from the injection nozzle 13. Specifically, the determination unit 221 determines whether urea aqueous solution N has been injected based on whether the difference between the maximum and minimum values ​​of a function representing the time change of the current value from the time the injection voltage is applied to the injection nozzle 13 until a determination time has elapsed. If the difference between the maximum and minimum values ​​of the function representing the time change of the current value is equal to or greater than the determination threshold, the determination unit 221 determines that urea aqueous solution N has been injected. If the difference between the maximum and minimum values ​​is less than the determination threshold, the determination unit 221 determines that urea aqueous solution N has not been injected from the injection nozzle 13. Note that the determination unit 221 may determine whether urea aqueous solution N is injected from the injection nozzle 13 by other methods than the above method.

[0054] If it is determined that urea aqueous solution N is not being sprayed from the injection nozzle 13, the supply control unit 222 supplies urea aqueous solution N from the tank 14 to the injection nozzle 13. For example, the supply control unit 222 controls the pump 15 to supply urea aqueous solution N from the tank 14 to the injection nozzle 13. Specifically, the supply control unit 222 performs supply / re-suction control to feed back urea aqueous solution N from the injection nozzle 13 to the tank 14 after supplying urea aqueous solution N from the tank 14 to the injection nozzle 13, and then supplies urea aqueous solution N from the tank 14 to the injection nozzle 13 again. More specifically, the pipe 17 connecting the injection nozzle 13 and the pump 15 is provided with a pipe having a siphon structure. The supply control unit 222 performs multiple supply / re-suction controls to control the liquid level of urea aqueous solution N in the pipe 17, thereby replacing the air trapped in the pipe 17 with urea aqueous solution N and supplying urea aqueous solution N to the injection nozzle 13. When the urea aqueous solution N has been injected into the injection nozzle 13, the urea adhering to the injection nozzle 13 begins to dissolve into the urea aqueous solution N.

[0055] Meanwhile, the water solubility of urea increases with rising water temperature. Figure 2 This is a table showing the relationship between the water solubility of urea and temperature. As the temperature of the urea aqueous solution N injected into the injection nozzle 13 increases, the water solubility of urea increases, thus increasing the likelihood that the urea adhering to the injection nozzle 13 will dissolve into the urea aqueous solution N. In other words, compared to not increasing the temperature of the urea aqueous solution N, increasing the temperature of the urea aqueous solution N injected into the injection nozzle 13 allows the urea adhering to the injection nozzle 13 to dissolve into the urea aqueous solution N in a shorter time.

[0056] Temperature control unit 223 performs control to raise the temperature of the exhaust gas even after the urea aqueous solution N supplied from tank 14 has been injected into the injection nozzle 13. For example, temperature control unit 223 performs control to raise the temperature of the exhaust gas simultaneously with supply control unit 222 starting to control the supply of urea aqueous solution N to the injection nozzle 13. Alternatively, temperature control unit 223 can perform control to raise the temperature of the exhaust gas after a predetermined waiting time has elapsed since the supply control unit 222 begins supply control. The waiting time is the length of time required for the urea aqueous solution N to be injected into the injection nozzle 13 from the start of supply control. Therefore, temperature control unit 223 can begin controlling the temperature of the exhaust gas to rise even after the urea aqueous solution N has been injected into the injection nozzle 13.

[0057] The temperature control unit 223 raises the exhaust gas temperature by continuously controlling heating to perform multiple fuel injections in the combustion chamber of the engine 11 during one combustion cycle. In the heating control of the temperature control unit 223, the exhaust gas temperature is raised by continuously controlling four fuel injections in the combustion chamber during one combustion cycle. Note that the number of fuel injections is not limited to four.

[0058] The temperature control unit 223 raises the temperature of the exhaust gas so that the temperature of the urea aqueous solution N injected into the injection nozzle 13 is equal to or higher than the lower limit temperature of the urea water solubility. For example, the lower limit temperature is set to 80°C when the urea water solubility is [400g / 100ml], and the temperature control unit 223 raises the temperature of the exhaust gas so that the temperature of the urea aqueous solution N injected into the injection nozzle 13 is equal to or higher than 80°C.

[0059] When the engine load is low and the exhaust gas temperature is equal to or lower than the heating temperature, the temperature control unit 223 increases the exhaust gas temperature by continuously heating and controlling the fuel injection multiple times in one combustion cycle. Specifically, by continuously heating and controlling the fuel injection until the exhaust gas temperature is equal to or higher than the heating temperature, the temperature control unit 223 keeps the temperature of the urea aqueous solution N equal to or higher than the lower limit temperature (80°C). The heating temperature is the temperature at which the temperature of the urea aqueous solution N in the injection nozzle 13, heated by the exhaust gas reaching the injection nozzle 13, is equal to or higher than the lower limit temperature (80°C). In other words, the heating temperature is the temperature of the exhaust gas that allows the temperature of the urea aqueous solution N to reach or exceed the lower limit temperature (80°C). When the engine load is high and the exhaust gas temperature is higher than the heating temperature, the temperature control unit 223 performs control to maintain the exhaust gas temperature, keeping the temperature of the urea aqueous solution N at or higher than the lower limit temperature (80°C). For example, the temperature control unit 223 performs control to maintain the exhaust gas temperature by performing fewer fuel injections into the combustion chamber (e.g., once) than the number of injections in the heating control in one combustion cycle.

[0060] Therefore, the exhaust gas, heated to a temperature above the specified temperature, reaches the injection nozzle 13. As a result, the injection nozzle 13 is heated, and the temperature of the urea aqueous solution N injected into the injection nozzle 13 is equal to or higher than the lower limit temperature. Therefore, the urea adhering to the injection nozzle 13 readily dissolves in the urea aqueous solution N. Thus, compared to the case where the urea aqueous solution N is not heated, the adhering urea can be dissolved in the urea aqueous solution N injected into the injection nozzle 13 in a shorter time.

[0061] While performing heating control, the determination unit 221 continues to apply the injection voltage to the injection nozzle 13. Therefore, at the moment when the urea adhering to the injection nozzle 13 dissolves in the urea aqueous solution N, the urea aqueous solution N (in which the adhering urea has already dissolved) is injected from the injection nozzle 13, thereby removing the urea adhering to the inside of the nozzle 13. Since the difference between the maximum and minimum values ​​of the function representing the time change of the current value is equal to or higher than the determination threshold when the urea aqueous solution N is injected from the injection nozzle 13, the determination unit 221 determines that the urea aqueous solution N has been injected. Then, when the determination unit 221 determines that the urea aqueous solution N has been injected, the temperature control unit 223 terminates the heating control. Thus, the temperature control unit 223 can prevent the injection nozzle 13 from being undesirably heated even after the adhering urea has been removed, and from being undesirably heated to a temperature exceeding the heat resistance temperature of the injection nozzle 13.

[0062] Meanwhile, if the temperature of the injection nozzle 13 becomes higher than its heat resistance temperature (e.g., 400°C), the urea adhering material adheres more firmly, causing the injection nozzle 13 to malfunction, its performance to decrease, and so on. Therefore, the temperature control unit 223 performs control to raise the temperature of the exhaust gas, bringing the temperature of the nozzle 13 below the upper limit temperature based on its heat resistance temperature. Specifically, if the exhaust gas temperature is equal to or higher than the upper limit temperature, the temperature control unit 223 stops controlling the temperature rise of the exhaust gas. The upper limit temperature is the temperature at which heat will not cause malfunction or performance degradation of the injection nozzle 13, and is higher than the lower limit temperature. The upper limit temperature is in the range of 250°C to 350°C. Ideally, the upper limit temperature is 280°C. When the exhaust gas temperature equals the upper limit temperature, the temperature of the injection nozzle 13 is lower than its heat resistance temperature and higher than the lower limit temperature. Thus, excessive heating of the injection nozzle 13 is suppressed, and the temperature of the injection nozzle 13 is kept below its heat resistance temperature. Therefore, malfunction and performance degradation of the injection nozzle 13 are suppressed.

[0063] Note that since the urea aqueous solution N has been injected into the injection nozzle 13, the heat required to increase the temperature of the injection nozzle 13 and the urea aqueous solution N increases, thus preventing excessive temperature rise of the injection nozzle 13. Furthermore, to prevent excessive temperature rise of the injection nozzle 13, the temperature control unit 223 can supply coolant for cooling the engine 11 to the injection nozzle 13. In this case, the purification system S includes a pipe for supplying coolant to the injection nozzle 13 and a pump for supplying coolant from the pipe to the injection nozzle 13. When the exhaust gas temperature is equal to or higher than the upper limit temperature, the temperature control unit 223 controls the coolant supply pump to supply coolant to the injection nozzle 13.

[0064] The temperature control unit 223 continuously controls the temperature of the exhaust gas to rise when the exhaust gas temperature is below the upper limit temperature, and stops controlling the temperature rise when the exhaust gas temperature is equal to or higher than the upper limit temperature. Thus, the temperature control unit 223 can keep the temperature of the injection nozzle 13 below the heat resistance temperature, while maintaining the temperature of the urea aqueous solution N above the lower limit temperature (80°C).

[0065] Figure 3 This is a schematic diagram illustrating the control measures used to raise the temperature of exhaust gases. Figure 3 In the diagram, the horizontal axis represents time, and the vertical axis represents temperature. The exhaust gas temperature G1 is a curve representing the temperature change of the exhaust gas flowing into the purification device 16. The urea solution temperature G2 is a curve representing the temperature change of the urea solution N that has been injected into the injection nozzle 13.

[0066] Time T1 is the time for performing temperature control. The temperature control unit 223 raises the temperature of the exhaust gas so that the temperature of the urea aqueous solution N injected into the injection nozzle 13 is equal to or higher than the lower limit temperature A. Specifically, the temperature control unit 223 raises the temperature of the exhaust gas so that the exhaust gas temperature G1 is equal to or higher than the heating temperature B. Thus, the temperature control unit 223 can make the temperature of the injection nozzle 13 equal to or higher than the lower limit temperature A.

[0067] Furthermore, the temperature control unit 223 controls the temperature of the exhaust gas to keep it below the upper limit temperature C. Specifically, when the temperature of the exhaust gas exceeds the upper limit temperature C, the temperature control unit 223 stops controlling the temperature rise of the exhaust gas. As a result, the temperature control unit 223 can keep the temperature of the injection nozzle 13 below a temperature D lower than the heat resistance temperature, thereby suppressing malfunctions and performance degradation of the injection nozzle 13.

[0068] <Urea removal process performed by urea removal device 2>

[0069] Figure 4 This is a flowchart illustrating an example of a urea removal process. The urea removal process is part of a diagnostic control that determines whether the purification device 16 and the injection nozzle 13 are operating normally. For example, the urea removal process is executed at the moment when the diagnostic control begins to determine whether the purification device 16 and the injection nozzle 13 are operating normally.

[0070] The determination unit 221 performs control to spray urea aqueous solution N from the injection nozzle 13 (step S1). Specifically, in order to spray urea aqueous solution N from the injection nozzle 13, the determination unit 221 applies an injection voltage to the injection nozzle 13.

[0071] The determination unit 221 determines whether the urea aqueous solution N is injected from the injection nozzle 13 (step S2). For example, the determination unit 221 determines whether the urea aqueous solution N is injected from the injection nozzle 13 based on whether the difference between the maximum and minimum values ​​of a function representing the time change of the current value from the application of the injection voltage until the determination time has elapsed. If the difference between the maximum and minimum values ​​of the function is equal to or greater than the determination threshold (yes in step S2), the determination unit 221 determines that the urea aqueous solution N is injected from the injection nozzle 13 and ends the process.

[0072] If it is determined that the urea aqueous solution N is not being sprayed from the injection nozzle 13 (no in step S2), the supply control unit 222 supplies the urea aqueous solution N to the injection nozzle 13 (step S3). Specifically, the supply control unit 222 controls the pump 15 to repeatedly supply / re-suction, thereby controlling the liquid level of the urea aqueous solution N in the pipe 17 (which includes a pipe with a siphon structure). As a result, the air remaining in the pipe 17 is replaced by the urea aqueous solution N, and the urea aqueous solution N is supplied from the tank 14 to the injection nozzle 13.

[0073] When the urea aqueous solution N supplied from tank 14 is supplied to the injection nozzle 13, and the urea aqueous solution N has been injected into the injection nozzle 13, the temperature control unit 223 determines whether the temperature of the exhaust gas is lower than the heating temperature B (step S4). If the temperature of the exhaust gas is lower than the heating temperature B (yes in step S4), the temperature control unit 223 performs control to raise the temperature of the exhaust gas (step S5). Specifically, when a waiting time has elapsed since the supply control unit 222 started supplying the urea aqueous solution N to the injection nozzle 13, the temperature control unit 223 starts heating control to perform four fuel injections into the combustion chamber in one combustion cycle, and raises the temperature of the exhaust gas.

[0074] If the exhaust gas temperature is equal to or higher than the heating temperature B (step S4 is not specified), the temperature control unit 223 determines whether the exhaust gas temperature is equal to or higher than the upper limit temperature C (step S6). If the exhaust gas temperature is equal to or higher than the upper limit temperature C (step S6 is specified), the temperature control unit 223 performs control to lower the exhaust gas temperature (step S7). For example, if heating control is being implemented, the temperature control unit 223 stops the heating control. Furthermore, the temperature control unit 223 supplies coolant from the engine 11 to the injection nozzle 13.

[0075] If the temperature of the exhaust gas is lower than the upper limit temperature C (no in step S6), the temperature control unit 223 returns to step S4. The urea removal device 2 repeats steps S4 to S7 during the execution of diagnostic control.

[0076] While performing heating control, the determination unit 221 continues to apply the injection voltage to the injection nozzle 13. If the difference between the maximum and minimum values ​​of the function representing the time change of the current value is equal to or greater than the determination threshold, the determination unit 221 determines that urea aqueous solution N has been injected. When the determination unit 221 determines that urea aqueous solution N has been injected, the temperature control unit 223 terminates the heating control.

[0077] If the difference between the maximum and minimum values ​​of the function representing the time-varying current value is less than a determination threshold, the determination unit 221 determines that no urea aqueous solution N has been injected. When the determination unit 221 determines that no urea aqueous solution N has been injected, the temperature control unit 223 continues heating control. Even after a predetermined diagnostic time has elapsed since the start of diagnostic control, if the difference between the maximum and minimum values ​​of the function representing the time-varying current value is still less than the determination threshold, the determination unit 221 determines that the injection nozzle 13 is abnormal. The diagnostic time can be appropriately set according to the specifications of the vehicle equipped with the purification system S, for example, set to 1500 seconds.

[0078] <Advantages of Urea Removal Device 2>

[0079] As described above, the urea removal device 2 controls the temperature of the exhaust gas to rise while the urea aqueous solution N has already been injected into the injection nozzle 13. As a result, the heated exhaust gas reaches the injection nozzle 13, further raising the temperature of the urea aqueous solution N already injected into the nozzle 13, thus increasing the solubility of the urea aqueous solution N. Consequently, the urea adhering to the injection nozzle 13 dissolves more readily into the urea aqueous solution N in a shorter time, effectively removing the urea adhering to the injection nozzle 13.

[0080] Furthermore, since the urea aqueous solution N has already been injected into the injection nozzle 13, the temperature of the injection nozzle 13 is unlikely to rise even if the temperature of the exhaust gas increases. Therefore, the undesirable rise of the temperature of the injection nozzle 13 to above its heat resistance temperature is prevented, and correspondingly, malfunctions and performance degradation of the injection nozzle 13 can be suppressed.

[0081] Although the invention has been described using embodiments, the technical scope of the invention is not limited to the scope described in the above embodiments, and various modifications and alterations can be made within the scope of the spirit of the invention. For example, in the above embodiments, the temperature control unit 223 is part of the urea removal device 2, but it is not limited thereto. An engine control device that mainly controls engine power / exhaust gas temperature through engine fuel injection may also be installed as a temperature control unit 223 separate from the urea removal device 2, and coordinated control may be performed together with the urea removal device 2 using CAN (Controller Area Network) communication or the like. Furthermore, all or part of the devices may be configured in any unit in a distributed / integrated manner, either functionally or physically. In addition, embodiments of the invention include new embodiments resulting from combining any one of the multiple embodiments. The advantages of the new embodiments resulting from the combination combine the advantages of the original embodiments.

Claims

1. A urea removal device comprising: a determination section that determines whether or not urea water solution is being injected from an injection nozzle when control is being executed to inject the urea water solution from the injection nozzle into an exhaust pipe through which exhaust gas of an engine is flowing; a supply control section that controls a pump that supplies the urea water solution from a tank that stores the urea water solution to the injection nozzle, and causes the urea water solution to be supplied from the tank to the injection nozzle in the case where it is determined that the urea water solution is not being injected from the injection nozzle; a temperature control section that, in a state in which urea water solution that is being supplied from the tank has been injected into the injection nozzle, executes control to raise the temperature of exhaust gas, the temperature control section ending the control to raise the temperature of exhaust gas when the determination section determines that the urea water solution is being injected from the injection nozzle after starting the control to raise the temperature of exhaust gas. the temperature control section executing the control to raise the temperature of exhaust gas so that the temperature of the urea water solution that has been injected into the injection nozzle is equal to or higher than a lower limit temperature that is a temperature at which the aqueous solubility of urea becomes a predetermined solubility.

2. The urea removal device of claim 1, wherein, the temperature control section executing the control to raise the temperature of exhaust gas so that the temperature of the urea water solution that has been injected into the injection nozzle is equal to or higher than the lower limit temperature, and additionally so that the temperature of the injection nozzle is lower than an upper limit temperature that is based on the heat resistance temperature of the injection nozzle, the upper limit temperature being higher than the lower limit temperature.

3. The urea removal device of claim 2, wherein, the temperature control section raising the temperature of the exhaust gas by continuously controlling so that a fuel injection section, which is used to inject fuel into a combustion chamber of the engine, performs multiple fuel injections in one combustion cycle of the engine for a predetermined period of time.

4. The urea removal device according to any one of claims 1 to 3, wherein, the supply control section executing the control to supply the urea water solution to the injection nozzle while implementing diagnostic control to determine whether or not a purification device that purifies the exhaust gas is operating normally.

5. The urea removal device according to any one of claims 1 to 3, wherein, the determination section can determine that the urea water solution is being injected from the injection nozzle in the case where the difference between a maximum value and a minimum value of a function that represents the temporal change in the current value from when the injection voltage is applied to the injection nozzle until a determination time elapses is equal to or greater than a determination threshold value, and determine that the urea water solution is not being injected from the injection nozzle in the case where the difference is less than the determination threshold value, when injection control is being executed to inject the urea water solution into the injection nozzle by applying the injection voltage to the injection nozzle.

6. The urea removal device of any one of claims 1 to 3, wherein, the determination section determines that the urea water solution is being injected from the injection nozzle in the case where the injection voltage is applied to the injection nozzle after starting the control to raise the temperature of exhaust gas, and the difference observed when the injection voltage is being applied is equal to or greater than the determination threshold value.

7. The urea removal device of claim 6, wherein, 8. The urea removal device according to claim 7, wherein the determination section continues to apply the injection voltage to the injection nozzle after starting the control to raise the temperature of exhaust gas. ​ 9. The urea removal device of any one of claims 1 to 3, wherein, The temperature control section starts the control to raise the temperature of the exhaust gas when a waiting time required for the urea aqueous solution to be injected into the injection nozzle elapses from a start time point of the control of the supply of the urea aqueous solution to the injection nozzle.

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