JP4244211B2 - Apparatus and method for measuring liquid reducing agent concentration - Google Patents

Description

  The present invention relates to an exhaust purification device that removes NOx contained in exhaust gas from a diesel engine, a gasoline engine, or the like, and more particularly to a technique for measuring the concentration of a liquid reducing agent in an exhaust purification device that employs selective catalytic reduction (SCR).

  As an exhaust purification device that removes NOx contained in engine exhaust, an exhaust purification device that employs an SCR as disclosed in Patent Document 1 has been proposed. In this exhaust purification device, a reduction catalyst is disposed in the exhaust system, and a reducing agent is injected and supplied upstream of the exhaust of the reducing catalyst to cause a catalytic reduction reaction between NOx in the exhaust and the reducing agent, thereby harming NOx. The component is purified. The reducing agent is stored in a storage tank in a liquid state at room temperature, and a necessary amount corresponding to the engine operating state is injected and supplied from the injection nozzle. The reduction reaction uses ammonia having good reactivity with NOx, and as a reducing agent therefor, an aqueous urea solution or aqueous ammonia solution that easily generates ammonia by hydrolysis with exhaust heat and water vapor in the exhaust. Alternatively, a liquid reducing agent such as HC is used.

  In such an exhaust purification device using a liquid reducing agent, the amount of liquid reducing agent added is controlled in accordance with the engine operating state such as the NOx emission amount and the exhaust temperature, but the concentration of the liquid reducing agent is a specified value. If different (including different solutions such as water and the case where the tank is empty), the reduction reaction on the catalyst will be incomplete, NOx emissions will increase, and unreacted ammonia will be discharged due to excessive supply of ammonia. Is done. Therefore, a concentration measuring device that measures the concentration of liquid reducing agent stored in the tank (referred to as concentration including different solution determination and empty determination) is provided, and a warning to the driver, addition amount control, We are trying to deal with abnormalities such as system shutdown.

This liquid reducing agent concentration measuring apparatus uses a thermal concentration sensor that is installed in a tank of liquid reducing agent and measures the concentration based on heat transfer characteristics between two spaced points.
JP2000-027627

  However, when a thermal concentration sensor is used, there is a problem that due to the measurement principle, if the liquid reducing agent in the tank is shaken due to vibration caused by running, the measurement error becomes large and detection with high accuracy cannot be performed. That is, when convection is generated in the liquid reducing agent due to shaking, the heat transfer characteristic using the reducing agent as a heat transfer medium changes, so that the accuracy of concentration measurement sensitive to the change in the heat transfer characteristic decreases. Therefore, in order to realize measurement in a state where the liquid reducing agent is not shaken, it is considered that the concentration measurement is performed after determining that the vehicle is stopped.

  The present invention has been devised on the basis of such a background, and in order to perform highly accurate concentration measurement, the liquid reducing agent in the tank is as small as possible and the optimal vehicle stop state is determined. Provided are a liquid reducing agent concentration measuring method and apparatus capable of performing the same.

  The most reliable way to say that the liquid reducing agent in the tank is not shaken is when the driver gets into the parked vehicle, turns the ignition key, starts the engine, and starts running. In other words, it can not be said that the liquid reducing agent does not sway in a stopped state that has just stopped from running, such as waiting for a signal, and it is possible that the sway is not settled due to inertia, so the tire is not simply turning. It is not sufficient to determine the stop state. In other words, it is necessary to consider that the shaking of the liquid reducing agent in the tank has stopped after a certain period of time after the vehicle stops, and this can be determined with certainty by the driver on the parked vehicle. It is between getting in and running.

  The present invention based on this finding is a liquid reductant concentration measuring method for an exhaust gas purification apparatus in which a liquid reductant concentration in a tank is measured by a thermal concentration sensor that measures heat transfer characteristics between two spaced points. The measurement by the thermal concentration sensor is performed until the driver gets into the vehicle, starts the engine, and starts running. Examples of methods for detecting the driver's entry include detection of door opening, seat displacement and / or load detection, and detection of cab (driver's cab) displacement caused by the driver's entry when the vehicle is a truck or the like. If these are detected and the concentration measurement is started, the concentration measurement can be completed before the vehicle starts to move.

  According to the present invention as an apparatus for carrying out such a measuring method, in a liquid reducing agent concentration measuring apparatus using a thermosensitive concentration sensor that measures a liquid reducing agent concentration in a tank by a heat transfer characteristic between two spaced points. The control means of the thermal concentration sensor senses the driver's boarding when the engine is stopped, and when the driver's boarding is sensed, the measurement processing operation is started and the liquid reduction by the thermal density sensor is performed. Performing an agent concentration measurement.

The step of detecting the driver's boarding includes, for example, a step of detecting door opening, a step of detecting displacement of the seat, a step of detecting load on the seat, a step of detecting displacement of the cab, or These can be combined.
In this case, in order to ensure measurement accuracy, it is preferable that the number of measurements is as large as possible. Therefore, it is preferable to repeatedly measure the concentration while no vibration is generated, that is, until the engine is started. That is, after the step of measuring the liquid reductant concentration, the engine start may be confirmed, and the step of repeating the liquid reductant concentration measurement by the thermal concentration sensor may be further executed while the engine is not started. The start of the engine can be detected by turning on an ignition switch or the like.

  Furthermore, as an application of the present invention, before the step of writing the engine stop time in the storage means when the engine stops due to turning off the ignition switch or the like, and the step of measuring the liquid reducing agent concentration by the thermal concentration sensor, From the step of reading the immediately preceding engine stop time from the storage means, the step of ending without measuring the liquid reducing agent concentration if a predetermined time has not passed since the read engine stop time, and the read engine stop time The step of measuring the concentration of the liquid reducing agent may be performed if the predetermined time has elapsed. According to this, when the operation of the ignition key is repeated without leaving an interval due to an engine stall or the like, it is possible to cope with the unnecessary density measurement.

  In the present invention, the concentration measurement by the thermal concentration sensor is performed at an optimal timing that it can be said that the liquid reducing agent in the tank is not shaken without vibration and before the driver enters from the parking state and the vehicle starts to move. Execute. That is, it detects the opening of the door, the seat, the cab, etc., predicts that the driver will get in and the vehicle will be used from now on, and measure the concentration at rest before the shaking occurs Yes. Therefore, a highly reliable measurement result is obtained, and the performance of the original exhaust gas purification device is maintained, contributing to NOx emission suppression and ammonia emission prevention.

FIG. 1 shows a schematic diagram of an exhaust emission control device according to the present invention. The illustrated exhaust purification device includes an oxidation catalyst 1, a NOx purification catalyst 2, and an NH ₃ slip catalyst 3 interposed in an exhaust system. An addition device 5 for supplying a suitable amount of the liquid reducing agent to the nozzle 4 has a configuration in which the liquid reducing agent is injected and added from the nozzle 4 into the exhaust gas upstream of the NOx purification catalyst 2. And an ECU (control means) 9 that controls supply of the adding device 5 in accordance with the exhaust temperature by the exhaust temperature sensors 6 and 7, the engine speed obtained from the engine ECU 8, and the like.

  Various liquid reducing agents such as urea water as described above are stored in the tank 10, and a liquid reducing agent concentration measuring device is formed in a position suitable for measurement in the tank 10, in this example, near the bottom of the tank. A thermal density sensor 11 is suspended. The thermosensitive concentration sensor 11 has a base installed outside the upper surface of the tank 10, from which the tip of the sensor hangs down to the bottom of the tank, and is wired from the base to the ECU 9 serving as a control means, with a measurement signal SS. Send.

  In addition to this, the ECU 9 serving as a control means of the concentration measuring device also includes a sensing signal S1 for notifying that the vehicle door 12 is open (including unlocking), and the displacement of the vehicle seat 13 in the vertical and horizontal directions (or the seat). Sense signal S2 that informs the displacement of the cab 14 and a sensing signal S3 that informs the displacement of the cab 14 (cab over type is shown in this example). These sensing signals S1, S2, and S3 are sensed and input to the ECU 9 when the engine is stopped. Any one of the sensing signals S1, S2, and S3 may be set, and it is not necessary to set all the sensing signals. However, for example, when only the door is opened, it can be sensed when the driver gets off, so a system in which the seat displacement is sensed after the door is sensed is also possible. Alternatively, a method of checking whether the ignition switch is turned on after sensing any of the sensing signals S1, S2, S3 can be adopted. In this case, when the ignition switch is turned on, the concentration measurement result that has been measured before that may be stored.

  The ECU 9 is switched off when the engine is stopped according to the information from the engine ECU 8, performs finalization, and waits only with a minimum necessary power supply such as an internal timer. In this engine stop state, any of the detection signals S1, S2, S3 set for the vehicle is input to the ECU 9 in response to any action of the driver opening the door, getting into the cab, or sitting on the seat. This becomes a trigger signal and the ECU 9 is switched on to perform initialization (initialization).

With this initialization, the ECU 9 starts the measurement processing operation, and executes the flow of the liquid reducing agent concentration measurement shown in FIG.
That is, after initialization of the thermal concentration sensor 11 at the start step 20 for initialization, the process proceeds to step 21 where the concentration of the liquid reducing agent is measured by the thermal concentration sensor 11. When the measurement signal SS is obtained by this concentration measurement, the concentration measurement result is output in step 22 by referring to the lookup table of the measurement signal SS and the liquid reducing agent concentration stored in advance in the ROM or the like. In step 23, the data is written in a memory such as a DRAM or an EEPROM provided in the ECU 9 or the adding device 5.

  On the other hand, in this example, in order to perform concentration measurement with higher reliability, concentration measurement is repeated a predetermined number of times while the engine is not started. For this purpose, after step 23 in which the density measurement result is output and written to the memory, in step 24, it is checked whether the ignition switch is on. When the ignition switch is on, the engine has been started, and the process ends without repeating the measurement. In step 24, the engine start may be determined by detecting the engine speed and the fuel injection signal.

  If the ignition switch is not turned on, in step 25, the number of measurements is checked so as not to repeat the number of measurements more than necessary. As a result of this check, if the preset number of times has not been measured, the process returns to step 21 for density measurement, and if the set number has been reached, the process proceeds to step 26 and ends. When the process returns to step 21, the second, third,... Density measurement results that are repeatedly measured are output in step 22 and accumulated in the memory in step 23. Then, the final measurement result can be obtained by finally taking the average.

  The above is a basic example. For example, in the case where the concentration measurement is performed by detecting only door opening, the concentration also reacts to the door opening when the driver gets off the vehicle after driving. It may be possible to carry out the measurement. In view of this, it is possible to store the engine stop time so that the concentration measurement is not performed when the door open detection signal S1 is input immediately after the engine is stopped. This processing flow is shown in FIG.

In the example of FIG. 3, first, as shown in FIG. 3A, the flow starts in step 30 with the ignition key OFF operation, and proceeds to step 31, in which a non-volatile memory such as an EEPROM as a storage means is stored. The current time that is the engine stop time is written, and the process ends at step 32.
Thereafter, in the engine stop state, when the detection signals S1, S2, and S3 are input to the ECU 9 according to any one of the driver's door open, cab entry, and seat seating, the ECU 9 is switched on by the trigger. The measurement processing operation is started in step 33 shown in FIG. In the case of this example, in step 34, the engine stop time immediately before written in the previous step 31 is read and compared with the current time by the internal timer. Or more than 1 hour). If the specified time has not elapsed as a result of this check, the measurement is not performed and the process ends at step 36.

  On the other hand, if the specified time has passed, the process proceeds to step 37, and after the thermal concentration sensor 11 is initialized, the concentration of the liquid reducing agent is measured by the thermal concentration sensor 11. When the measurement signal SS is obtained by this concentration measurement, the concentration measurement result is output in step 38 by referring to the lookup table of the measurement signal SS and the liquid reducing agent concentration, etc., and written in the memory in step 39 as described above. Then, in the same manner as described above, the engine start is checked in step 40, and the number of measurements is checked in step 41. If the preset number of times has not been measured, the process returns to the concentration measurement step 37, If the set number of times has been reached, the routine proceeds to step 42 and ends.

  In this way, by storing the engine stop time and confirming whether or not a predetermined time has passed when the measurement processing operation is started next, it is possible to avoid unnecessary concentration measurement. .

1 is a schematic view of an exhaust purification device according to the present invention. The flowchart explaining an example of the liquid reducing agent density | concentration measurement process which concerns on this invention. The flowchart explaining the other example of the liquid reducing agent density | concentration measurement process which concerns on this invention.

Explanation of symbols

9 ECU (control means)
10 Tank 11 Thermal concentration sensor 12 Door 13 Seat 14 Cab SS Measurement signal S1, S2, S3 Sensing signal

Claims (12)

In a liquid reductant concentration measuring device using a thermal concentration sensor that measures the liquid reductant concentration in a tank by heat transfer characteristics between two spaced points,
The control means of the thermal density sensor is
Detecting the driver's boarding when the engine is stopped;
When the driver's boarding is sensed by this, the measurement processing operation is started and the liquid reducing agent concentration measurement by the thermal concentration sensor is performed,
The liquid reducing agent concentration measuring apparatus characterized by performing.   2. The liquid reducing agent concentration measuring apparatus according to claim 1, wherein the step of detecting the driver's boarding is a step of detecting door opening.   2. The liquid reducing agent concentration measuring apparatus according to claim 1, wherein the step of detecting the driver's boarding is a step of detecting a displacement of the seat.   2. The liquid reducing agent concentration measuring apparatus according to claim 1, wherein the step of detecting the driver's boarding is a step of detecting a load on the seat.   2. The liquid reducing agent concentration measuring apparatus according to claim 1, wherein the step of detecting the driver's boarding is a step of detecting displacement of the cab.   The step of confirming the start of the engine after the step of measuring the liquid reductant concentration, and further executing the step of repeating the liquid reductant concentration measurement by the thermal concentration sensor while the engine is not started is further performed. Item 6. The liquid reducing agent concentration measuring apparatus according to any one of Items 1 to 5. Writing the engine stop time in the storage means when the engine is stopped;
Before the step of measuring the liquid reducing agent concentration by the thermosensitive concentration sensor, reading the previous engine stop time from the storage means;
A step of ending without measuring the liquid reducing agent concentration if a predetermined time has not passed since the read engine stop time; and
Carrying out the liquid reducing agent concentration measurement if a predetermined time or more has passed since the read engine stop time;
The liquid reducing agent concentration measuring apparatus according to any one of claims 1 to 6, wherein: In the method of measuring the liquid reducing agent concentration in the exhaust purification apparatus, wherein the concentration of the liquid reducing agent in the tank is measured by a thermal concentration sensor that measures the heat transfer characteristics between two spaced points.
The liquid reducing agent concentration measuring method, wherein the measurement by the thermal concentration sensor is executed during a period from when the driver gets into the vehicle to start the engine and the vehicle starts running.   9. The liquid reducing agent concentration measuring method according to claim 8, wherein the measurement is started by detecting that the driver has entered the vehicle by opening the door.   10. The liquid reducing agent concentration measuring method according to claim 8, wherein the measurement is started by detecting that the driver has entered the vehicle by the displacement of the seat.   The liquid reducing agent concentration measuring method according to any one of claims 8 to 10, wherein the measurement is started by sensing that the driver has entered the vehicle by a load on the seat.   The liquid reducing agent concentration measuring method according to any one of claims 8 to 11, wherein the measurement is started by sensing that the driver has entered the vehicle by displacement of the cab.

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