JP2008248712A - Exhaust emission control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of immediately discriminating the different kind when any different liquid is mistakenly filled in a reducing agent tank. <P>SOLUTION: The exhaust emission control device includes an electrostatic capacity type water level measuring means for measuring the level of a liquid in a reducing agent tank from the electrostatic capacity between two electrodes hanging into the reducing agent tank parallel to each other, a float type water level measuring means for measuring the level of the liquid in the reducing agent tank by using a float on the liquid in the reducing agent tank, and a different kind discrimination means for discriminating the different kind of the liquid in the reducing agent tank based on the difference between the first level measured by the electrostatic capacity type water level measuring means and the second level measured by the pressure type water level measuring means (Step 1 → Step 2 → Step 3). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine exhaust gas purification device (hereinafter referred to as “exhaust gas purification device”) for reducing and purifying nitrogen oxide (NOx) in exhaust gas, and a technique for discriminating this when a different kind of liquid is put in a reducing agent tank. About.

A liquid reducing agent or its precursor is injected and supplied upstream of the NOx reduction catalyst installed in the engine exhaust system, and the NOx and reducing agent in the exhaust are subjected to a catalytic reduction reaction to purify NOx into harmless components. There has been proposed an exhaust emission control device. In such an exhaust purification device, by using a concentration sensor that measures the concentration of the liquid reducing agent or its precursor from the temperature rise characteristic of the heating element, the liquid reducing agent or its precursor is stored in the reducing agent tank. Japanese Patent Application Laid-Open No. 2006-342882 (Patent Document 1) describes a technique for discriminating that different types of liquids are contained.
JP 2006-342882 A

  In the different kind discrimination technique using the concentration sensor disclosed in Patent Document 1, when light oil or the like is accidentally supplied to the reducing agent tank, the liquid reducing agent remaining in the reducing agent tank or its precursor is consumed. There is an improvement that it is not possible to discriminate between different types until it is finished. When light oil is misfueled, due to the difference in specific gravity, the liquid reducing agent or its precursor and the light oil are two-layered up and down with the light oil as the upper layer in the reducing agent tank. Since the concentration sensor is arranged toward the bottom of the reducing agent tank, it is not possible to discriminate between different types unless the lower liquid reducing agent or its precursor is consumed and the light oil is lowered to the level of the concentration sensor.

  Therefore, in view of such a technical background, an object of the present invention is to propose an exhaust emission control device that can immediately distinguish between different types of liquids such as light oil in the reducing agent tank.

  For this purpose, in the first aspect of the present invention, the exhaust gas purification apparatus uses a reducing agent tank for storing a liquid reducing agent or a precursor thereof, and an exhaust gas using the liquid reducing agent in the reducing agent tank or a precursor thereof. Capacitance type water level measurement that measures the water level of the liquid in the reducing agent tank from the reduction catalyst that reduces and purifies the nitrogen oxides in the inside, and the capacitance between the two electrodes that hang parallel to each other in the reducing agent tank Means, a float type water level measuring means for measuring the water level of the liquid in the reducing agent tank using a float floating on the liquid in the reducing agent tank, and a first measured by the capacitance type water level measuring means. And a different type discriminating unit configured to discriminate between different types of liquid in the reducing agent tank based on a difference between the water level and the second water level measured by the float type water level measuring unit. .

According to a second aspect of the present invention, when the difference value obtained by subtracting the first water level from the second water level exceeds a first threshold value, the different type discrimination means sets the reducing agent tank liquid as a different type liquid. It is characterized by discriminating.
The invention according to claim 3 further includes first notifying means for notifying that the dissimilar liquid has been put into the reducing agent tank when the dissimilarity determining means determines that the dissimilar liquid is a different liquid. To do.

In the invention according to claim 4, when the difference value obtained by subtracting the second water level from the first water level exceeds a second threshold, it is determined that an abnormality has occurred in the reducing agent tank. Further comprising means.
The invention according to claim 5 further includes second notifying means for notifying that an abnormality has occurred in the reducing agent tank when the abnormality determining means has determined that an abnormality has occurred.

  According to the first aspect of the present invention, two types of water level measuring means having different measurement methods are used, and different types are discriminated based on the difference between the water level measurement values. That is, one of the capacitance type water level measuring means is a system that is not suitable for water level measurement with respect to a different kind of liquid other than the liquid reducing agent or its precursor, and the other float type water level measuring means is a float that floats on various liquids. Since the water level can be measured, when there is a difference between the measured values, it can be determined that a different liquid that is not a liquid reducing agent or its precursor is contained. Therefore, even when a different kind of liquid such as light oil that is not mixed with the liquid reducing agent or its precursor and is formed into a two-layered layer is entered, it can be immediately determined.

  According to the second aspect of the present invention, the difference value obtained by subtracting the first water level by the capacitive water level measuring unit from the second water level by the float type water level measuring unit is the first value for removing the measurement error range. When the condition exceeds the threshold, it is determined that the liquid is a different liquid. That is, while the float type water level measuring means can measure the water level with floats floating in various liquids, the capacitance type water level measuring means is not suitable for measuring the water level of different liquids, so the measured value of the float type water level measuring means increases. However, when the measured value of the capacitive water level measuring means does not change, that is, when the difference value obtained by subtracting the first water level from the second water level exceeds the error range, the dissimilar liquid is If it is placed in the reducing agent tank, it can be accurately determined.

According to the third aspect of the present invention, by providing the first notification means for notifying that the different type liquid is put in, it becomes possible to immediately notify the user of the erroneous input of the different type liquid even during the liquid replenishment operation. Therefore, the function of the exhaust gas purification device can be maintained by preventing erroneous replenishment of different liquids.
According to the fourth aspect of the present invention, the difference value obtained by subtracting the second water level by the float type water level measuring means from the first water level by the capacitance type water level measuring means is measured, contrary to the condition for discriminating between different types. When a condition that exceeds the second threshold value for excluding the error range is reached, the condition is a condition that cannot occur if both the water level measuring means function normally. Therefore, an abnormality judging means for judging the condition is provided. Thus, it can be determined that some abnormality has occurred in the reducing agent tank, such as a failure of any water level measuring means.

  According to the invention described in claim 5, by providing the second informing means for informing that an abnormality has occurred in the reducing agent tank, the user can be urged to perform maintenance or repair, and the exhaust purification device The function of can be maintained.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the overall configuration of an exhaust purification device that uses an aqueous urea solution as a precursor of a liquid reducing agent to reduce and purify NOx in engine exhaust.
A nitrogen oxidation catalyst 16 that oxidizes nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ) and an aqueous urea solution are injected along the exhaust circulation direction into the exhaust pipe 14 connected to the exhaust manifold 12 of the engine 10. An injection nozzle 18 for supplying, an NOx reduction catalyst 20 for reducing and purifying NOx using ammonia obtained by hydrolyzing a urea aqueous solution, and an ammonia oxidation catalyst 22 for oxidizing ammonia that has passed through the NOx reduction catalyst 20 Each is arranged. On the other hand, the urea aqueous solution stored in the reducing agent tank 24 is supplied to the injection nozzle 18 via the pump module 26 that sucks and pressure-feeds the urea aqueous solution and the addition module 28 that controls the injection flow rate.

In such an exhaust purification device, the urea aqueous solution injected and supplied from the injection nozzle 18 is hydrolyzed using water vapor in the exhaust and exhaust and converted to ammonia. It is known that the converted ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 20 and is converted into water (H ₂ O) and nitrogen (N ₂ ). At this time, in order to improve the NOx purification efficiency in the NOx reduction catalyst 20, NO by the nitrogen oxidation catalyst 16 is oxidized to NO _2, it is improved in that the ratio between NO and NO ₂ in the exhaust gas suitable for reduction The On the other hand, the ammonia that has passed through the NOx reduction catalyst 20 is oxidized by the ammonia oxidation catalyst 22 disposed downstream of the exhaust gas, so that ammonia is prevented from being released into the atmosphere as it is.

  A sensor 30 that functions as a water level measuring unit is attached to the reducing agent tank 24 in order to measure the water level (liquid level) of the urea aqueous solution. In the sensor 30, a base portion 30 </ b> A containing a circuit board is fixed to the top wall of the reducing agent tank 24, and the electrode portion 30 </ b> B is suspended from the base portion 30 </ b> A to the bottom wall of the reducing agent tank 24. A donut-shaped float 30 </ b> C that passes through the electrode portion 30 </ b> B through the center hole and floats up and down in the liquid is provided.

  The electrode portion 30B has a configuration in which an inner electrode and an outer electrode having a circular cross section are arranged concentrically, that is, in parallel with each other, and serves as a capacitance-type water level measurement unit that measures the water level from the capacitance between the electrodes. Function. The float 30C is embedded with magnets, and a number of reed switches arranged along the longitudinal direction of the electrode portion 30B react to the top and bottom of the float 30C, and the water level is measured from the position of the float 30C. It functions as a float type water level measuring means. In the present embodiment, the sensor 30 in which the electrostatic capacity type water level measuring means and the float type water level measuring means are integrally formed is illustrated, but both types of water level measuring means may be provided separately.

  The two types of water level measurement by the electrode unit 30B and the float 30C have characteristic differences as shown in FIG. That is, in the capacitance-type water level measurement by the electrode unit 30B, for example, when light oil is put in the reducing agent tank 24 as a different liquid, the capacitance of the light oil shows a value equivalent to that of air, and therefore the rise in the water level is measured. I can't. Therefore, even if light oil is added onto the urea aqueous solution remaining in the tank, the water level does not increase (solid line). On the other hand, in the float type water level measurement by the float 30C, since the measurement is performed based on the position of the float 30C floating in the liquid in the tank, if light oil is added, the rise in the water level is measured accordingly (dotted line). Using such a characteristic difference between the two, based on the difference between the measured value of the electrode section 30B whose characteristics change according to the type of liquid and the measured value of the float 30C whose characteristics hardly change, It is possible to determine whether a liquid has entered incorrectly. Hereinafter, the misfueling of light oil will be described as a representative example.

  Capacitance type and float type water level signals output from the base of the sensor 30 are input to a control unit 32 incorporating a computer. Further, an ignition switch signal or the like is input to the control unit 32 from an engine control unit 34 that performs various controls of the engine 10 via a CAN (Controller Area Network) or the like. Then, in the control unit 32, by executing a control program stored in a ROM (Read Only Memory) or the like, as shown in FIG. 3, a heterogeneous discrimination / abnormality determination unit 32A is realized. The control program may be executed not only by the control unit 32 but also by an existing control unit such as the engine control unit 34.

  The different type determination / abnormality determination unit 32A functions as a different type determination unit and an abnormality determination unit. For example, at every predetermined time after the engine is started, it is determined whether there is an erroneous fueling of light oil based on a water level signal from the sensor 30, and an abnormality And a notification signal or a clear signal is output according to the determination and the determination result. The notification signal or the clear signal is input to the erroneous refueling notification unit 36 serving as the first notification unit or the abnormality notification unit 38 serving as the second notification unit, so that the user is notified.

  The misfueling notification means 36 is configured to include, for example, a warning lamp and a buzzer, and turns on the warning lamp in response to the misfueling notification signal and sounds the buzzer to notify the user of misfueling. By sounding the buzzer, for example, when light oil is accidentally put into the reducing agent tank 24 at a gas station or the like, it is possible to immediately notify the user of erroneous fueling. Thereby, it is possible to prevent erroneous oil supply of light oil and to maintain the function of the exhaust purification device.

The abnormality notification unit 38 is configured to include, for example, a warning lamp, and turns on the warning lamp in response to the abnormality notification signal to notify the user of the occurrence of abnormality. Thereby, the user can recognize that some abnormality has occurred in the reducing agent tank 24.
Next, functions related to heterogeneous determination and abnormality determination will be described with reference to the flowchart of FIG.

  The heterogeneous discrimination / abnormality determination unit 32A reads the capacitance type water level signal and the float type water level signal from the sensor 30 in step 1 (abbreviated as “S1” in the figure, the same applies hereinafter). Then, the process proceeds to Step 2 where the water level Lc based on the capacitance type water level signal is subtracted from the water level Ls based on the float type water level signal, and it is determined whether or not the difference value exceeds the first threshold value. The first threshold value is a value for excluding an error range that may occur in the measurement value of the sensor 30 from the different type determination.

As a result of the determination, if the difference value exceeds the first threshold value, the process proceeds to step 3 to determine that light oil has been put into the reducing agent tank 24. A signal is output to operate the misfueling notification means 36 to notify the misfueling.
On the other hand, if the difference value is equal to or smaller than the first threshold value in Step 2, the process proceeds to Step 5, where the water level Ls is subtracted from the water level Lc, and it is determined whether or not the difference value exceeds the second threshold value. . The second threshold value is a value for excluding an error range that may occur in the measurement value of the sensor 30 from the abnormality determination.

As a result of the determination, if the difference value exceeds the second threshold value, the process proceeds to step 6, and some abnormality has occurred in the reducing agent tank 24, such as an increase in pressure in the tank due to breather clogging or the like, or failure of the sensor 30. In step 7, according to the abnormality determination, an abnormality notification signal is output and the abnormality notification means 38 is operated to notify the occurrence of abnormality.
On the other hand, if the difference value is equal to or smaller than the second threshold value in step 5, the process proceeds to step 8 to determine whether the urea aqueous solution is put in the reducing agent tank 24 and return. When normal determination is made, a clear signal is output to both notification means 36 and 38 to stop the notification.

1 is an overall configuration diagram showing an example of an exhaust purification device according to the present invention. The graph explaining the difference in the characteristic of an electrostatic capacitance type water level measurement means and a float type water level measurement means. The block diagram of the function for performing heterogeneous discrimination and abnormality judgment. The flowchart which shows a different kind discrimination | determination and abnormality judgment process.

Explanation of symbols

10 Engine 20 NOx reduction catalyst 24 Reductant tank 30 Sensor 30B Electrode part (capacitance type water level measuring means)
30C float (float type water level measuring means)
32 Control unit 32A Different kind discrimination and abnormality judgment part

Claims (5)

A reducing agent tank for storing a liquid reducing agent or a precursor thereof;
A reduction catalyst for reducing and purifying nitrogen oxides in exhaust using the liquid reducing agent in the reducing agent tank or a precursor thereof; and
Capacitance type water level measuring means for measuring the water level of the liquid in the reducing agent tank from the capacitance between two electrodes hanging parallel to each other in the reducing agent tank;
Float type water level measuring means for measuring the water level of the liquid in the reducing agent tank using a float floating in the liquid in the reducing agent tank;
A different type for determining the different type of liquid in the reducing agent tank based on the difference between the first water level measured by the capacitance type water level measuring means and the second water level measured by the float type water level measuring means. Discrimination means;
An exhaust emission control device for an engine characterized by comprising:   The said different kind discrimination | determination means discriminate | determines the said liquid in a reducing agent tank as a different kind liquid, when the difference value which pulled the said 1st water level from the said 2nd water level exceeds a 1st threshold value. Item 1. An exhaust emission control device for an engine according to Item 1.   The first or second notifying means for notifying that the different liquid has been put into the reducing agent tank when the different kind determining means determines that the different liquid is present. The engine exhaust gas purification apparatus as described.   It further includes an abnormality determining means for determining that an abnormality has occurred in the reducing agent tank when a difference value obtained by subtracting the second water level from the first water level exceeds a second threshold value. The exhaust emission control device for an engine according to any one of claims 1 to 3.   5. The engine exhaust gas purification according to claim 4, further comprising second notification means for notifying that an abnormality has occurred in the reducing agent tank when the abnormality determination means determines that an abnormality has occurred. apparatus.

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