JP4869216B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to a technique for sequentially recording a state of consumption of a liquid reducing agent or a precursor thereof in association with a state of fuel consumption in an exhaust purification device that reduces and purifies nitrogen oxide (NOx) in exhaust gas.

The liquid reducing agent or its precursor is injected and supplied upstream of the NOx reduction catalyst disposed in the engine exhaust pipe, and the NOx in the exhaust reacts with the reducing agent in the NOx reduction catalyst to make NOx harmless. Various exhaust purification apparatuses for reducing and purifying have been proposed. In such an exhaust purification device, when a failure such as clogging of the injection nozzle occurs, the reducing agent is not supplied to the NOx reduction catalyst, and thus the required NOx purification rate cannot be obtained. For this reason, the present applicant has proposed a technique for performing failure determination based on the pressure of high-pressure air mixed with a liquid reducing agent or a precursor thereof in Japanese Patent No. 3714559 (Patent Document 1).
Japanese Patent No. 3714559

However, the conventionally proposed technology can be applied to an exhaust gas purification apparatus that injects and supplies high-pressure air mixed with a liquid reducing agent or a precursor thereof. However, the liquid reducing agent or a precursor thereof is directly applied without using high-pressure air. It could not be applied to an exhaust gas purification apparatus that supplies fuel.
Further, when attention is paid to the fact that there is a correlation between the consumption situation of the liquid reducing agent or its precursor and the fuel consumption situation, the presence or absence of a failure can be determined based on the correlation. However, since the consumption status of the liquid reducing agent or its precursor changes depending on, for example, the vehicle travel route, loading status, driving characteristics, etc. May be determined to have occurred even though no failure has occurred. For this reason, in order to improve the failure determination accuracy, it is desirable to sequentially record the consumption state and the fuel consumption state of the liquid reducing agent or its precursor over a long period of time and perform failure determination from the history.

  However, if the consumption status is sequentially recorded at short intervals (time, distance, etc.), the failure determination accuracy is improved, but the storage area becomes enormous, and the memory built in the control unit cannot cover it. For example, an external storage device such as a hard disk drive is required. On the other hand, if the consumption status is sequentially recorded at a long interval, even if the consumption status changes after a certain point due to the occurrence of the failure, it is difficult to clearly show this, so that the occurrence of the failure may be overlooked.

  Therefore, in view of the conventional problems as described above, the present invention sequentially records recent consumption statuses at short intervals, while recording past consumption statuses sequentially at long intervals, which is necessary for recording the consumption status. An object of the present invention is to provide an exhaust emission control device that can ensure failure determination accuracy while reducing the storage area.

  Therefore, according to the first aspect of the present invention, a reduction catalyst that reduces and purifies nitrogen oxides in exhaust gas by a reduction reaction using a reducing agent, a reducing agent tank that stores a liquid reducing agent or a precursor thereof, and the reduction A reducing agent addition device for controlling an addition flow rate for adding a liquid reducing agent stored in an agent tank or a precursor thereof from an injection nozzle disposed upstream of the exhaust of the reduction catalyst, and a hierarchical structure including at least three layers A control unit including a non-volatile memory in which a table area in which a plurality of records including the consumption status of the liquid reducing agent or its precursor and the consumption status of the fuel are recorded is secured, The control unit includes a reducing agent addition process for controlling the reducing agent addition device based on an addition flow rate of a liquid reducing agent or a precursor thereof according to an engine operating state. And a record of the consumption situation of the liquid reducing agent or its precursor and the consumption situation of the fuel during the traveling every time the vehicle travels a predetermined distance, sequentially records in a table of the highest hierarchy When records are recorded to the end of the table of each level except for the processing and the lowest level, the average of the consumption status of the liquid reducing agent or its precursor and the consumption status of the fuel recorded in the table is calculated, and these Are sequentially recorded in the lower hierarchy table, and a second consumption status recording process for resetting the table in which the record has been recorded is executed.

According to a second aspect of the present invention, the control unit sequentially calculates the addition flow rate and the fuel injection flow rate to calculate the consumption state of the liquid reducing agent or its precursor and the consumption state of the fuel during the predetermined distance traveling. It is characterized by that.
According to a third aspect of the present invention, the control unit stores an integrated value storing process in which each integrated value obtained by sequentially integrating the addition flow rate and the fuel injection amount is stored in a nonvolatile memory when the engine is stopped, And an integrated value reading process for reading each integrated value stored in the memory.

According to a fourth aspect of the present invention, the control unit records an average of the consumption situation of the liquid reducing agent or its precursor and the consumption situation of the fuel in the table of the lowest hierarchy in a ring knitting method. .
The invention according to claim 5 is characterized in that the consumption state is a consumption amount or a consumption rate.

  The invention according to claim 6 comprises a water level sensor for measuring the remaining amount of the liquid reducing agent or its precursor in the reducing agent tank, and a monitor capable of displaying at least a numeral, and the control unit has the uppermost level. The consumption status of the liquid reducing agent or its precursor recorded in the first record of the hierarchy table, the remaining amount measured by the water level sensor, and the travelable distance calculated from the consumption status are displayed on the monitor. The display processing is further executed.

  According to the first aspect of the present invention, every time the vehicle travels a predetermined distance, a record including the consumption state of the liquid reducing agent or its precursor and the consumption state of the fuel during the traveling is sequentially stored in the table in the highest hierarchy. To be recorded. When records are recorded up to the end of the table of each layer excluding the lowest layer, the average of the consumption situation of the liquid reducing agent or its precursor recorded in the table and the consumption situation of the fuel is calculated, and these are calculated. In addition to the sequential recording in the lower hierarchy table, the table in which the record is recorded is reset. For this reason, recent consumption statuses are sequentially recorded at short intervals, while past consumption statuses are recorded at intervals that gradually increase as they go back. Therefore, for example, when the consumption of the liquid reducing agent or its precursor is low, it is possible to increase whether or not a failure has occurred in the exhaust gas purification apparatus by referring to the correlation of the consumption status recorded in the table of the highest hierarchy. It can be judged with accuracy. On the other hand, since the past consumption situation is recorded at a long interval, the storage area required for the consumption situation recording is reduced, and it is possible to determine a change with time since the vehicle was manufactured.

According to the second aspect of the present invention, the consumption state of the liquid reducing agent or its precursor and the consumption state of the fuel during the predetermined distance traveling can be calculated by sequentially integrating the addition flow rate and the fuel injection flow rate.
According to the third aspect of the invention, each integrated value obtained by sequentially integrating the addition flow rate and the fuel injection amount when the engine is stopped is stored in the nonvolatile memory, while each integrated value stored in the nonvolatile memory when the engine is started is stored in the nonvolatile memory. Since it is read, it is possible to take over the data from the previous run, and the consumption status in the continuous run can be recorded.

According to the fourth aspect of the present invention, in the ring knitting method, the average of the consumption situation of the liquid reducing agent or its precursor and the consumption situation of the fuel are recorded in the table at the lowest level so that the table does not overflow. Can be.
According to the invention described in claim 5, the consumption amount or the consumption rate can be adopted as the consumption state.

  According to the sixth aspect of the present invention, the consumption state of the liquid reducing agent or its precursor at a predetermined distance traveled recently and the distance traveled by the liquid reducing agent or its precursor remaining in the reducing agent tank are monitored. Therefore, the vehicle driver or the like can easily recognize the operating state of the exhaust emission control device. When the consumption of the liquid reducing agent or its precursor is extremely small or large, it can be determined that some trouble has occurred in the exhaust gas purification device. For example, when the vehicle is brought into a repair shop and inspected, nitrogen is removed. Traveling in a state where oxides are not sufficiently purified can be suppressed.

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) into 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, a NOx reduction catalyst 20 for reducing and purifying NOx using ammonia generated from an aqueous urea solution, and an ammonia oxidation catalyst 22 for oxidizing ammonia that has passed through the NOx reduction catalyst 20 are provided. Is done. On the other hand, the urea aqueous solution stored in the reducing agent tank 24 is supplied to the injection nozzle 18 while the addition flow rate is controlled by the reducing agent addition device 26.

  As a control system of the exhaust purification apparatus, a temperature sensor 28 for measuring the exhaust temperature as an engine operating state is disposed in the exhaust pipe 14 positioned between the nitrogen oxidation catalyst 16 and the injection nozzle 18 and a reducing agent. The tank 24 is provided with a water level sensor 30 for measuring the remaining amount of the urea aqueous solution. A transmission (not shown) connected to the engine 10 is provided with a vehicle speed sensor 32 that measures the vehicle speed from the rotational speed of its output shaft. Each measurement signal from the temperature sensor 28, the water level sensor 30 and the vehicle speed sensor 32 is input to a control unit 34 incorporating a computer. The control unit 34 is connected to an engine control unit 36 that electronically controls the engine 10 via a network such as a CAN (Controller Area Network), and reads a fuel injection flow rate, an engine rotation speed, and the like as an engine operation state at an arbitrary time point. Be able to.

  Then, the control unit 34 executes a control program written in the ROM (Read Only Memory) or the like to electronically control the reducing agent adding device 26, and also an EEPROM (Electrically Erasable Programmable Read Only) as a nonvolatile memory. Record the urea aqueous solution and fuel consumption rates in Memory. In addition, the control unit 34 displays the consumption rate of the urea aqueous solution and the travel distance traveled by the urea aqueous solution remaining in the reducing agent tank 24 on a monitor 38 such as a liquid crystal capable of displaying at least numbers.

The control unit 34 executes a reducing agent addition process, a first consumption status recording process, a second consumption status recording process, an integrated value storage process, an integrated value reading process, and a display process, respectively, according to the control program.
Here, the EEPROM of the control unit 34 has a table structure in which a plurality of records including the consumption state of the urea aqueous solution and the consumption state of the fuel are recorded while forming a hierarchical structure including at least three layers. Specifically, as shown in FIG. 2A, the EEPROM records a record consisting of a travel distance X [km], a reducing agent consumption Y [L], and a fuel consumption Z [L]. Table A and Table A in which l, m, and n records each comprising a reducing agent consumption rate [km / L] and a fuel consumption rate [km / L] are recorded as shown in FIGS. The area of ~ C is secured. Note that table A corresponds to the table in the highest hierarchy, and table C corresponds to the table in the lowest hierarchy. The records in the work table and the tables A to C are each set to 0 when the vehicle is manufactured, and the variables i, j and k indicating the records in the tables A to C are respectively set to 0 when the vehicle is manufactured. In addition, it is assumed to be backed up by a known technique so that the content does not change even if the power supply is cut off.

In such an exhaust purification apparatus, the urea aqueous solution injected and supplied from the injection nozzle 18 to the exhaust pipe 14 is hydrolyzed using exhaust heat and water vapor in the exhaust to produce ammonia. It is known that the produced ammonia undergoes a reduction reaction 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 rate in the NOx reduction catalyst 20, NO is oxidized to NO ₂ by the nitrogen oxidation catalyst 16, and the ratio of NO and NO ₂ in the exhaust gas is improved to be suitable for the reduction reaction. 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 can be prevented from being released into the atmosphere as it is.

FIG. 3 shows a reducing agent addition process that is repeatedly executed at predetermined time intervals in the control unit 34 when the engine is started.
In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the exhaust temperature is read from the temperature sensor 28, and the fuel injection flow rate and the engine speed are read from the engine control unit 36.

In step 2, a control map that defines the reducing agent addition flow rate is referred to, and a reducing agent addition flow rate suitable for the exhaust gas temperature, the fuel injection flow rate, and the engine speed is calculated.
In step 3, a control signal corresponding to the reducing agent addition flow rate is output to the reducing agent addition device 26.
According to the reducing agent addition process, the reducing agent addition device 26 is controlled in accordance with the exhaust temperature, the fuel injection flow rate, and the engine rotation speed, and the urea aqueous solution required for reducing and purifying NOx in the exhaust is reduced in the NOx reduction catalyst 20. Injected and supplied upstream of exhaust. Then, through the process described above, NOx in the exhaust is reduced and purified.

FIG. 4 shows a consumption status recording process executed by the control unit 34 when the engine is started.
In step 11, work tables and tables A to C are read from the EEPROM into a RAM (Random Access Memory).
In step 12, it is determined whether or not the reducing agent consumption rate is recorded in the record A [0] of the table A, that is, whether or not the reducing agent consumption rate of the record A [0] is not zero. If the reducing agent consumption rate is recorded in the record A [0], the process proceeds to step 13 (Yes), while if the reducing agent consumption rate is not recorded in the record A [0], the process proceeds to step 18 ( No).

In step 13, the remaining amount of urea aqueous solution is read from the water level sensor 30.
In step 14, the remaining distance of the urea aqueous solution is multiplied by the reducing agent consumption rate of the record A [0] to calculate the distance (travelable distance) that can be traveled by the urea aqueous solution remaining in the reducing agent tank 24.
In step 15, the reducing agent consumption rate and the travelable distance are displayed on the monitor 38.

In step 16, it is determined whether or not the ignition is turned off to stop the engine 10. If the ignition is turned off, the process proceeds to step 17 (Yes), while if the ignition remains on, the process proceeds to step 18 (No).
In step 17, the working tables and tables A to C on the RAM are written in the EEPROM.

In step 18, a subroutine for performing the consumption status update process is called in order to update the tables A to C as appropriate, and then the process returns to step 12.
5 and 6 show the consumption status update process as a subroutine.
In step 21, the vehicle speed is read from the vehicle speed sensor 32 and the fuel injection flow rate is read from the engine control unit 36.

In step 22, the travel distance X is updated by sequentially integrating the vehicle speed, and the reducing agent consumption amount Y and the fuel consumption amount Z are updated by sequentially integrating the reducing agent addition flow rate and the fuel injection flow rate, respectively. Here, the reducing agent addition flow rate is the one calculated in step 2 of FIG.
In step 23, it is determined whether or not the travel distance X has become a predetermined distance (for example, 200 km) or more. If the travel distance X is equal to or greater than the predetermined distance, the process proceeds to step 24 (Yes), while if the travel distance X is less than the predetermined distance, the process returns to the main routine (No).

In step 24, the travel distance X is divided by the reducing agent consumption amount Y and the fuel consumption amount Z, respectively, thereby calculating the reducing agent consumption rate and the fuel consumption rate indicating the distance traveled by the urea aqueous solution and fuel per unit volume. To do.
In step 25, the reducing agent consumption rate and the fuel consumption rate are recorded in the record A [i] of the table A.

In step 26, the variable i is incremented.
In step 27, it is determined whether or not the variable i is larger than l indicating the last record of the table A. If the variable i becomes larger than l, the process proceeds to step 28 (Yes), while if the variable i is equal to or smaller than l, the process returns to the main routine (No).
In step 28, the variable i is reset to zero.

In step 29, the average of the reducing agent consumption rate and the fuel consumption rate is calculated from the records A [0] to A [l] of the table A.
In step 30, the average of the reducing agent consumption rate and the fuel consumption rate is recorded in the record B [j] of the table B.
In step 31, the records A [0] to A [l] of the table A are reset to the initial state.

In step 32, the variable j is incremented.
In step 33, it is determined whether or not the variable j is larger than m indicating the last record of the table B. If the variable j is greater than m, the process proceeds to step 34 (Yes), while if the variable j is equal to or less than m, the process returns to the main routine (No).
In step 34, the variable j is reset to zero.

In step 35, the average of the reducing agent consumption rate and the fuel consumption rate is calculated from the records B [0] to B [m] of the table B.
In step 36, the average of the reducing agent consumption rate and the fuel consumption rate is recorded in the record C [k] of the table C.
In step 37, the records B [0] to B [m] of the table B are reset to the initial state.

In step 38, the variable k is incremented.
In step 39, it is determined whether or not the variable k is larger than n indicating the last record of the table C. If the variable k is larger than n, the process proceeds to step 40 (Yes), while if the variable k is n or less, the process returns to the main routine (No).
In step 40, the variable k is reset to zero. That is, the average of the reducing agent consumption rate and the fuel consumption rate is recorded in the table C by the ring knitting method, so that the table C does not overflow.

  According to such an exhaust purification device, the reducing agent consumption rate and the fuel consumption rate are sequentially recorded in the records A [0] to A [l] of the table A every time the vehicle travels a predetermined distance. When the consumption rate is recorded up to the record A [l] of the table A, the average of the reducing agent consumption rate and the fuel consumption rate recorded in the records A [0] to A [l] is calculated. Are sequentially recorded in the records B [0] to B [m]. When the consumption rate is recorded up to the record B [m] in the table B, the average of the reducing agent consumption rate and the fuel consumption rate recorded in the records B [0] to B [m] is calculated. Are sequentially recorded in the records C [0] to C [n]. That is, the consumption state when traveling [predetermined distance] in table A, the consumption state when traveling [predetermined distance × l] in table B, and the traveling state in [predetermined distance × l × m] in table C Each consumption situation is recorded. For this reason, recent consumption statuses are sequentially recorded at short intervals, while past consumption statuses are recorded at intervals that gradually increase as they go back.

  Therefore, for example, when the consumption of the urea aqueous solution is small, the exhaust purification device is referred to by referring to the correlation between the reducing agent consumption rate and the fuel consumption rate recorded in the records A [0] to A [l] of Table A. Whether or not a failure has occurred can be determined with high accuracy. On the other hand, since the past reducing agent consumption rate and fuel consumption rate are recorded at long intervals, the storage area required for recording the consumption status is reduced, and it is possible to determine the change with time since the vehicle was manufactured.

  Further, since the reducing agent consumption rate at the predetermined distance traveled recently and the travelable distance calculated therefrom are displayed on the monitor 38, the vehicle driver or the like can easily recognize the operating state of the exhaust gas purification device. . That is, when the reducing agent consumption rate shows an extremely small or large value, it can be determined that some trouble has occurred in the exhaust gas purification device. For example, by bringing the vehicle to a repair shop and inspecting it, Traveling in a state where NOx purification by the purification device is not sufficiently performed can be suppressed.

  In addition, when the engine is stopped, the travel distance X, the reducing agent consumption amount Y, and the fuel consumption amount Z are saved in the EEPROM, while these are read out when the engine is started. It is possible to record the consumption status during driving. Since various data is written into the EEPROM only when the engine is stopped, even if the EEPROM can be erased and rewritten only several tens to million times, it is possible to prevent the lifetime from being exhausted immediately.

  Note that, depending on the EEPROM capacity of the control unit 34, the reducing agent consumption rate and the fuel consumption rate may be sequentially recorded using four or more tables. Further, the consumption state of the reducing agent and the fuel is not limited to the consumption rate, and a consumption amount may be adopted. Furthermore, the liquid reducing agent or its precursor is not limited to an aqueous urea solution, and may be an aqueous ammonia solution, a light oil containing hydrocarbon as a main component, or the like.

1 is an overall configuration diagram showing an embodiment of an exhaust emission control device according to the present invention. The data structure recorded on EEPROM is shown, (A) is explanatory drawing of a table for work, (B)-(D) is explanatory drawing of table AC of the hierarchical structure which records a consumption condition. Flow chart showing reducing agent addition process Flow chart showing main routine of consumption status recording process Flow chart showing a subroutine of consumption status recording processing Flow chart showing a subroutine of consumption status recording processing

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 18 Injection nozzle 20 NOx reduction catalyst 24 Reductant tank 26 Reductant addition apparatus 28 Temperature sensor 30 Water level sensor 32 Vehicle speed sensor 34 Control unit 36 Engine control unit 38 Monitor

Claims (6)

A reduction catalyst for reducing and purifying nitrogen oxides in exhaust gas by a reduction reaction using a reducing agent;
A reducing agent tank for storing a liquid reducing agent or a precursor thereof;
A reducing agent addition device for controlling an addition flow rate of adding the liquid reducing agent stored in the reducing agent tank or a precursor thereof from an injection nozzle disposed upstream of the exhaust of the reduction catalyst;
Control unit comprising a non-volatile memory in which a table area in which a plurality of records including a consumption state of a liquid reducing agent or its precursor and a consumption state of fuel are recorded is ensured while having a hierarchical structure including at least three layers When,
Comprising
The control unit is
A reducing agent addition process for controlling the reducing agent addition device based on an addition flow rate of a liquid reducing agent or a precursor thereof according to an engine operating state;
A first consumption state recording process for sequentially recording a record including a consumption state of a liquid reducing agent or a precursor thereof and a consumption state of a fuel during the traveling of the vehicle every predetermined distance in a table in the highest hierarchy. ,
When records are recorded up to the end of the table of each hierarchy excluding the lowest hierarchy, the average of the consumption situation of the liquid reducing agent or its precursor and the fuel consumption situation recorded in the table is calculated, A second consumption status recording process for sequentially recording the table in the hierarchy and resetting the table in which the record has been recorded;
Exhaust gas purification apparatus characterized by performing.   2. The control unit according to claim 1, wherein the control unit sequentially accumulates the addition flow rate and the fuel injection flow rate to calculate a consumption state of the liquid reducing agent or its precursor and a consumption state of the fuel during the predetermined distance traveling. The exhaust emission control device described. The control unit is
Integrated value storage processing for storing each integrated value obtained by sequentially integrating the addition flow rate and the fuel injection amount in a nonvolatile memory when the engine is stopped;
An integrated value reading process for reading each integrated value stored in the non-volatile memory when the engine is started;
The exhaust emission control device according to claim 2, further comprising:   4. The control unit according to claim 1, wherein the control unit records an average consumption state of the liquid reducing agent or a precursor thereof and an consumption state of the fuel in the table of the lowest hierarchy in a ring knitting method. The exhaust emission control device according to any one of the above.   The exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the consumption state is a consumption amount or a consumption rate. A water level sensor for measuring the remaining amount of the liquid reducing agent or its precursor in the reducing agent tank;
A monitor that can display at least numbers,
With
The control unit is capable of running calculated from the consumption status of the liquid reducing agent or its precursor recorded in the first record of the top-level table, the remaining amount measured by the water level sensor, and the consumption status. The exhaust emission control device according to any one of claims 1 to 5, further comprising a display process of displaying the distance on a monitor.

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