JP4978635B2 - Control device for exhaust purification system - Google Patents

Description

  The present invention relates to a control device for an exhaust purification system, and in particular, an exhaust purification system employing a selective reduction catalyst (SCR) that selectively purifies nitrogen oxides (NOx) in exhaust by ammonia as a reducing agent. This relates to the control device.

  In recent years, urea SCR systems have been developed as exhaust gas purification systems for purifying NOx in exhaust gas at a high purification rate in engines (particularly diesel engines) applied to automobiles and the like, and some have been put into practical use. The following configuration is known as a urea SCR system.

  That is, a selective reduction type NOx catalyst is provided in an exhaust pipe connected to the engine body, and a urea water addition valve for adding urea water (reducing agent solution) as a NOx reducing agent is provided upstream of the exhaust. Yes. The urea water is stored in the tank, and is fed from the tank to the urea water addition valve by a pump disposed in a urea water pipe connecting the tank and the urea water addition valve. In this system, urea water in the tank is added into the exhaust pipe from the urea water addition valve, so that ammonia (NH3) generated by hydrolysis of urea water reacts with NOx in the exhaust gas on the NOx catalyst. NOx in the exhaust is selectively reduced and purified.

  In the above system, urea water having the lowest freezing temperature (32.5%) is used. For example, urea water having a urea concentration of 32.5% is frozen at minus 11 ° C. However, in an environment where the temperature is extremely low, such as in a cold region or a severe cold season, the urea water in the tank may be frozen.

  Therefore, in the urea water SCR system, it is possible to prevent the urea water from freezing by providing a heater in the tank or circulating the engine cooling water, and to thaw the frozen urea water at the time of freezing the urea water. (For example, refer to Patent Document 1). In Patent Document 1, a heater is provided in the tank, and the heater is operated when the temperature of the tank wall surface is equal to or lower than a predetermined temperature (for example, a temperature slightly higher than the freezing temperature of urea water). Further, the operation of the heater is stopped when the urea water temperature becomes higher than a predetermined temperature by the heating by the heater. As a result, the thawing of the urea water is performed quickly, and it becomes possible to add the urea water into the exhaust gas from the urea water addition valve.

JP 2005-282413 A

  Under the situation where the urea water is frozen, when the urea water temperature reaches the melting point with the supply of heat from a heater or the like, the urea water is gradually thawed from a position close to the heat source. At this time, when the urea water addition into the exhaust pipe is started at the time when thawing of the urea water in the tank starts (for example, when it is determined that the urea water temperature has reached the melting point based on the measured value of the temperature sensor). Then, a sufficient amount of urea water in the liquid state is not secured in the tank, and the urea water addition control is performed in a state where the urea water cannot be sufficiently supplied into the exhaust pipe. In such a case, it is conceivable that urea water in an amount corresponding to the required amount is not actually supplied into the exhaust pipe despite the addition control being performed.

  The present invention has been made to solve the above problems, and provides an exhaust purification system control device capable of sufficiently supplying a reducing agent solution in a reducing agent tank from the inside of the tank to a reducing agent addition device. The main purpose is to do.

  The present invention employs the following means in order to solve the above problems.

The invention described in claim 1 is a reducing agent tank that stores a reducing agent solution having a predetermined concentration, and a selective reduction catalyst that is provided in an exhaust passage of an internal combustion engine and selectively purifies NOx in exhaust gas by the reducing agent solution. And a heating means for heating the reducing agent solution in the reducing agent tank, and is applied to an exhaust gas purification system in which the reducing agent solution is added by a reducing agent addition device to the exhaust upstream side of the selective reduction catalyst, When the reducing agent solution is heated and thawed by the heating means, the reduction around the reducing agent suction port is based on the temperature distribution in the surrounding tank around the reducing agent suction port arranged in the reducing agent tank. The thawing determination means for determining the thawing state of the reducing agent solution, and the reducing agent adding device based on the thawing state of the reducing agent solution around the reducing agent suction port determined by the thawing determination means. And addition control means for performing an addition control of the reducing agent solution,
It is characterized by providing.

  In cold regions, when the temperature falls at night or the like, the reducing agent solution stored in the reducing agent tank may freeze. Therefore, when the reducing agent solution is frozen, the frozen reducing agent solution is thawed by a heating means such as a heater. However, in the piping connecting the reducing agent tank and the reducing agent addition device, the reducing agent solution in the thawed state is insufficient near the reducing agent solution inlet (reducing agent inlet) disposed in the tank. In this case, it is conceivable that an amount of the reducing agent solution corresponding to the required amount is not actually added to the exhaust passage even though the addition control of the reducing agent solution is performed.

  In this regard, in the present invention, when the reducing agent solution is frozen by the heating means when the reducing agent solution is frozen, the temperature distribution (temperature gradient) around the reducing agent suction port in the reducing agent tank is set. Based on the determination result, the thawing state of the reducing agent solution around the reducing agent suction port is determined, and the addition of the reducing agent solution is controlled based on the determination result. Therefore, the reducing agent that has accumulated around the reducing agent suction port. Addition control of the reducing agent solution can be performed according to the amount of the solution. Therefore, according to the present invention, the reducing agent solution in the reducing agent tank can be sufficiently supplied from the inside of the tank to the reducing agent adding device.

  When the reducing agent solution is thawed by the heating unit, the reducing agent solution in the vicinity of the heating unit is thawed in order. That is, in the thawing implementation period of the reducing agent solution, the vicinity of the heating means becomes a liquid phase, and the portion away from the heating means becomes a solid phase. Moreover, it is thought that the liquid phase part in a reducing agent tank expands in the direction away from a heating means as the thawing implementation time by a heating means passes. Therefore, when the heating means is provided in the vicinity of the reducing agent suction port, the reducing agent solution is thawed in order from the periphery of the reducing agent suction port.

  In view of this, the invention according to claim 2 is characterized in that the heating means is provided in the vicinity of the reducing agent suction port, and the thawing determination means is equivalent to the melting point of the reducing agent solution based on the temperature distribution. The temperature position is estimated, and the thawing state of the reducing agent solution around the reducing agent suction port is determined based on the distance from the reducing agent suction port at the same position. According to this configuration, paying attention to the fact that the reducing agent solution is thawed in order from the periphery of the reducing agent suction port, the melting point of the reducing agent solution is obtained based on the temperature distribution around the reducing agent suction port. Estimate the position. The position of the boundary point between the liquid phase and the solid phase is estimated by calculating the distance from the reducing agent suction port at the same position. Therefore, the liquid amount of the reducing agent solution existing around the reducing agent suction port can be detected based on the position of the boundary point (distance from the reducing agent suction port).

  Here, as the addition control of the reducing agent solution based on the distance from the reducing agent suction port, for example, the addition of the reducing agent solution may be started when the distance reaches a determination value. Or you may restrict | limit the addition amount of a reducing agent solution according to the distance from a reducing agent inlet.

  In the reducing agent solution in the reducing agent tank, the temperature (hereinafter also referred to as reducing agent temperature) varies depending on the separation distance from the heating means, and the reducing agent temperature decreases as the separation distance increases. For this reason, it is considered that the reducing agent temperature also changes around the reducing agent suction port according to the distance from the heating means. In view of this point, the invention according to claim 3 is characterized in that the reducing agent temperature measuring means for measuring the temperature of the reducing agent solution at a plurality of measurement points at different distances from the reducing agent suction port, and the reducing agent temperature. Temperature distribution estimation means for estimating the temperature distribution in the tank based on temperature measurement values at each measurement point by the measurement means, and the temperature distribution in the tank estimated by the temperature distribution estimation means Based on the above, the thawing state of the reducing agent solution around the reducing agent inlet is determined. According to this configuration, the temperature distribution around the reducing agent inlet can be estimated by measuring the reducing agent temperature at at least two points.

  In consideration of the fact that the reducing agent temperature varies depending on the distance from the heating unit, it is desirable that each measurement point of the temperature measuring unit and the reducing agent suction port are arranged on the same straight line. The measurement points may be determined at least in the vicinity of the reducing agent suction port and at a position away from the reducing agent suction port.

  When the outer periphery of the reducing agent tank is in contact with the outside air, the reducing agent temperature in the vicinity of the inner wall of the tank is considered to be equal to the outside air temperature. In view of this point, the invention according to claim 4 is directed to a reducing agent temperature measuring unit that measures the temperature of the reducing agent solution at a predetermined measurement point, an outside air temperature measuring unit that measures an outside air temperature, and the reducing agent temperature. Temperature distribution estimation means for estimating the temperature distribution in the tank based on the temperature measurement value at the measurement point by the measurement means and the outside air temperature measurement value by the outside air temperature measurement means, and the thawing determination means, Based on the temperature distribution in the tank estimated by the temperature distribution estimating means, the thawing state of the reducing agent solution around the reducing agent suction port is determined. According to this configuration, the temperature distribution around the reducing agent inlet can be estimated by measuring the reducing agent temperature at at least one point and by measuring the outside air temperature.

  The invention according to claim 5 is a reducing agent temperature measuring means for measuring the temperature of the reducing agent solution at a predetermined measurement point, and a reducing agent for estimating the temperature of the reducing agent solution at or near the reducing agent inlet. The temperature distribution in the tank based on the temperature estimation value at the measurement point by the temperature estimation means, the reducing agent temperature measurement means, and the temperature estimation value at or near the reducing agent suction port by the reducing agent temperature estimation means A temperature distribution estimating means for estimating the defrosting state of the reducing agent solution around the reducing agent suction port based on the temperature distribution in the tank estimated by the temperature distribution estimating means. Determine. According to this configuration, since the estimated value is used as the reducing agent temperature at or near the reducing agent inlet, the temperature distribution around the reducing agent inlet is estimated by measuring the reducing agent temperature at at least one point. Can do. Here, the estimation of the reducing agent temperature at or near the reducing agent suction port is performed, for example, based on the amount of heat generated by the heating unit provided in the vicinity of the reducing agent suction port.

  In the invention described in claim 6, the heating means is an electric heater. By using an electric heater as the heating means, temperature fluctuations can be reduced at the base of temperature distribution formation. At this time, it is preferable that an electric heater is disposed in the vicinity of the reducing agent suction port to heat the reducing agent solution in the vicinity of the reducing agent suction port. Thereby, the reducing agent suction port can be used as a base point for forming the temperature distribution, and the temperature distribution around the reducing agent suction port can be estimated appropriately.

The block diagram which shows the outline | summary of a urea SCR system. The flowchart which shows the process sequence of a urea water addition process. The temperature gradient figure in the circumference | surroundings of a reducing agent suction inlet. The temperature gradient figure in the circumference | surroundings of the reducing agent suction inlet in other embodiment. The temperature gradient figure in the circumference | surroundings of the reducing agent suction inlet in other embodiment. The figure which shows the relationship between the thawing distance LN and the correction coefficient K.

  Hereinafter, an embodiment of an exhaust gas purification system embodying the present invention will be described with reference to the drawings. The exhaust purification system of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as a urea SCR system. First, the configuration of this system will be described in detail with reference to FIG. FIG. 1 is a configuration diagram showing an outline of a urea SCR system according to the present embodiment. This system has various actuators and various sensors for purifying exhaust, and ECU (Electronic Control Unit) 40, etc., for purifying exhaust discharged by a diesel engine (not shown) mounted on an automobile. Has been built.

  In the engine exhaust system of FIG. 1, an exhaust pipe 11 connected to the engine body and forming an exhaust passage is provided. In the exhaust pipe 11, a DPF (Diesel Particulate Filter) 12, a selective catalytic reduction catalyst in order from the exhaust upstream side. (Hereinafter referred to as SCR catalyst) 13 is provided. Further, a urea water addition valve 15 for adding and supplying urea water (urea aqueous solution) as a reducing agent solution into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11.

  In the exhaust pipe 11, on the downstream side of the SCR catalyst 13, there is provided an exhaust sensor 16 in which a NOx detector (NOx sensor) and an exhaust temperature detector (exhaust temperature sensor) are both built. The exhaust sensor 16 detects the amount of NOx in the exhaust (NOx purification rate by the SCR catalyst 13) and the temperature of the exhaust on the downstream side of the SCR catalyst 13.

  An oxidation catalyst 19 as an ammonia removing device is provided further downstream of the SCR catalyst 13 in the exhaust pipe 11. The oxidation catalyst 19 removes ammonia (NH3) discharged from the SCR catalyst 13, that is, excess ammonia.

  Next, the configuration of each of the above parts constituting the system will be described.

  The DPF 12 is a PM removal filter that collects PM (particulate matter) in the exhaust gas. The DPF 12 carries a platinum-based oxidation catalyst and removes HC and CO together with a soluble organic component (SOF) that is one of the PM components. The PM collected in the DPF 12 can be removed by combustion by post-injection after the main fuel injection in the diesel engine or the like (corresponding to a regeneration process), and thus the DPF 12 can be used continuously.

The SCR catalyst 13 promotes a NOx reduction reaction (exhaust purification reaction).
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 12H2O (Formula 2)
NO + NO2 + 2NH3 → 2N2 + 3H2O (Formula 3)
Such a reaction is promoted to reduce NOx in the exhaust gas. A urea water addition valve 15 provided on the upstream side of the SCR catalyst 13 is additionally supplied with ammonia (NH 3) as a NOx reducing agent in these reactions.

  The urea water addition valve 15 has substantially the same configuration as an existing fuel injection valve (injector), and since a known configuration can be adopted, the configuration will be briefly described here. The urea water addition valve 15 is configured as an electromagnetic on-off valve provided with a drive unit composed of an electromagnetic solenoid or the like, and a valve body unit having a urea water passage through which urea water flows and a needle for opening and closing the tip jet port 15a. The valve is opened or closed based on a drive signal from the ECU 40. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and urea water is added (injected) from the tip ejection port 15a as the needle moves.

  Urea water is sequentially supplied from the urea water tank 21 to the urea water addition valve 15. Hereinafter, the configuration of the urea water supply system will be described. In the following description, for the sake of convenience, the urea water tank 21 side is on the upstream side and the urea water addition valve 15 side is on the downstream, based on the case where urea water is supplied from the urea water tank 21 to the urea water addition valve 15. List as side.

  The urea water tank 21 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration CNH is stored therein. In this embodiment, the urea concentration is 32.5%, which is the concentration at which the freezing temperature (freezing point) is the lowest. When the urea concentration is 32.5%, it freezes at minus 11 ° C. or lower.

  The urea water tank 21 and the urea water addition valve 15 are connected by a urea water supply pipe 22, and a urea water passage (reducing agent passage) is formed in the urea water supply pipe 22. A urea water inlet 24 for sucking urea water is formed at the tip of the urea water supply pipe 22 on the urea water tank 21 side, and urea water is stored in the urea water tank 21 in the state where urea water is stored. The water inlet 24 is immersed in urea water.

  A urea water pump 23 is provided in the middle of the urea water supply pipe 22. The urea water pump 23 is an in-line electric pump that is rotationally driven by a drive signal from the ECU 40. In this embodiment, the urea water pump 23 is provided outside the urea water tank 21, that is, in a state where it is not immersed in the urea water. Thereby, damage to the urea water pump 23 due to freezing and expansion of the urea water in the urea water tank 21 is suppressed.

  In the present embodiment, the urea water pump 23 can rotate in either the forward or reverse direction. The urea water in the urea water tank 21 is sucked up by the normal rotation of the urea water pump 23, and the urea water is sucked back into the urea water tank 21 by the reverse rotation of the urea water pump 23.

  In the urea water supply pipe 22, a filter device 25 for filtering urea water is provided upstream of the urea water pump 23 (on the urea water tank 21 side). Further, a pressure adjusting valve 26 for adjusting the pressure of the urea water is provided on the downstream side (the urea water addition valve 15 side) from the urea water pump 23.

  At the time of urea water pressure feeding to the urea water addition valve 15 side, the urea water pump 23 is rotationally driven in the normal rotation direction by energizing the urea water pump 23. As a result, the urea water in the urea water tank 21 is pumped up and flows downstream through the filter device 25. At this time, foreign substances contained in the urea water are removed by the filter device 25. Then, urea water is discharged (pressure fed) from the urea water pump 23, the urea water is adjusted to a predetermined supply pressure by the pressure regulating valve 26, and then fed to the urea water addition valve 15. Further, the excess urea water as a result of the pressure adjustment is returned to the urea water tank 21 through the return pipe 27.

  When the urea water is sucked back into the urea water tank 21, the urea water pump 23 is driven to rotate in the reverse rotation direction. As a result, the urea water in the urea water supply pipe 22 is sucked back and flows into the urea water tank 21. In the present embodiment, this urea water sucking back operation is performed by the ECU 40 when the engine is stopped. That is, it is avoided that the urea water remains in the urea water supply pipe 22 while the vehicle is left after the engine is stopped, thereby preventing the urea water supply pipe 22 from being damaged due to freezing and expansion of the urea water.

  A heating element 28 is provided in the urea water tank 21. In the present embodiment, the heating element 28 is configured as an electric heater that performs heating in response to a drive signal from the ECU 40, and heats the urea water inlet 24 and its vicinity by energization. Thereby, when the heating element 28 is energized, the urea water is gradually thawed from a position close to the heating element 28, that is, from the vicinity of the urea water inlet 24. As shown in FIG. 1, the heating element 28 may be disposed in the vicinity of the urea water inlet 24, or may be incorporated in the urea water inlet 24 in the urea water supply pipe 22. In FIG. 1, reference numeral 28 a is a driver for driving the heating element 28.

  A urea water temperature sensor 31 for measuring the urea water temperature TN stored in the urea water tank 21 is provided in the urea water tank 21. In this embodiment, the urea water temperature sensor 31 is located near the urea water suction port 24 and at a distance from the urea water suction port 24 by the distance L1 and the distance from the urea water suction port 24. And a second sensor 31b having a measurement point at a position separated by L2 (L2> L1). The second sensor 31b is provided on a straight line connecting the urea water inlet 24 and the first sensor 31a. A urea water pressure sensor 32 that detects the pressure of the urea water in the urea water supply pipe 22 (line pressure PNH) is provided in the middle of the urea water supply pipe 22.

  In the system, the ECU 40 is a part that mainly performs control related to exhaust gas purification as an electronic control unit. The ECU 40 includes a known microcomputer (not shown), and performs various controls related to exhaust purification by operating various actuators such as the urea water addition valve 15 in a desired manner based on detection values of various sensors. carry out. Specifically, for example, detection signals are input from various sensors such as the exhaust sensor 16, the urea water temperature sensor 31, and the urea water pressure sensor 32 described above, and the energization time of the urea water addition valve 15 and the heating element 28 are based on the detection signals. The heating timing by the control, the driving amount of the urea water pump 23, and the like are controlled. Thereby, an appropriate amount of urea water is added and supplied into the exhaust pipe 11 at an appropriate time.

  In this embodiment, as the heating control of the urea water by the heating element 28, in any one of the urea water temperature sensors 31 (the first sensor 31a and the second sensor 31b), the urea water temperature TN has the melting point TM of the urea water at the specified concentration CNH. (It is minus 11 degrees C in this embodiment) When it is detected that it is below, it supplies with electricity to the heat generating body 28, and implements the heating of urea water. Further, when the urea water temperature TN detected by the urea water temperature sensor 31 during the heating by the heating element 28 becomes equal to or higher than a predetermined temperature higher than the melting point TM, the energization of the heating element 28 is stopped and the urea water is heated. Stop.

In the above system, during operation of the engine, the urea water in the urea water tank 21 is pumped to the urea water addition valve 15 through the urea water supply pipe 22 by driving the urea water pump 23, and the urea water addition valve 15 in the exhaust pipe 11 is driven. The urea water is added and supplied. Then, urea water is supplied to the SCR catalyst 13 in the exhaust pipe 11 together with the exhaust gas, and the exhaust gas is purified by the NOx reduction reaction in the SCR catalyst 13. When reducing NOx, for example,
(NH2) 2CO + H2O → 2NH3 + CO2 (Formula 4)
As a result, urea water is hydrolyzed at a high temperature due to exhaust heat. As a result, ammonia (NH 3) is generated and adsorbed on the SCR catalyst 13, and NOx in the exhaust gas is selectively reduced and removed by the ammonia in the SCR catalyst 13. That is, NOx is reduced and purified by performing a reduction reaction based on ammonia (the above reaction formulas (Formula 1) to (Formula 3)) on the SCR catalyst 13.

  By the way, in an automobile used in a cold region, for example, when the outside air temperature at the next engine start is extremely low (for example, minus 10 ° C. or less) after the engine is stopped, urea water in the urea water tank 21 is used. May freeze. In this case, the ECU 40 operates the heating element 28 to defrost urea water. However, there is a temperature difference between the vicinity of the heating element 28 and the position away from the heating element 28 due to the difference in distance from the heating element 28, and therefore, when thawing by the heating element 28, solid phase is used in the urea water in the urea water tank 21. It is conceivable that a part and a liquid phase part are formed.

  That is, as the heating by the heating element 28 proceeds, the liquid phase gradually changes from the vicinity of the heating element 28 to the solid phase. At this time, if a sufficient amount of urea water is not thawed around the urea water suction port 24, the amount of urea water that can be sucked from the urea water suction port 24 is insufficient when the urea water pump 23 is operated. In such a case, a sufficient amount of urea water cannot be supplied to the urea water addition valve 15 in spite of performing urea water addition control. For this reason, it is conceivable that an amount of urea water corresponding to the control amount calculated as the amount to be added to the exhaust passage cannot be supplied into the exhaust pipe 11.

  Therefore, in the present embodiment, when the urea water is frozen, the thawing state of the urea water around the urea water suction port 24 is determined based on the temperature gradient around the urea water suction port 24, and the determination Based on the result, urea water is added into the exhaust pipe 11. Specifically, the temperature gradient between the urea water inlet 24 and its surroundings in the urea water tank 21 is estimated based on two measured temperatures by the urea water temperature sensor 31. Then, by using the same temperature gradient, the point (boundary point PM) where the urea water temperature is minus 11 ° C. in the urea water tank 21 is specified, and the distance from the urea water inlet 24 to the boundary point PM ( The thawing distance LM) is calculated. When the thawing distance LM is larger than the determination value Lα, the operation of the urea water pump 23 is permitted. In other words, the boundary point between the frozen part and the thawed part in the urea water tank 21 is specified, and based on the distance from the urea water suction port 24 at the boundary point, the area around the urea water suction port 24 is sufficient. Addition of urea water is started on the condition that it is determined that there is an amount of urea water (liquid).

  FIG. 2 is a flowchart showing a processing procedure of processing related to urea water addition control (urea water addition processing). This process is repeatedly executed by the ECU 40 at a predetermined time period.

  In FIG. 2, in step S11, it is first determined whether or not the engine has been started. The engine start determination is performed, for example, by determining that the ignition switch is ON or that the engine speed is not zero. If the engine has been started, the process proceeds to step S12 to determine whether or not the addition of urea water is permitted. If the addition of urea water has not been permitted yet, the process proceeds to step S13.

  In step S13, the urea water temperature in the vicinity of the urea water suction port 24 (suction port temperature Ta) is measured by the first sensor 31a, and the urea water temperature at a position relatively far from the urea water suction port 24 by the second sensor 31b. (Tank temperature Tb) is measured. That is, the suction port temperature Ta is the urea water temperature at a position away from the urea water suction port 24 by a distance L1, and the in-tank temperature Tb is the urea water temperature at a position away from the urea water suction port 24 by a distance L2. is there.

  In the subsequent step S14, based on the suction port temperature Ta and the tank internal temperature Tb, a temperature gradient between the two points (temperature gradient around the urea water suction port 24) is estimated, and the thawing distance LM is calculated from the temperature gradient. To do. In estimating the temperature gradient, in the present embodiment, in view of the fact that the urea water temperature at that position is estimated according to the distance from the heating element 28, the larger the distance is, the greater the distance from the urea water inlet 24 is. The temperature distribution in the urea water tank 21 is determined on the assumption that the urea water temperature is low as the value increases.

  FIG. 3 is a temperature distribution diagram around the urea water inlet 24 when the frozen urea water transitions from the solid state to the liquid state. The distance L from the urea water inlet 24 and the urea water temperature TN are shown in FIG. Showing the relationship. In FIG. 3, it is assumed that the outside air temperature is extremely low (for example, about −20 ° C.) when the engine is started for an automobile used in a cold region.

  In FIG. 3, the distance from the urea water inlet 24 is determined by setting the urea water temperature TN between L1 (point A in the figure) and L2 (point B in the figure), so that the urea water inlet 24 is at the center. The ambient temperature distribution is estimated. In this embodiment, the urea water temperature TN between the distance L1 and L2 from the urea water suction port 24 is determined by a linear function, and the separation distance from the heating element 28 (the separation distance from the urea water suction port 24). ) Increases, the urea water temperature NT at that position decreases. The thawing distance LM is calculated as a value (point C in FIG. 3) on the straight line connecting the points A and B and when the urea water temperature TN is minus 11 ° C.

  The method for determining the urea water temperature TN between A and B is not limited to the method using a linear function, and may be a method using a multidimensional function. In addition, the thawing distance LM is calculated using, for example, a mathematical formula represented by the following formula (5). Specifically, in the relationship between the distance L in FIG. 3 and the urea water temperature TN, the slope S1 of the straight line connecting these points from the coordinates of the points A (L1, Ta) and the coordinates of the points B (L2, Tb). Ask for. By using this slope S1, the distance L at the urea water temperature TN = −11 ° C. is calculated, and this is set as the thawing distance LM.

LM = (-11-Tb) / S1 + L2 (Formula 5)
However, S1 = (Tb−Ta) / (L2−L1)

  Returning to the description of FIG. 2, in step S15, it is determined whether or not the calculated thawing distance LM is larger than the determination value Lα. In this embodiment, since urea water is sucked back when the engine is stopped, the determination value Lα is set in advance in consideration of the need to fill the urea water supply pipe 22 with urea water when the engine is started. is there.

  In the present embodiment, the temperature measurement points of the first sensor 31a and the second sensor 31b are determined so that the determination value Lα exists between the distance L1 and the distance L2.

  When the thawing distance LM is equal to or less than the determination value Lα, the urea water suction port 24 is not sufficiently secured around the urea water suction port 24, and therefore the addition of urea water into the exhaust pipe 11 is prohibited. On the other hand, when the thawing distance LM is larger than the determination value Lα, addition of urea water into the exhaust pipe 11 is permitted. Thereby, when there is a request to add and supply urea water into the exhaust pipe 11 from the urea water addition valve 15, the urea water pump 23 is driven, and the urea water is added into the exhaust pipe 11. Become.

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

  When the urea water is frozen, the thawing state of the urea water around the urea water inlet 24 is determined based on the temperature gradient around the urea water inlet 24 arranged in the urea water tank 21; Since the urea water is added to the exhaust pipe 11 based on the determination result, the urea water is added according to the amount of urea water accumulated around the urea water suction port 24 in the urea water addition control. Water addition can be performed. Thereby, urea water addition can be started in a state where a sufficient amount of urea water is secured around the urea water suction port 24. Therefore, the urea water in the urea water tank 21 can be sufficiently supplied from the tank 21 to the urea water addition valve 15, and as a result, an amount of urea water corresponding to the control amount calculated as the amount to be added is added. Addition can be supplied from the valve 15.

  Since the heating element 28 is disposed in the vicinity of the urea water suction port 24, the frozen urea water can be thawed in order from the periphery of the urea water suction port 24. Focusing on this point, the position where the melting point (minus 11 ° C.) of the urea water is estimated based on the temperature gradient around the urea water inlet 24 is used. Can be estimated. Further, since the distance from the urea water inlet 24 at the boundary point (thawing distance LN) is calculated, the amount of urea water present around the urea water inlet 24 based on the calculated thawing distance LN. Can be estimated.

  The urea water pump 23 can be operated according to the amount of urea water accumulated around the urea water suction port 24. As a result, the pump operation can be performed in a state where a sufficient amount of urea water is secured around the urea water suction port 24, and as a result, an excessive load on the urea water pump 23 can be suppressed. .

  As the urea water temperature sensor 31, a first sensor 31 a and a second sensor 31 b are disposed at positions where the distance from the urea water suction port 24 is different, and the surroundings of the urea water suction port 24 are based on the temperature measurement values of these two sensors. Since the temperature gradient is estimated, the temperature distribution around the urea water inlet 24 can be detected by measuring the urea water temperature TN at two points.

  The first sensor 31a is provided in the vicinity of the urea water inlet 24, and the second sensor 31b is provided on a straight line connecting the urea water inlet 24 and the first sensor 31a at a position away from the urea water inlet 24. The temperature gradient in the direction away from the urea water inlet 24 can be accurately estimated. Further, since the measurement points of the first sensor 31a and the second sensor 31b are determined so that the determination value Lα exists between the temperature measurement point of the first sensor 31a and the temperature measurement point of the second sensor 31b, urea water is used. This is suitable for accurately estimating the temperature gradient around the suction port 24.

  Since the heating means is an electric heater, the temperature fluctuation around the urea water inlet 24 can be reduced and the temperature distribution can be estimated as compared with, for example, the case where the urea water is thawed using engine cooling water. It is suitable for.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  At least one urea water temperature sensor 31 that measures the urea water temperature TN at a predetermined measurement point in the urea water tank 21 and an outside air temperature sensor that measures the atmospheric temperature (outside air temperature) outside the urea water tank 21 are provided. The temperature distribution around the urea water inlet 24 is estimated based on the measured values of the urea water temperature sensor 31 and the outside air temperature sensor. FIG. 4 shows a temperature distribution diagram around the urea water inlet 24 when the frozen urea water transitions from the solid state to the liquid state. In the present embodiment, the temperature measured by the outside air temperature sensor 33 is regarded as the urea water temperature near the side wall 21 a of the urea water tank 21. Similarly to the above embodiment, assuming that there is a proportional relationship between the distance from the heating element 28 (distance from the urea water inlet 24) and the urea water temperature, the measured temperature value of the urea water temperature sensor 31 and the outside air temperature sensor 33 The distance L at which the urea water temperature TN = −11 ° C. is calculated based on the measured temperature value. At this time, the urea water temperature sensor 31 may be disposed in the vicinity of the urea water inlet 24. The distance L1 from the urea water inlet 24 to the urea water temperature sensor 31 and the distance L3 from the urea water inlet 24 to the side wall of the urea water tank 21 are stored in the ECU 40 in advance. Further, three or more urea water temperature sensors 31 having different distances from the urea water inlet 24 may be provided in the urea water tank 21.

  The urea water temperature TN in the vicinity of the urea water suction port 24 is measured by the first sensor 31a, and the urea water suction port 24 is measured using the temperature measurement value and the temperature measurement value at a position away from the urea water suction port 24. The temperature gradient in the vicinity of the water is estimated, but this is changed, the urea water temperature TN at or near the urea water inlet 24 is estimated, the temperature estimated value, and the position away from the urea water inlet 24 The temperature gradient around the urea water inlet 24 is estimated using the measured temperature value. For example, as shown in FIG. 5, a urea water temperature sensor 31 having a measurement point at a position (point E in the figure) that is a distance L4 away from the urea water inlet 24 is provided. Further, the urea water temperature TN at the urea water suction port 24 (point H in the figure) is calculated based on the heat generation amount of the heating element 28. And the urea water temperature TN between HE is defined by a linear function. Thereby, the temperature distribution around the urea water inlet 24 can be estimated.

  At least one urea water temperature sensor 31 is provided at a position where it is determined that thawed urea water is sufficiently secured around the urea water suction port 24, and the temperature measurement value is a temperature at which urea water can be added (for example, minus 11 ° C.). ) Add urea water in the above cases. According to this configuration, it is possible to estimate the temperature distribution around the urea water inlet 24 by measuring the urea water temperature TN at least at one point and by measuring the outside air temperature.

  The urea water addition amount from the urea water addition valve 15 is limited according to the thawing distance LM calculated in step S14 in FIG. That is, when the urea water that can be sucked up by the urea water pump 23 is small around the urea water suction port 24, the urea water addition amount is reduced according to the amount that can be sucked up. For example, the basic addition amount QNH calculated according to the NOx amount in the exhaust gas, etc. is multiplied by the correction coefficient K according to the thawing distance LN, and the urea water pump 23 is driven and controlled based on the value after the multiplication. . FIG. 6 shows the relationship between the decompression distance LN and the correction coefficient K. According to FIG. 6, in the range where the thawing distance LN is up to the determination value LTH, the correction coefficient K is increased as the thawing distance LN increases, considering that there is less liquid urea water around the urea water inlet 24. It is. Further, in the range of the determination value LTH or more, the correction coefficient K is set to a value 1 assuming that there is sufficient liquid urea water around the urea water suction port 24.

  -Although the heating means is an electric heater, this is changed to a cooling water passage as an engine cooling water passage. For example, a cooling water passage is provided in the urea water tank 21 and the engine cooling water is circulated in the order of “engine body → urea water tank 21 → engine body” by driving an engine-driven water pump. Thereby, the exhaust heat of the engine is used to prevent freezing of the urea water in the urea water tank 21 and to perform thawing at the time of freezing of the urea water. Similarly to the heater, the cooling water passage may be disposed so that the urea water in the vicinity of the urea water suction port 24 can be heated.

  Although the urea water is added when the thawing distance LM is larger than the determination value Lα, the urea water amount Qu in a liquid state is calculated from the thawing distance LM, and the urea water amount Qu is calculated from the determination value. If it is larger, urea water may be added.

  -After the engine is started, a freezing determination for determining that the urea water in the urea water tank 21 is frozen is performed, and when it is determined that the urea water is frozen as a result of the freezing determination, the above-described FIG. It is set as the structure which implements a process. As the freezing determination method, for example, it is performed depending on whether or not the line pressure PNH is equal to or higher than a predetermined pressure when the urea water pump 23 is driven. At this time, when the line pressure PNH is less than the predetermined pressure, it is determined that the urea water is in a frozen state. Alternatively, the freezing determination is performed based on the measured value of the urea water temperature sensor 31. Specifically, the urea water temperature TN at the time of starting the engine is measured by the urea water temperature sensor 31, and when the temperature TN is equal to or lower than a determination value (for example, minus 11 ° C.), it is determined that it is in a frozen state.

  Although the heating element 28 as a heating means is arranged in the vicinity of the urea water inlet 24, the arrangement location of the heating element 28 is not particularly limited, and may be provided at a position separated from the urea water inlet 24. Good. Even in this case, if the temperature distribution in the urea water tank 21 or the outside air temperature is detected and the temperature distribution around the urea water inlet 24 can be estimated, the thawing distance LM can be calculated based on the temperature distribution.

  A so-called in-line system in which the urea water pump 23 is provided in the middle of the urea water supply pipe 22 without being immersed in the urea water in the urea water tank 21 is applied to the present invention. A so-called in-tank system provided in a state of being immersed in urea water in 21 may be applied to the present invention. In such a case, the urea water around the urea water inlet 24 and the urea water pump 23 has been thawed in order to avoid driving the pump 23 while the urea water in the urea water pump 23 is frozen. Is determined based on the thawing distance LM, and the urea water pump 23 may be driven.

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

  DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe, 12 ... DPF, 13 ... SCR catalyst (selective reduction type catalyst), 15 ... Urea water addition valve (reducing agent addition device), 21 ... Urea water tank (reducing agent tank), 23 ... Urea water pump ( (Reducing agent pump), 24 ... suction port, 28 ... heating element (heating means), 31 ... urea water temperature sensor (reducing agent temperature measuring means), 31a ... first sensor, 31b ... second sensor, 32 ... urea water pressure sensor, 33 ... Outside air temperature sensor (outside air temperature measuring means), 40 ... ECU (thawing determination means, addition control means, temperature distribution estimation means).

Claims (6)

A reducing agent tank for storing a reducing agent solution having a predetermined concentration; a selective reduction catalyst provided in an exhaust passage of an internal combustion engine for selectively purifying NOx in exhaust gas by the reducing agent solution; and a reduction in the reducing agent tank Heating means for heating the agent solution, and is applied to an exhaust gas purification system in which the reducing agent solution is added by a reducing agent addition device to the exhaust upstream side of the selective reduction catalyst,
At the time of heating and thawing the reducing agent solution by the heating means, based on the temperature distribution in the surrounding tank around the reducing agent suction port arranged in the reducing agent tank, the surroundings around the reducing agent suction port Thawing determination means for determining the thawing state of the reducing agent solution;
An addition control means for performing addition control of the reducing agent solution by the reducing agent addition device based on the thawing state of the reducing agent solution around the reducing agent suction port determined by the thawing determination means;
An exhaust purification system control apparatus comprising: The heating means is provided in the vicinity of the reducing agent suction port,
The thawing determination means estimates a position that is equivalent to the melting point of the reducing agent solution based on the temperature distribution, and based on the distance from the reducing agent suction port at the same position, around the reducing agent suction port. The exhaust purification system control device according to claim 1, wherein the thawing state of the reducing agent solution is determined. Reducing agent temperature measuring means for measuring the temperature of the reducing agent solution at a plurality of measurement points at different distances from the reducing agent suction port;
Temperature distribution estimation means for estimating the temperature distribution in the tank based on temperature measurement values at each measurement point by the reducing agent temperature measurement means;
With
3. The exhaust according to claim 1, wherein the thawing determination unit determines a thawing state of the reducing agent solution around the reducing agent suction port based on a temperature distribution in the tank estimated by the temperature distribution estimating unit. Purification system control device. Reducing agent temperature measuring means for measuring the temperature of the reducing agent solution at a predetermined measurement point;
An outside air temperature measuring means for measuring the outside air temperature;
A temperature distribution estimation means for estimating the temperature distribution in the tank based on the temperature measurement value at the measurement point by the reducing agent temperature measurement means and the measurement value of the outside air temperature by the outside air temperature measurement means;
With
3. The exhaust according to claim 1, wherein the thawing determination unit determines a thawing state of the reducing agent solution around the reducing agent suction port based on a temperature distribution in the tank estimated by the temperature distribution estimating unit. Purification system control device. Reducing agent temperature measuring means for measuring the temperature of the reducing agent solution at a predetermined measurement point;
Reducing agent temperature estimating means for estimating the temperature of the reducing agent solution at or near the reducing agent suction port;
Temperature distribution for estimating the temperature distribution in the tank based on the measured temperature value at the measurement point by the reducing agent temperature measuring means and the estimated temperature value at or near the reducing agent suction port by the reducing agent temperature estimating means An estimation means;
With
3. The exhaust according to claim 1, wherein the thawing determination unit determines a thawing state of the reducing agent solution around the reducing agent suction port based on a temperature distribution in the tank estimated by the temperature distribution estimating unit. Purification system control device.   The control device for an exhaust purification system according to any one of claims 1 to 5, wherein the heating means is an electric heater.

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