JP2019070351A - Abnormality diagnostic device for exhaust emission control device for internal combustion engine - Google Patents

Abstract

To improve diagnosis accuracy when diagnosing abnormality of supply of a reducing agent.SOLUTION: An abnormality diagnostic device for an exhaust emission control device for an internal combustion engine includes: a determination section for determining that a condition of execution of abnormality diagnosis is satisfied when a vehicle is stopped; and a diagnosis section for executing the abnormality diagnosis on the basis of a pressure reduction amount of a reducing agent detected by a pressure detector when the reducing agent is supplied from the addition valve in the case where the determination section determines that the condition of execution of the abnormality diagnosis is satisfied.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an abnormality diagnosis device for an exhaust gas purification device for an internal combustion engine.

  A selective reduction type NOx catalyst (hereinafter simply referred to as “NOx catalyst”) is known which purifies NOx contained in exhaust gas from an internal combustion engine by using ammonia as a reducing agent. On the upstream side of the NOx catalyst, an addition valve or the like for adding ammonia or a precursor of ammonia to the exhaust gas is installed. As a precursor of ammonia, urea can be exemplified. Hereinafter, a precursor of ammonia or ammonia is collectively referred to as a "reductant".

  When the reducing agent is supplied from the addition valve, feedback control is performed based on the rotational speed of a pump that discharges the reducing agent. Here, the feedback control is stopped while maintaining the rotational speed of the pump constant, and based on the amount of pressure drop in the reducing agent passage when the reducing agent is supplied, abnormality diagnosis of the reducing agent supply device The technique which implements is known (for example, refer patent document 1).

US Patent Application Publication No. 2015/104363

  During traveling of the vehicle, the traveling vibration may deform the reducing agent passage, and the reducing agent pressure in the reducing agent passage may change. Since the change in the reducing agent pressure affects the pressure in the reducing agent passage when the reducing agent is supplied, if the abnormality diagnosis of the reducing agent supply device is performed based on the pressure, there is a possibility of a misdiagnosis.

  The present invention has been made in view of the above-described problems, and an object thereof is to improve the diagnostic accuracy when diagnosing the supply abnormality of the reducing agent.

  One aspect of the present invention is a catalyst provided in an exhaust passage of an internal combustion engine mounted on a vehicle and purifying exhaust gas using a reducing agent, an addition valve for supplying the reducing agent to the catalyst, and discharging the reducing agent Cleaning of an internal combustion engine comprising a pump, a reducing agent passage connecting the pump and the addition valve to circulate the reducing agent, and a pressure detecting device detecting the pressure of the reducing agent in the reducing agent passage An abnormality diagnosis apparatus for an exhaust gas purification apparatus for an internal combustion engine, which is an apparatus for carrying out an abnormality diagnosis for the apparatus, comprising: a determination unit that determines that the condition for carrying out the abnormality diagnosis is established when the vehicle is stopped; According to the pressure drop amount of the reducing agent detected by the pressure detecting device when the reducing agent is supplied from the addition valve when it is determined that the condition for performing the abnormality diagnosis is satisfied by the determination unit. Based on the above A diagnosis unit for performing the normal diagnosis, abnormality diagnosis device for an exhaust gas purification system for an internal combustion engine having a.

  According to the present invention, it is possible to improve the diagnostic accuracy when diagnosing the supply abnormality of the reducing agent.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake system and exhaust system. It is the figure which showed the relationship between the average acceleration (horizontal axis) of a reducing agent channel, and the change amount (vertical axis) of the reducing agent pressure detected by the pressure sensor. It is the time chart which showed transition of the vehicle speed at the time of performing abnormality diagnosis of a reducing agent supply device, the switching state of an addition valve, and reducing agent pressure. It is the flowchart which showed the flow which judges whether abnormality diagnosis of the reducing agent supply device concerning an example is carried out. It is the flowchart which showed the flow of abnormality diagnosis of the reducing agent supply device.

  Hereinafter, with reference to the drawings, modes for carrying out the present invention will be exemplarily described in detail based on examples. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention to them unless otherwise specified.

(Example)
FIG. 1 is a view showing a schematic configuration of an internal combustion engine according to the present embodiment and an intake system and an exhaust system thereof. The internal combustion engine 1 is a diesel engine mounted on a vehicle 100. However, the internal combustion engine 1 may be a gasoline engine. An exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is provided with a selective reduction type NOx catalyst 3 (hereinafter referred to as “NOx catalyst 3”) that selectively reduces NOx in the exhaust gas using ammonia as a reducing agent.

  In the exhaust passage 2 upstream of the NOx catalyst 3, a reducing agent supply device 4 for supplying a reducing agent to the NOx catalyst 3 is provided. The reducing agent supply device 4 includes a tank 41, an addition valve 42, a reducing agent passage 43, a pump 44, a pressure sensor 45, a return passage 47, and a check valve 48.

  The tank 41 stores urea water. The addition valve 42 is attached to the exhaust passage 2 upstream of the NOx catalyst 3 to inject urea water. The reducing agent passage 43 connects the tank 41 and the addition valve 42 to circulate urea water. The urea water supplied from the addition valve 42 is hydrolyzed by the heat of the exhaust gas or the heat from the NOx catalyst 3 to be ammonia, and is adsorbed to the NOx catalyst 3. This ammonia is used as a reducing agent in the NOx catalyst 3. In the following, ammonia and urea water are collectively referred to as a reducing agent.

  The pump 44 is provided at a position where the reducing agent passage 43 is connected to the tank 41 and discharges the reducing agent. The pump 44 may be installed in the tank 41. The pump 44 is an electric pump and rotates by supplying electric power. The pump 44 can change the discharge amount of the reducing agent by changing the rotational speed. Thereby, the pressure of the reducing agent can be adjusted.

  Further, the reducing agent passage 43 is provided with a pressure sensor 45 for detecting the pressure of the reducing agent. In the present embodiment, the pressure sensor 45 corresponds to the pressure detection device in the present invention. The pump 44 is provided with a pump rotational speed sensor 46 that detects the rotational speed of the pump 44 (which may be the number of rotations per minute). Further, the return passage 47 connects the reducing agent passage 43 and the tank 41. The return passage 47 is a passage for returning the reducing agent out of the reducing agent discharged from the pump 44 to the tank 41 via the check valve 48 in an amount that exceeds a certain pressure. The check valve 48 is provided in the return passage 47, and opens at a constant pressure to flow the reducing agent from the reducing agent passage 43 to the tank 41 side.

Further, upstream of the addition valve 42, an upstream NOx sensor 11 is provided which detects the concentration of NOx in the exhaust flowing into the NOx catalyst 3. Further, downstream of the NOx catalyst 3, a downstream NOx sensor 12 for detecting NOx concentration in the exhaust flowing out of the NOx catalyst 3, and a temperature sensor 13 for detecting exhaust temperature are provided.

  Further, an intake passage 6 is connected to the internal combustion engine 1. A throttle 7 for adjusting the amount of intake air of the internal combustion engine 1 is provided in the middle of the intake passage 6. Further, an air flow meter 16 for detecting the amount of intake air of the internal combustion engine 1 is attached to the intake passage 6 upstream of the throttle 7. In addition, the vehicle 100 is provided with a vehicle speed sensor 17 that detects the speed of the vehicle 100.

  The internal combustion engine 1 is provided with an ECU 10 which is an electronic control unit. The ECU 10 controls the operating state of the internal combustion engine 1, the exhaust gas purification device, and the like. In addition to the upstream NOx sensor 11, the downstream NOx sensor 12, the temperature sensor 13, the air flow meter 16, the vehicle speed sensor 17, the pressure sensor 45, the pump rotational speed sensor 46, the crank position sensor 14 and the accelerator opening The sensors 15 are electrically connected, and the output value of each sensor is passed to the ECU 10.

  The ECU 10 can grasp the operating state of the internal combustion engine 1 such as the engine rotational speed based on the detection of the crank position sensor 14 and the engine load based on the detection of the accelerator opening degree sensor 15. In the present embodiment, NOx in the exhaust flowing into the NOx catalyst 3 can be detected by the upstream side NOx sensor 11, but the exhaust emitted from the internal combustion engine 1 (exhaust before being purified by the NOx catalyst 3) That is, since the NOx contained in the exhaust flowing into the NOx catalyst 3 has relevance to the operating state of the internal combustion engine 1, it can also be estimated based on the operating state of the internal combustion engine 1. Further, the ECU 10 can estimate the temperature of the NOx catalyst 3 based on the exhaust temperature detected by the temperature sensor 13. Further, it is also possible to estimate the temperature of the NOx catalyst 3 based on the operating state of the internal combustion engine 1. On the other hand, the throttle 7, the addition valve 42, and the pump 44 are connected to the ECU 10 through electrical wiring, and these devices are controlled by the ECU 10.

  Then, while the internal combustion engine 1 is in operation, the ECU 10 performs reducing agent supply control, which is control for supplying a reducing agent to the NOx catalyst 3 in order to reduce NOx in the exhaust passing through the NOx catalyst 3. In the reducing agent supply control, the reducing agent is supplied from the adding valve 42 into the exhaust gas by operating the pump 44 and opening the adding valve 42. At this time, the ECU 10 supplies a reducing agent from the addition valve 42 so that the ammonia adsorption amount of the NOx catalyst 3 becomes the target value of the ammonia adsorption amount of the NOx catalyst 3 (hereinafter, also referred to as target adsorption amount). At this time, the ECU 10 is consumed to purify NOx in the NOx catalyst 3 during a period from the previous supply start point of the reducing agent to the current supply start point of the reducing agent (hereinafter, also referred to as supply interval). The NOx catalyst is supplemented by compensating for the amount of ammonia (hereinafter also referred to as ammonia consumption) and the amount of ammonia desorbed from the NOx catalyst 3 and reduced without purifying NOx (hereinafter referred to as ammonia desorption amount). The amount of reducing agent supplied from the addition valve 42 (hereinafter, also referred to as reducing agent supply amount) is calculated so that the ammonia adsorption amount of 3 becomes the target adsorption amount.

Therefore, the ECU 10 is based on the amount of NOx flowing into the NOx catalyst 3 (hereinafter, also referred to as inflow NOx amount), the temperature of the NOx catalyst 3 (hereinafter, also referred to as catalyst temperature), and the target adsorption amount in the NOx catalyst 3 The reducing agent supply amount is repeatedly calculated for each of a plurality of calculation cycles included in the supply interval, and the reducing agent supply amount calculated during the supply interval is integrated. Then, the integrated value of the reducing agent supply amount at the start of the reducing agent supply becomes the command value supplied from the ECU 10 to the addition valve 42. The command value of the reducing agent supply amount is the amount of reducing agent to be actually supplied from the addition valve 42. Since there is a correlation between the reducing agent supply amount, the valve opening time of the addition valve 42, and the pressure of the reducing agent, the calculated reducing agent supply amount and the reducing agent can be obtained by obtaining the relationship in advance by experiment or simulation. The valve opening time of the addition valve 42 can be determined from the reducing agent pressure. The ECU 10 supplies the reducing agent by opening the addition valve 42 for a time corresponding to the reducing agent supply amount. The supply of the reducing agent is carried out at predetermined intervals.

  Further, the ECU 10 performs feedback control of the rotational speed of the pump 44 so that the pressure in the reducing agent passage 43 approaches a predetermined pressure. The predetermined pressure is the pressure of a reducing agent suitable for supplying the reducing agent from the addition valve 42. When the reducing agent is supplied from the adding valve 42, the pressure in the reducing agent passage 43 decreases. When a pressure drop in the reducing agent passage 43 is detected by the pressure sensor 45, the rotational speed of the pump 44 is increased to rapidly increase the pressure in the reducing agent passage 43.

  Further, the ECU 10 diagnoses the abnormality of the reducing agent supply device 4 by comparing the amount of pressure reduction of the reducing agent at the time of supplying the reducing agent with the predetermined amount of reduction. The pressure reduction amount of the reducing agent at the time of supplying the reducing agent is a period in which the reducing agent is supplied (may be a period in which the addition valve 42 is open) from the detection value of the pressure sensor 45 at the start of the reducing agent supply. It is calculated by subtracting the minimum value of the detection value of the pressure sensor 45. Further, the predetermined reduction amount is obtained in advance as a pressure reduction amount when the reducing agent supply device 4 is normal, by experiment, simulation or the like.

  Here, when the addition valve 42 and the reducing agent passage 43 are not clogged and the reducing agent is normally supplied from the addition valve 42, the reducing agent is supplied from the addition valve 42 so that the inside of the reducing agent passage 43 is The pressure drops. The amount of pressure reduction of the reducing agent is correlated with the amount of reducing agent supplied from the adding valve 42. Therefore, when the adding valve 42 or the reducing agent passage 43 is clogged, the reducing agent injected from the adding valve 42 As the amount of H decreases, the pressure drop of the reducing agent also decreases. Therefore, if the pressure reduction amount when the reducing agent supply device 4 is normal is set as the predetermined reduction amount, the abnormality of the reducing agent supply device 4 can be obtained by comparing the actual pressure reduction amount with the predetermined reduction amount. Diagnosis is possible. If the pressure reduction amount detected by the pressure sensor 45 is equal to or more than the predetermined reduction amount, the ECU 10 determines that the reducing agent supply device 4 is normal, and the pressure reduction amount detected by the pressure sensor 45 is less than the predetermined reduction amount If so, it is determined that the reducing agent supply device 4 is abnormal.

  By the way, when the vehicle 100 travels, traveling vibration occurs, and the traveling vibration is also transmitted to the reducing agent supply device 4, so that each member constituting the reducing agent supply device 4 also vibrates. For example, when the reducing agent passage 43 is deformed by vibration, the pressure of the reducing agent is affected, so that the detection value of the pressure sensor 45 fluctuates. As described above, if the abnormality diagnosis of the reducing agent supply device 4 is performed based on the detected value of the pressure sensor 45 that has fluctuated, there is a possibility that a misdiagnosis may occur.

  FIG. 2 is a diagram showing the relationship between the average acceleration (horizontal axis) of the reducing agent passage 43 and the amount of change in the reducing agent pressure (vertical axis) detected by the pressure sensor 45. The average acceleration is a value obtained by averaging the absolute values of the acceleration generated in one cycle of the vibration when the reducing agent passage 43 vibrates. The amount of change in the reducing agent pressure is the difference between the maximum value and the minimum value when the reducing agent pressure fluctuates. The larger the average acceleration, the larger the traveling vibration. Thus, as the average acceleration increases, the amount of change in the reducing agent pressure also increases. Then, when the amount of change in the reducing agent pressure increases, the amount of change in the pressure drop of the reducing agent at the time of supplying the reducing agent also increases, so the possibility of erroneous diagnosis also increases. On the other hand, when the vehicle 100 is stopped, the amount of change in the reducing agent pressure is relatively small. Therefore, in the present embodiment, when the vehicle 100 is stopped, the fluctuation of the reducing agent pressure due to the vibration of the reducing agent passage 43 is small, and the abnormality diagnosis of the reducing agent supply device 4 is performed. When the vehicle is traveling, the abnormality diagnosis of the reducing agent supply device 4 is stopped.

FIG. 3 is a time chart showing the transition of the vehicle speed, the open / close state of the addition valve 42, and the reducing agent pressure when the abnormality diagnosis of the reducing agent supply device 4 is performed. The vehicle speed becomes 0 at T1 (the vehicle 100 stops), and the addition valve 42 is opened so as to supply the reducing agent to perform an abnormality diagnosis of the reducing agent supply device 4 at T2. By opening the addition valve 42 at T2, the reducing agent pressure decreases from T2. Then, when the addition valve 42 is closed at T3 and the supply of the reducing agent is stopped, the reducing agent pressure is returned to the original because the pump 44 discharges the reducing agent.

  The ECU 10 reduces the pressure of the reducing agent by subtracting the minimum value of the reducing agent pressure during the period in which the addition valve 42 is open (that is, the period from T2 to T3) from the reducing agent pressure at the reducing agent supply start time T2. By calculating the amount and comparing this amount of pressure reduction with a predetermined amount of reduction, the abnormality determination of the reducing agent supply device 4 is carried out. Note that, instead of the minimum value of the reducing agent pressure during the period in which the addition valve 42 is open, the reducing agent pressure at the time when a predetermined time has elapsed from the reducing agent supply start time T2 may be used. The predetermined time has elapsed at any time during the period from T2 to T3. Further, when calculating the pressure drop amount of the reducing agent, instead of the reducing agent pressure at the reducing agent supply start point T2, any time period from the stop point T1 of the vehicle 100 to the reducing agent supply start point T2 The reductant pressure at may be used.

  FIG. 4 is a flow chart showing a flow of determining whether or not to perform abnormality diagnosis of the reducing agent supply device 4 according to the present embodiment. The flowchart is implemented by the ECU 10 at a predetermined timing. The predetermined timing may be timing for performing an abnormality diagnosis of the reducing agent supply device 4.

  In step S101, it is determined whether the vehicle 100 is stopping. For example, it is determined that the vehicle 100 is stopped when the vehicle speed detected by the vehicle speed sensor 17 is 0, and determined that the vehicle 100 is traveling when the vehicle speed detected by the vehicle speed sensor 17 is greater than 0. Be done. When the rotational speed of the internal combustion engine 1 is a rotational speed corresponding to idle operation, the vehicle 100 may be considered to be at a stop. If an affirmative determination is made in step S101, the process proceeds to step S102.

  In step S102, reductant supply for abnormality diagnosis of the reductant supply device 4 is performed. The reducing agent supply for abnormality diagnosis is performed so as to supply an amount of reducing agent suitable for the abnormality diagnosis of the reducing agent supply device 4. However, the reducing agent supply may be carried out as a matter of course by the reducing agent supply control for supplying the reducing agent to the NOx catalyst 3 in order to reduce the NOx in the exhaust passing through the NOx catalyst 3. When the reducing agent is supplied according to step S102, the feedback control of the rotational speed of the pump 44 may be stopped so that the pressure in the reducing agent passage 43 approaches the predetermined pressure. Then, the pressure drop at the time of supplying the reducing agent appears more significantly, so that the accuracy of the abnormality diagnosis can be improved.

  In step S103, parameters necessary for diagnosing abnormality of the reducing agent supply device 4 are calculated. The ECU 10 calculates the minimum value of the reducing agent pressure during the reducing agent supply period based on the detection value of the pressure sensor 45 during the reducing agent supply period (the period during which the addition valve 42 is open). The reducing agent pressure at the reducing agent supply start time, the pressure reduction amount of the reducing agent in the period in which the reducing agent is supplied, and the like are calculated.

  In step S104, an abnormality diagnosis of the reducing agent supply device 4 is performed. The abnormality diagnosis of the reducing agent supply device 4 will be described based on FIG. 5 described later. On the other hand, when negative determination is made by step S101, it progresses to step S105 and abnormality diagnosis of the reducing agent supply apparatus 4 is stopped. In the present embodiment, the ECU 10 processes step S101 to function as a determination unit in the present invention.

FIG. 5 is a flowchart showing a flow of abnormality diagnosis of the reducing agent supply device 4. The flowchart is executed by the ECU 10. In the present embodiment, the ECU 10 processes the flowchart shown in FIG. 5 to function as a diagnosis unit in the present invention.

  In step S201, it is determined whether the pressure reduction amount of the reducing agent during the period in which the reducing agent calculated in step S103 is supplied is equal to or more than a predetermined reduction amount. That is, in step S201, it is determined whether or not the reducing agent is normally supplied. When an affirmation determination is made by step S201, it progresses to step S202 and it is determined that the reducing agent supply apparatus 4 is normal. On the other hand, when negative determination is made by step S201, it progresses to step S203 and it is determined that the reducing agent supply apparatus 4 is abnormal.

  In this way, when the vehicle 100 is traveling, the abnormality diagnosis of the reducing agent supply device 4 is stopped, so that it is possible to suppress the occurrence of an erroneous diagnosis under the influence of traveling vibration. That is, according to the present embodiment, the accuracy of the abnormality diagnosis of the reducing agent supply device 4 can be improved.

  In the present embodiment, although the selective reduction type NOx catalyst has been described as an example, the abnormality diagnosis of the reducing agent supply device 4 in another catalyst (for example, the storage reduction type NOx catalyst) that purifies the exhaust using the reducing agent The same can be considered in the case of implementing. As the reducing agent, one other than urea water and ammonia can also be used.

1 internal combustion engine 2 exhaust passage 3 selective reduction type NOx catalyst 4 reducing agent supply device 6 intake passage 7 throttle 10 ECU
11 upstream NOx sensor 12 downstream NOx sensor 13 temperature sensor 14 crank position sensor 15 accelerator opening sensor 16 air flow meter 17 vehicle speed sensor 41 tank 42 addition valve 43 reductant passage 44 pump 45 pressure sensor 46 pump rotational speed sensor 47 return passage 48 check valve 100 vehicle

Claims (1)

A catalyst provided in an exhaust passage of an internal combustion engine mounted on a vehicle and purifying exhaust gas using a reducing agent;
An addition valve for supplying a reducing agent to the catalyst;
A pump that discharges the reducing agent,
A reducing agent passage through which the reducing agent flows by connecting the pump and the addition valve;
A pressure detection device for detecting the pressure of the reducing agent in the reducing agent passage;
An abnormality diagnosis device for an exhaust gas purification apparatus for an internal combustion engine, which is a device for performing an abnormality diagnosis for an exhaust gas purification device for an internal combustion engine, comprising:
A determination unit that determines that the condition for performing the abnormality diagnosis is established when the vehicle is stopped;
Based on the pressure drop of the reducing agent detected by the pressure detecting device when the reducing agent is supplied from the addition valve when it is determined by the determination unit that the condition for performing the abnormality diagnosis is satisfied. A diagnostic unit for performing the abnormality diagnosis,
An abnormality diagnosis device for an exhaust gas purification device for an internal combustion engine, comprising:

Images