JP2020133501A - Exhaust gas purification control device - Google Patents

Abstract

To provide an exhaust gas purification control device enabling reduction in occasions of repeated thawing and freezing of urea water.SOLUTION: An exhaust gas purification control device includes a residual amount acquisition section, an urea water temperature acquisition section, an outside air temperature acquisition section, a freezing determination section, a thawing control section and a post-thawing control section. In Step S2, the freezing determination section determines whether urea water is in a frozen state or a molten state on the basis of an urea water temperature. In Step S3, when the frozen state is determined (Yes in S2), the thawing control section calculates electric power amount required for thawing as thawing electric power amount, on the basis of residual urea water amount and the urea water temperature. In addition, the thawing control section performs energization control so as to supply the thawing electric power amount to an electric heater. In Step S6, when the molten state is determined (No in S2), the post-thawing control section calculates electric power amount corresponding to the residual urea water amount, the urea water temperature and an outside air temperature as post-thawing electric power amount. In addition, the post-thawing control section performs energization control so as to supply the post-thawing electric power amount to the electric heater.SELECTED DRAWING: Figure 2

Description

The disclosure in this specification relates to an exhaust purification control device applied to a urea water injection system that injects urea water into an exhaust passage of an internal combustion engine.

The urea water injection system shown in Patent Document 1 includes a pump that sucks and discharges urea water stored in a tank, an injector that injects urea water discharged from the pump into an exhaust passage, and a tank that is stored in the tank. It is equipped with an electric heater that heats the urea water. This electric heater is for thawing the urea water frozen in the tank.

The power supplied to the electric heater is calculated based on the remaining amount of urea water stored in the tank and the temperature of the urea water. Then, when the thawing is completed, the energization of the electric heater is stopped.

Japanese Unexamined Patent Publication No. 2016-84723

However, in a situation where the outside air temperature is extremely lower than the freezing temperature of the urea water, when the thawing is completed and the energization of the electric heater is stopped, a part of the urea water may freeze again. In that case, even if the electric heater is re-energized and thawed, the following problems occur due to repeated thawing and freezing. That is, when thawing and freezing are repeated in this way, phase changes between the liquid phase and the solid phase are repeatedly generated, and when the phase changes are repeated in this way, the urea component is likely to be precipitated from the urea water. The precipitated urea component (precipitate) causes, for example, to clog the injection hole or sliding gap of the injector into which urea water is injected.

An object of the disclosure of the present specification is to provide an exhaust gas purification control device that reduces the chance of repeated thawing and freezing of urea water.

One disclosed aspect of achieving the above objectives is
A tank (40) for storing urea water, an injector (20) for injecting the urea water stored in the tank into the exhaust passage (10a) of the internal combustion engine, and an injector for sucking the urea water stored in the tank. An exhaust purification control device applied to a urea water injection system including an electric pump (30) for discharging to and an electric heater (61) for heating urea water stored in a tank.
The remaining amount acquisition unit (S36) that acquires the remaining amount of urea water stored in the tank as the remaining amount of urea water, and
The urea water temperature acquisition unit (S37) that acquires the temperature of the urea water stored in the tank as the urea water temperature, and
The outside air temperature acquisition unit (S38), which acquires the ambient temperature of the tank as the outside air temperature,
A freeze determination unit (S2) that determines whether the urea water is in a frozen state or a molten state based on the urea water temperature, and
When it is determined to be in a frozen state, the amount of power required for thawing is calculated as the amount of thawing power (Q1) based on the remaining amount of urea water and the temperature of the urea water, and energization control is performed so that the amount of thawing power is supplied to the electric heater. Defrost control unit (S3) and
When it is determined to be in a molten state, the amount of power corresponding to the remaining amount of urea water, the temperature of urea water, and the temperature of the outside air is calculated as the amount of power after thawing, and energization control is performed so that the amount of power after thawing is supplied to the electric heater. After thawing, control unit (S6) and
It is an exhaust gas purification control device equipped with.

According to the above aspect, since the control unit is provided after thawing, electric power is supplied to the electric heater even when it is determined that the state is melted, and the possibility of freezing again after thawing can be reduced. Therefore, it is possible to suppress the repetition of the phase change due to the repetition of thawing and freezing, and it is possible to avoid the situation where the urea component is likely to be precipitated. Moreover, according to the above aspect, the electric energy after thawing is calculated according to the outside air temperature in addition to the urea water remaining amount and the urea water temperature. Therefore, even when the outside air temperature is extremely lower than the freezing temperature, the amount of power after thawing is calculated in consideration of the situation, so that the excess or deficiency of the amount of power after thawing can be suppressed.

The reference numbers in parentheses are merely examples of the correspondence with the specific configuration in the embodiment described later, and do not limit the technical scope at all.

It is a figure which shows schematic outline of the urea water injection system which concerns on 1st Embodiment. FIG. 5 is a flowchart showing a processing procedure when the control device shown in FIG. 1 controls the operation of the urea water injection system. It is a flowchart which shows the processing procedure of the defrosting control described in FIG. It is a flowchart which shows the processing procedure of the exhaust gas purification control described in FIG. It is a flowchart which shows the processing procedure of the control after defrosting which is described in FIG. It is a time chart which shows one aspect of the time change of various physical quantities when the control described in FIG. 2 is executed.

Hereinafter, a plurality of embodiments of the present disclosure will be described with reference to the drawings. In addition, duplicate description may be omitted by assigning the same reference numerals to the corresponding components in each embodiment. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other parts of the configuration.

(First Embodiment)
First, the configuration of the urea water injection system to which the exhaust gas purification control device according to the present embodiment is applied will be described with reference to FIG.

The urea water injection system is installed in a vehicle equipped with an internal combustion engine. A purification device having an SCR (Selective Catalytic Reduction) catalyst 11 is attached to the exhaust pipe 10 of the internal combustion engine. The SCR catalyst 11 selectively reduces and purifies nitrogen oxides (NOx) among the oxides in the exhaust gas. The urea water injection system injects urea water into the exhaust passage 10a inside the exhaust pipe 10. The injected urea water is heated in the exhaust passage 10a and hydrolyzed. By this hydrolysis, ammonia as a reducing agent is generated and supplied to the SCR catalyst 11.

The urea water injection system includes an injector 20, an electric pump 30, a tank 40, various pipes, an electric heater, and a control device 70.

The injector 20 is attached to a portion of the exhaust pipe 10 on the upstream side of the exhaust flow with respect to the SCR catalyst 11. The injector 20 injects urea water stored in the tank 40 into the upstream portion of the exhaust passage 10a of the SCR catalyst 11. The injector 20 includes a nozzle body, a main body, a valve body, and an electric actuator. The electric actuator and the injection hole body are attached and held to the main body. The portion of the injection hole body in which the injection hole is formed is exposed to the exhaust passage 10a and is exposed to the exhaust gas.

A nozzle for injecting urea water is formed in the nozzle body. An internal passage that guides urea water to the injection hole is formed in the main body. The valve body opens and closes the injection hole by opening and closing the internal passage, and switches between the injection of urea water and the stop of injection. The electric actuator has an electromagnetic coil that generates a magnetic field by energization, generates an electromagnetic attraction force by energizing the electromagnetic coil, and opens the valve body by the electromagnetic attraction force. When the energization of the electromagnetic coil is stopped, the valve body closes due to the elastic force of the elastic member.

The electric pump 30 has an impeller, a casing, a motor, and the like. The impeller is held in a rotatable state in the casing. The impeller is rotationally driven by the above motor. For example, the motor is a three-phase brushless motor, and the rotation speed is controlled by sinusoidal output current control. That is, the rotation speed of the impeller is controlled by controlling the energization cycle, energization phase, and current peak value of the drive current energized to the coils of each phase.

The various pipes described above include the discharge pipe 51, the suction pipe 52, and the return pipe 53 described below. The discharge pipe 51 connects the inflow port of the injector 20 and the discharge port of the electric pump 30. The urea water discharged from the electric pump 30 is supplied to the injector 20 through the discharge pipe 51. The suction pipe 52 connects the suction port of the electric pump 30 and the tank 40. The urea water stored in the tank 40 is sucked into the electric pump 30 through the suction pipe 52. The return pipe 53 connects the discharge port or the discharge pipe 51 of the electric pump 30 to the tank 40. The urea water discharged from the electric pump 30 is returned to the tank 40 through the return pipe 53 when the injector 20 is closed.

The electric heater described above includes the tank heater 61, the suction pipe heater 62, and the return pipe heater 63 described below. The tank heater 61 is attached to a recess formed in the bottom wall of the tank 40. The tank heater 61 heats the urea water stored in the tank 40 by heating the tank 40. The suction pipe heater 62 is attached to the suction pipe 52. The suction pipe heater 62 heats the urea water located in the suction pipe 52 by heating the suction pipe 52. The return pipe heater 63 is attached to the return pipe 53. The return pipe heater 63 heats the urea water located in the return pipe 53 by heating the return pipe 53.

In the present embodiment, the discharge pipe 51 and the injector 20 are not provided with an electric heater, but an electric heater may be attached to these to be heated. However, since the injector 20 is heated by the exhaust gas flowing through the exhaust passage 10a, it is less likely to fall below the freezing temperature than the tank 40 and various pipes, and the need for heating by an electric heater is low.

The control device 70 has at least one arithmetic processing unit (processor 71) and at least one storage device (memory 72) as a storage medium for storing programs and data executed by the processor 71. Further, the control device 70 includes a heater drive circuit 73, and an injector drive circuit and a pump drive circuit (not shown). These drive circuits have a switching element that switches between energization and interruption of in-vehicle battery power.

The processor 71 and the memory 72 may be provided by a microcomputer (microcomputer). The storage medium is a non-transitional substantive storage medium that non-temporarily stores a program that can be read by the processor 71. The storage medium may be provided by a semiconductor memory, a magnetic disk, or the like. The control device 70 may be provided by one computer, or a set of computer resources linked by a data communication device. By being executed by the processor 71, the program causes the control device 70 to function as the device described herein and to perform the methods described herein.

The control device 70 includes an injector control unit M1, a pump control unit M2, and a heater control unit M3. These control units are realized by the control device 70 when the processor 71 executes a program stored in the memory 72. Detection signals detected by various sensors described later are input to the control device 70. Based on these detection signals, the above-mentioned control unit executes various controls.

The injector control unit M1 controls the valve opening operation of the valve body of the injector 20 by controlling the energization state of the injector 20 to the electromagnetic coil, and controls the injection amount and injection timing of urea water. For example, the injector control unit M1 controls the valve opening time of the valve body by controlling the energization time of the electromagnetic coil, and controls the injection amount of urea water injected per unit time.

The control device 70 requires urea water injection from the injector 20 when exhaust gas purification is required due to the operation of the internal combustion engine and the conditions such as the SCR catalyst 11 being above the activation temperature are satisfied. To do. Further, the control device 70 calculates the target injection amount of urea water based on the amount of NOx discharged from the internal combustion engine. The injector control unit M1 controls the operation of the injector 20 so that the valve body is opened at the valve opening time corresponding to the target injection amount when the urea water injection is requested.

The pump control unit M2 controls the rotation speed of the impeller by controlling the energization state of the electric pump 30 to the motor, and controls the discharge pressure P of urea water and the discharge timing. For example, the pump control unit M2 controls the power supply to the motor and controls the discharge pressure P by controlling the energization cycle, energization phase, and current peak value of the drive current flowing through the coil of the motor.

The heater control unit M3 controls the temperature of the urea water in the tank 40, the suction pipe 52, and the return pipe 53 by controlling the energization state of the tank heater 61, the suction pipe heater 62, and the return pipe heater 63. For example, the heater control unit M3 controls the amount of electric power to be supplied by duty-controlling the drive current flowing through various electric heaters.

The various sensors described above include an outside air temperature sensor 81, a urea water temperature sensor 82, a concentration sensor 83, a liquid level sensor 84, and a pressure sensor 85. The outside air temperature sensor 81 is arranged outside the tank 40. The outside air temperature sensor 81 outputs a detection signal according to the ambient temperature of the tank 40.

The urea water temperature sensor 82, the concentration sensor 83, and the liquid level sensor 84 are attached to the tank 40. The urea water temperature sensor 82 outputs a detection signal according to the urea water temperature in the tank 40. The concentration sensor 83 outputs a detection signal according to the ratio of the urea component (urea water concentration α) contained in the urea water in the tank 40. The liquid level sensor 84 outputs a detection signal according to the liquid level height of the urea water in the tank 40.

The pressure sensor 85 is attached to the discharge port or the discharge pipe 51 of the electric pump 30. The pressure sensor 85 outputs a detection signal according to the pressure (discharge pressure P) of the urea water discharged from the electric pump 30.

It can be said that the heater control unit M3 includes an outside air temperature acquisition unit M31, a urea water temperature acquisition unit M32, a concentration acquisition unit M33, a liquid level height acquisition unit M34, and a discharge pressure acquisition unit M35. The outside air temperature acquisition unit M31 acquires the outside air temperature Ta by calculating the outside air temperature Ta based on the detection signal output from the outside air temperature sensor 81. The urea water temperature acquisition unit M32 acquires the urea water temperature Tu by calculating the urea water temperature Tu based on the detection signal output from the urea water temperature sensor 82. The concentration acquisition unit M33 acquires the urea water concentration α by calculating the urea water concentration α based on the detection signal output from the concentration sensor 83. The liquid level height acquisition unit M34 acquires the liquid level height L by calculating the liquid level height L based on the detection signal output from the liquid level sensor 84.

Next, a procedure for controlling the energized state of the electric heater based on various physical quantities acquired by these acquisition units will be described with reference to FIGS. 2 to 5. The process of FIG. 2 is executed while the internal combustion engine is in an operable state or is in operation, such as when the ignition switch is turned on. Further, the flowcharts shown in FIGS. 3 to 5 are repeatedly executed by the processor 71 at a predetermined calculation cycle.

First, in step S1 of FIG. 2, the urea water temperature Tu is measured by the urea water temperature acquisition unit M32. In the following step S2, it is determined whether or not the measured urea water temperature Tu is equal to or lower than the freezing temperature T1 of the urea water. The freezing temperature T1 is set to a preset ideal freezing temperature (for example, −11 ° C.) of the urea water concentration α (for example, 32.5%). Alternatively, the freezing temperature T1 used in this determination is set to a value lower than the ideal freezing temperature of the urea water concentration by a marginal temperature.

When it is determined that the urea water temperature Tu is equal to or lower than the freezing temperature T1 of the urea water, it is considered that the urea water in the tank 40 is frozen, and the thawing control is executed in the following step S3. When it is determined that the urea water temperature Tu is not equal to or lower than the urea water freezing temperature T1, it is determined in the subsequent step S4 whether or not there is a request for urea water injection. If there is an injection request, the exhaust gas purification control is executed in the following step S5. If there is no injection request, post-thawing control is executed in the following step S6.

Next, the processing procedure of the defrosting control executed in step S3 of FIG. 2 will be described with reference to FIG. First, in step S10, the concentration acquisition unit M33 measures the urea water concentration α. In the following step S11, the liquid level height L is measured by the liquid level height acquisition unit M34. In the following step S12, the remaining amount of urea water M [kg] is calculated based on the measured urea water concentration α and the liquid level height L. For example, the urea water remaining amount M is calculated according to the simultaneous equations of the following equations 1 and 2. S in Equation 1 is a constant indicating the liquid level area of the tank 40. 1.09 × 10 ³ [kg / m ³ ] in Equation 2 is the density when the urea water concentration is 3.25%.

In the following step S13, the urea water temperature Tu is measured by the urea water temperature acquisition unit M32. In the following step S14, the thawing power amount Q1 is calculated based on the urea water remaining amount M and the urea water temperature Tu. The thawing electric energy Q1 is calculated as a value required for thawing all of the urea water remaining amount M. For example, the defrosting electric energy Q1 is calculated according to the simultaneous equations of Equation 3 below. C in Equation 3 is the specific heat capacity of urea water.

In the following step S15, the energization of the tank heater 61 is controlled so as to supply the electric energy of the defrosting electric energy Q1. For example, the duty of the heater drive current is controlled so that the defrosting electric energy Q1 is supplied in a predetermined time. In the following step S16, the energization of the electric pump 30 to the motor is stopped, and the electric pump 30 is stopped. In the following step S17, the energization of the injector 20 to the electromagnetic coil is stopped, and the valve opening operation of the injector 20 is stopped.

Next, the processing procedure of the exhaust gas purification control executed in step S5 of FIG. 2 will be described with reference to FIG. First, in step S20, the motor of the electric pump 30 is driven so that the discharge pressure P becomes the target pressure. For example, the above-mentioned sinusoidal output current control is executed at the current peak value corresponding to the target pressure. The target pressure is set to a value higher than the upper limit pressure P2 described later.

In the following step S21, the actual discharge pressure P is measured by the discharge pressure acquisition unit M35. In the following step S22, it is determined whether or not the measured discharge pressure P is higher than the upper limit pressure P2. When it is determined in step S22 that the discharge pressure P is higher than the upper limit pressure P2, the electric pump 30 is in a state of normally discharging urea water, and the inside of the tank 40 and various pipes. It is considered that all the urea water in the above is in a completely melted state. Then, in the following step S23, the energization state of the injector 20 is controlled so as to inject urea water at the above-mentioned target injection amount according to the NOx amount. In the following step S24, the energization of the electric heater is turned off.

On the other hand, when it is determined in step S22 that the discharge pressure P is equal to or lower than the upper limit pressure P2, it is considered that a part of the urea water is in a partially frozen state. Further, it is considered that the discharge pressure P is lowered due to such partial freezing. Then, the post-decompression control according to step S6 of FIG. 2 is executed.

Next, the processing procedure of post-defrosting control executed in step S6 of FIG. 2 will be described with reference to FIG. First, in steps S30 to S33, the motor of the electric pump 30 is feedback-controlled so that the discharge pressure P becomes the lower limit pressure P1 or more and the upper limit pressure P2 or less. Specifically, the electric pump 30 is driven in step S30, the discharge pressure P is measured in step S31, and if it is determined in step S32 that P1 ≦ P ≦ P2 is not satisfied, the drive current of the electric pump 30 is increased in step S33. adjust.

When it is determined in step S32 that P1 ≦ P ≦ P2, in steps S34 to S37, the urea water remaining amount M is calculated in the same manner as in steps S10 to S13 of FIG. 3, and the urea water temperature Tu is measured. In the following step S38, the outside air temperature Ta is measured by the outside air temperature acquisition unit M31. In the following step S39, the temperature difference ΔT between the urea water temperature Tu and the outside air temperature Ta is calculated. The temperature difference ΔT is a value obtained by subtracting the outside air temperature Ta from the urea water temperature Tu.

In the following step S40, the deviation amount Δα of the urea water concentration α with respect to the target concentration (for example, 32.5%) is calculated. The deviation amount Δα is a value obtained by subtracting the target concentration from the urea water concentration α. In the following step S41, it is determined whether or not the deviation amount Δα is equal to or greater than a predetermined value (for example, 0.5%).

When the deviation amount Δα is determined to be equal to or higher than a predetermined value in step S41, the concentration maintenance power amount Q2 is calculated in step S42 based on the urea water remaining amount M, the temperature difference ΔT, and the urea water concentration α. The concentration maintenance electric energy Q2 is calculated as a value required to prevent the urea water from being thawed again and falling into a partially melted state when all of the urea water has been thawed. For example, the concentration maintenance electric energy Q2 is calculated according to the simultaneous equations of the following equations 4 and 5.

K _{Q in} Equations 4 and 5 is a correction coefficient that takes into consideration the magnitude of the deviation amount Δα for the purpose of maintaining the urea water concentration. That is, the higher the measured urea water concentration α is with respect to the target concentration, the lower the concentration maintenance power amount Q2 is corrected. According to the correction of K _Q , it is suppressed that the water component of the urea water evaporates to a high concentration due to excessive heating, and the deterioration of the quality of the urea water is suppressed.

The concentration maintenance electric energy Q2 calculated by the equations 4 and 5 is set to a larger value as the amount of the urea water remaining amount M to be heated increases. Further, as the outside air temperature Ta is lower and the temperature difference ΔT is larger, the concentration maintenance electric energy Q2 is set to a larger value.

In the following step S43, the energization of the tank heater 61 is controlled so as to supply the electric energy of the concentration maintenance electric energy Q2. For example, the duty of the heater drive current is controlled so that the concentration maintenance electric energy Q2 is supplied in a predetermined time.

If the deviation amount Δα is less than a predetermined value in step S41, the melting maintenance power amount Q3 is calculated in step S44 based on the urea water remaining amount M, the temperature difference ΔT, and the urea water temperature Tu. The melting maintenance electric energy Q3 is calculated as a value required to start thawing again in a state where all of the urea water has been thawed and prevent the state from falling into a partially melted state. For example, the melting maintenance electric energy Q3 is calculated according to the simultaneous equations of the following equations 6 and 7.

_{KT in} Equations 6 and 7 is a correction coefficient considering the difference between the urea water temperature Tu and the freezing temperature T1 for the purpose of preventing the urea water refreezing. That is, the higher the measured urea water temperature Tu and the larger the difference from the freezing temperature T1, the lower the melting maintenance power amount Q3 is corrected. According to the correction of _KT , it is suppressed that the water component of the urea water evaporates to a high concentration due to excessive heating, and the deterioration of the quality of the urea water is suppressed. Comparing the concentration maintenance electric energy Q2 and the melt maintenance electric energy Q3, if the urea water remaining amount M and the temperature difference ΔT are the same, the concentration maintenance electric energy Q2 is higher than the melt maintenance electric energy Q3 by the amount of the higher concentration. It will be set to a small value.

In the following step S45, the energization of the tank heater 61 is controlled so as to supply the electric energy of the melting maintenance electric energy Q3. For example, the duty of the heater drive current is controlled so that the melt maintenance electric energy Q3 is supplied in a predetermined time.

Next, an example of the operation of the urea water injection system according to the present embodiment will be described with reference to FIG. The operation of the internal combustion engine is started at t10 in the figure.

During the period from t10 to t20, the urea water temperature Tu is below the freezing temperature T1 (see column a). Therefore, decompression control is executed during this period. That is, the energization of the electric pump 30 is turned off (see column f), and the energization of the injector 20 is turned off (see column g). Then, the tank heater 61 is energized with the electric power based on the defrosting electric energy Q1. The power consumption is set so that the defrosting electric energy Q1 is supplied during the period from the time t10 to the time t20.

The injector 20 is heated by the exhaust gas flowing through the exhaust passage 10a, and the temperature of the urea water in the injector 20 rises. Then, the heat of the exhaust gas also raises the urea water temperature Tu in the tank 40 and the ambient temperature (outside air temperature Ta) of the tank 40 (see columns a and b).

After that, the urea water is heated by the thawing control, the urea water temperature Tu rises, and at t20 when the freezing temperature T1 is reached, the thawing control is switched to the post-thaw control. That is, the energization of the electric pump 30 is turned on (see column f), and the energization of the injector 20 is turned off (see column g). The current consumption of the electric pump 30 in the post-thawing control is set to a value smaller than the current consumption in the exhaust gas purification control (see column f). The discharge pressure P in the control after thawing is adjusted in the range from the lower limit pressure P1 to the upper limit pressure P2 (see column c).

Further, in the post-thawing control, the tank heater 61 is energized with the electric power based on the concentration maintenance electric energy Q2 or the melting maintenance electric energy Q3 (see column h). The power consumption is set so that the concentration maintenance power amount Q2 or the melting maintenance power amount Q3 is supplied during the period from the time t20 to the time t30. The urea water concentration is maintained in the normal range from the lower limit value α1 to the upper limit value α2 (see column e).

After that, at t30 when the request for urea water injection was made, the post-thawing control was switched to the exhaust purification control. That is, the energization of the electric pump 30 is turned on (see column f), and the energization of the injector 20 is turned on (see column g). Then, the energization of various electric heaters is turned off (see column h).

Based on the above, the exhaust gas purification control device according to the present embodiment includes a remaining amount acquisition unit, a urea water temperature acquisition unit, an outside air temperature acquisition unit, a freezing determination unit, a thawing control unit, and a post-thawing control unit, which will be described below. I can say.

The "remaining amount acquisition unit" corresponds to the processor 71 when the step S36 is being executed, and acquires the remaining amount of urea water stored in the tank 40 as the urea water remaining amount M. The "urea water temperature acquisition unit" corresponds to the processor 71 when the step S37 is being executed, and acquires the temperature of the urea water stored in the tank 40 as the urea water temperature Tu. The “outside air temperature acquisition unit” corresponds to the processor 71 when the step S38 is being executed, and acquires the ambient temperature of the tank 40 as the outside air temperature Ta. The “freezing determination unit” corresponds to the processor 71 when the step S2 is being executed, and determines whether the urea water is in the frozen state or the molten state based on the urea water temperature Tu.

The “decompression control unit” corresponds to the processor 71 when the step S3 is being executed. When the thawing control unit is determined to be in a frozen state, the thawing power amount Q1 is calculated as the thawing power amount Q1 based on the urea water remaining amount M and the urea water temperature Tu, and the thawing power amount Q1 is the tank heater 61. Energization control is performed so as to supply to. The “post-decompression control unit” corresponds to the processor 71 when the step S6 is being executed. When it is determined that the thawed state is in a molten state, the post-thaw control unit calculates the amount of power corresponding to the remaining amount of urea water M, the urea water temperature Tu, and the outside air temperature Ta as the amount of power after thawing, and calculates the amount of power after thawing. Energization control is performed so as to supply to the tank heater 61. The "power amount after thawing" corresponds to the concentration maintenance power amount Q2 or the melting maintenance power amount Q3.

As described above, since the exhaust gas purification control device according to the present embodiment includes the control unit after thawing, electric power is supplied to the tank heater 61 even when it is determined to be in the molten state, and the exhaust gas purification control device is frozen again after thawing. The risk of this can be reduced. Therefore, it is possible to suppress the repetition of the phase change due to the repetition of thawing and freezing, and it is possible to avoid the situation where the urea component is likely to be precipitated. Moreover, according to the present embodiment, the amount of electricity after thawing is calculated according to the outside air temperature Ta in addition to the urea water remaining amount M and the urea water temperature Tu. Therefore, even when the outside air temperature Ta is extremely lower than the freezing temperature T1, the electric energy after thawing is calculated in consideration of the situation, so that there is a risk of refreezing due to insufficient electric energy after thawing. Can be reduced.

If the phase change between the liquid phase and the solid phase is repeated by repeating thawing and freezing, the urea component is likely to be precipitated from the urea water. The urea component (precipitate) precipitated in this way causes clogging of a narrow portion of the urea water passage, such as the injection hole of the injector 20.

Further, in the present embodiment, the amount of electric power required to maintain the urea water temperature Tu higher than the freezing temperature T1 is defined as the melt maintenance electric energy Q3, and the post-thawing control unit calculates the melt maintenance electric energy Q3 as the post-thawing electric energy. To do. Therefore, the certainty of avoiding refreezing can be improved.

Further, in the present embodiment, the post-thawing control unit calculates the melt maintenance power amount Q3 to a larger value as the outside air temperature Ta is lower than the urea water temperature Tu, that is, the larger the temperature difference ΔT. Therefore, it is possible to improve the certainty of avoiding refreezing due to the low outside air temperature Ta.

Further, in the present embodiment, the amount of electric power required to maintain the concentration of urea water stored in the tank 40 within a predetermined concentration range is defined as the concentration maintenance electric energy Q2. Then, the post-thaw control unit calculates the concentration maintenance power amount Q2 as the post-thaw power amount when the urea water concentration α is outside the predetermined concentration range, and when the urea water concentration α is within the predetermined concentration range, The melting maintenance electric energy Q3 is calculated as the electric energy after thawing.

Further, in the present embodiment, a concentration acquisition unit for acquiring the concentration of urea water stored in the tank 40 is provided, and the post-thawing control unit reduces the amount of melt maintenance power as the concentration is higher than the predetermined concentration range. Calculate to value. The “concentration acquisition unit” corresponds to the processor 71 when the step S34 is being executed. According to this, overheating by the tank heater 61 controlled after thawing is suppressed, the water component of the urea water is suppressed from evaporating to a high concentration, and the quality deterioration of the urea water is suppressed.

Further, the present embodiment includes a post-thawing pump control unit that drives the electric pump 30 during the execution period of post-thawing control. The “post-thaw pump control unit” corresponds to the processor 71 when the step S31 is being executed. According to this, not only the urea water in the tank 40 but also the urea water in the injector 20 and the urea water in the discharge pipe 51 can be efficiently heated, and the refreezing can be suppressed. Can be promoted.

Further, in the present embodiment, even when there is a request for injection of urea water, if the discharge pressure P of the electric pump 30 is unintentionally lowered (S22: No), the drive of the injector 20 is stopped. After thawing, the control unit executes energization control of the tank heater 61. When refreezing occurs, it is highly probable that the discharge pressure P will be lowered unintentionally. In view of this point, when the discharge pressure P is unintentionally lowered, the control is executed after thawing, so that it is possible to avoid a state in which NOx is not purified unintentionally, and it is possible to quickly re-defrost.

(Other embodiments)
In the first embodiment, the concentration maintenance electric energy Q2 and the melting maintenance electric energy Q3 are switched in the post-thawing control, but this switching is abolished and either the concentration maintenance electric energy Q2 or the melting maintenance electric energy Q3 is abolished. One may be abolished.

In the first embodiment, the lower the outside air temperature Ta is lower than the urea water temperature Tu, the larger the melt maintenance electric energy Q3 is calculated. On the other hand, the melting maintenance electric energy Q3 may be calculated based on the history of changes in the outside air temperature Ta. For example, the lower the average temperature of the changing outside air temperature Ta, the larger the melting maintenance power amount Q3 may be calculated.

In the first embodiment, the electric pump 30 is driven for control after thawing, but the electric pump 30 may be driven and stopped for control after thawing.

In the first embodiment, even when there is a request for injection of urea water, if the discharge pressure P is unintentionally lowered, the exhaust gas purification control is switched to the post-thaw control. Such switching may be abolished.

In the first embodiment, the defrosting electric energy Q1 and the defrosting electric energy are calculated for the tank heater 61 among the plurality of electric heaters. That is, the calculated electric energy is the electric energy supplied to the tank heater 61, and is different from the electric energy supplied to other electric heaters. On the other hand, the defrosting electric energy Q1 and the defrosting electric energy may be calculated for all of the tank heater 61, the suction piping heater 62, and the return piping heater 63.

10a Exhaust passage, 20 Injector, 30 Electric pump, 40 tank, 61 Electric heater, 70 Exhaust purification control device, Q1 Thaw power amount, Q2 Concentration maintenance power amount, Q3 Melt maintenance power amount, S2 Freeze judgment unit, S3 Thaw control unit , S30 post-thawing pump control unit, S34 concentration acquisition unit, S36 remaining amount acquisition unit, S37 urea water temperature acquisition unit, S38 outside temperature acquisition unit, S6 post-thawing control unit.

Claims (7)

The tank (40) for storing urea water, the injector (20) for injecting the urea water stored in the tank into the exhaust passage (10a) of the internal combustion engine, and the urea water stored in the tank are sucked in. An exhaust purification control device applied to a urea water injection system including an electric pump (30) for discharging to the injector and an electric heater (61) for heating the urea water stored in the tank.
The remaining amount acquisition unit (S36) for acquiring the remaining amount of urea water stored in the tank as the remaining amount of urea water,
The urea water temperature acquisition unit (S37), which acquires the temperature of the urea water stored in the tank as the urea water temperature,
An outside air temperature acquisition unit (S38) that acquires the ambient temperature of the tank as the outside air temperature,
A freezing determination unit (S2) for determining whether the urea water is in a frozen state or a molten state based on the urea water temperature, and
When it is determined to be in the frozen state, the amount of power required for thawing is calculated as the amount of thawing power (Q1) based on the remaining amount of urea water and the temperature of the urea water, and the amount of thawing power is supplied to the electric heater. The defrost control unit (S3) that controls the energization and
When it is determined to be in the molten state, the electric energy corresponding to the remaining amount of urea water, the urea water temperature, and the outside air temperature is calculated as the electric energy after thawing, and the electric energy after thawing is supplied to the electric heater. After thawing control unit (S6) that controls energization so as to do
Exhaust gas purification control device equipped with. The amount of electric power required to maintain the urea water temperature higher than the freezing temperature is defined as the melt maintenance electric energy (Q3).
The exhaust gas purification control device according to claim 1, wherein the post-thaw control unit calculates the melt maintenance power amount as the post-thaw power amount. The exhaust gas purification control device according to claim 2, wherein the post-thaw control unit calculates the melt maintenance power amount to a larger value as the outside air temperature is lower than the urea water temperature. The amount of power required to maintain the concentration of urea water stored in the tank within a predetermined concentration range is defined as the concentration maintenance power amount (Q2).
The post-thaw control unit calculates the concentration maintenance power amount as the post-thaw power amount when the concentration is outside the predetermined concentration range, and when the concentration is within the predetermined concentration range, the melt maintenance power. The exhaust purification control device according to claim 2 or 3, wherein the amount is calculated as the electric energy after thawing. A concentration acquisition unit (S34) for acquiring the concentration of urea water stored in the tank is provided.
The exhaust gas purification control device according to claim 4, wherein the post-thaw control unit calculates the melt maintenance power amount to a smaller value as the concentration is higher than the predetermined concentration range. The exhaust gas purification control device according to any one of claims 1 to 5, further comprising a post-thaw pump control unit (S30) for driving the electric pump during a period during which the post-thaw control unit executes energization control of the electric heater. .. Even when there is a request to inject urea water, if the discharge pressure of the electric pump is unintentionally lowered, the drive of the injector is stopped, and after thawing, the electric heater is operated by the control unit. The exhaust gas purification control device according to claim 6, wherein the energization control is executed.

Images