JP5287506B2 - Sensor abnormality diagnosis device - Google Patents

Description

  The present invention relates to a sensor abnormality diagnosis device.

  When calibrating an oxygen sensor provided on the downstream side of the catalyst after the internal combustion engine is stopped, a technique for filling the atmosphere around the oxygen sensor is known (see, for example, Patent Document 1). However, depending on the temperature of the exhaust pipe and the catalyst, water may be condensed when the exhaust pipe is filled with air. And when this water adheres to a sensor, there exists a possibility that a sensor may break down.

JP 2007-205328 A JP 2008-2272 A JP 2008-64007 A

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a technique capable of suppressing water from adhering to a sensor at the time of sensor abnormality diagnosis in the sensor abnormality diagnosis device. To do.

In order to achieve the above object, the sensor abnormality diagnosis apparatus according to the present invention employs the following means. That is, the sensor abnormality diagnosis device according to the present invention is:
An abnormality diagnosis device for a sensor for diagnosing abnormality of the sensor based on an output value of the sensor when air is introduced into an exhaust passage around a sensor provided in an exhaust passage of an internal combustion engine for detecting a predetermined component in the exhaust gas In
A plurality of air introduction means for introducing air into the exhaust passage around the sensor;
Among the plurality of air introduction means, a selection is made such that the time until the introduction of air into the exhaust passage around the sensor is completed is shorter than the time until water condenses in the exhaust passage. Selection means to
It is characterized by providing.

  The predetermined component may include a plurality of components. Introducing air into the exhaust passage around the sensor means that the gas detected by the sensor is replaced by air from the exhaust. The periphery of the sensor is at least a range detected by the sensor. Here, since the components of air are known in advance, by comparing the output value of the sensor when air is introduced around the sensor with the value (reference value) that should be output by the air component An abnormality of the sensor can be diagnosed. For example, when the difference between the output value of the sensor and the reference value is larger than the threshold value, it can be determined that the sensor is abnormal. This abnormality includes, for example, an abnormality in which the output value of the sensor is offset. Further, the sensor can be calibrated or the output value can be corrected based on the difference between the sensor output value and the reference value.

  A plurality of air introducing means are provided, and the selecting means selects at least one of them and introduces air. Here, the selection means compares the time until the introduction of the air into the exhaust passage around the sensor is completed and the time until the water is condensed in the exhaust passage for each air introduction means. .

  Then, by selecting an air introduction means in which the time until the introduction of air into the exhaust passage around the sensor is completed is shorter than the time until water condenses in the exhaust passage, The sensor abnormality diagnosis can be completed before liquid water is generated. Thereby, it is suppressed that water adheres to the sensor at the time of abnormality diagnosis of the sensor.

In the present invention, the plurality of air introduction means include
Means for causing a gas in the exhaust passage to flow backward from an injection valve provided in the exhaust passage upstream of the sensor and injecting a reducing agent into the exhaust passage;
Means for discharging secondary air into the exhaust passage upstream of the sensor;
Means for opening a throttle provided in an intake passage of the internal combustion engine and opening an EGR valve provided in an EGR passage connecting the exhaust passage and the intake passage;
Means for opening the throttle and motoring the internal combustion engine;
There may be at least two of the above.

  According to the means provided in the exhaust passage upstream of the sensor to reversely flow the gas in the exhaust passage from the injection valve that injects the reducing agent into the exhaust passage, the burned gas in the exhaust passage is sucked into the injection valve. Is done. Then, since the pressure in the exhaust passage decreases, air flows backward from the outlet of the exhaust passage toward the sensor. Thereby, air can be introduced into the exhaust passage around the sensor.

  According to the means for discharging the secondary air into the exhaust passage upstream of the sensor, the secondary air flows toward the sensor. Thereby, air can be introduced into the exhaust passage around the sensor.

  According to the means for opening the throttle provided in the intake passage of the internal combustion engine and opening the EGR valve provided in the EGR passage connecting the exhaust passage and the intake passage, air flows from the intake passage to the exhaust passage through the EGR passage. Thereby, air can be introduced into the exhaust passage around the sensor.

  According to the means for opening the throttle and motoring the internal combustion engine, the air passing through the cylinder from the intake passage is discharged to the exhaust passage. Thereby, air can be introduced into the exhaust passage around the sensor.

  A combination of these means can also introduce air around the sensor.

  In the present invention, a priority is set for each of the air introduction means, and the selection means determines the time until the introduction of air into the exhaust passage around the sensor is completed in the exhaust passage. Among the air introduction means that are shorter than the time until the water condenses, the one having the highest priority can be selected.

  That is, when there are a plurality of air introduction means that complete the introduction of air into the exhaust passage around the sensor before the water is condensed, the one with the highest priority is selected from among the air introduction means. The priority may be determined in advance or may be changed depending on the situation at that time. By doing in this way, selection of an air introduction means becomes easy and selection according to the situation at that time is attained.

  ADVANTAGE OF THE INVENTION According to this invention, in the abnormality diagnosis apparatus of a sensor, it can suppress that water adheres to a sensor at the time of abnormality diagnosis of a sensor.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, its intake system, and an exhaust system. 3 is a time chart showing the relationship between the elapsed time since the internal combustion engine stopped and the NOx concentration around the NOx sensor. It is the flowchart which showed the flow of abnormality diagnosis of the NOx sensor which concerns on an Example.

  Hereinafter, specific embodiments of the sensor abnormality diagnosis apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders. In this embodiment, a urea SCR system is employed.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. The intake passage 2 is provided with a throttle 4 that adjusts the amount of intake air flowing through the intake passage 2.

  A selective reduction type NOx catalyst 5 (hereinafter referred to as NOx catalyst 5) is provided in the middle of the exhaust passage 3.

An injection valve 60 for injecting urea water as a reducing agent into the exhaust gas is attached to the exhaust passage 3 upstream of the NOx catalyst 5. The injection valve 60 is opened by a signal from the ECU 10 described later and injects urea water into the exhaust gas. One end of a urea passage 61 through which urea or gas in the exhaust passage 3 flows is connected to the injection valve 60. The other end of the urea passage 61 branches into two and is connected to a urea water pump 62 that discharges urea water and a suction pump 63 that sucks gas.

When the injection valve 60 is opened while the urea water pump 62 is operated, urea water is injected from the injection valve 60 into the exhaust gas. This urea water is hydrolyzed by the heat of the exhaust gas to become ammonia (NH ₃ ) and is adsorbed on the NOx catalyst 5. This NH ₃ reduces NOx. On the other hand, when the injection valve 60 is opened while operating the suction pump 63, the exhaust in the exhaust passage 3 is sucked into the injection valve 60.

  Further, the internal combustion engine 1 is provided with an EGR device that recirculates a part of the exhaust gas (hereinafter referred to as EGR gas) flowing through the exhaust passage 3 to the intake passage 2. The EGR device includes an EGR passage 70 and an EGR valve 71. The EGR passage 70 connects the exhaust passage 3 upstream of the injection valve 60 and the intake passage 2 downstream of the throttle 4. Through this EGR passage 70, the EGR gas is recirculated. The EGR valve 71 adjusts the amount of EGR gas flowing through the EGR passage 70 by adjusting the passage cross-sectional area of the EGR passage 70.

  Furthermore, one end of an air supply passage 80 through which secondary air flows is connected to the exhaust passage 3 upstream of the injection valve 60. The other end of the air supply passage 80 is connected to the pump 81. When the pump 81 is activated, air is discharged. This air flows through the air supply passage 80 and is supplied into the exhaust passage 3.

A NOx sensor 9 for measuring the concentration of NOx in the exhaust is attached to the exhaust passage 3 downstream of the NOx catalyst 5. The internal combustion engine 1 is provided with a starter motor 11 that rotates the crankshaft of the internal combustion engine 1.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 12 by the driver to detect the engine load, and a crank position sensor for detecting the engine speed. 14 are connected via electric wiring, and the output signals of these various sensors are input to the ECU 10.

  On the other hand, the throttle 10, the starter motor 11, the injection valve 60, the urea water pump 62, the suction pump 63, the EGR valve 71, and the pump 81 are connected to the ECU 10 through electric wiring, and these devices are connected by the ECU 10. Be controlled.

Based on the offset amount (deviation amount from the reference value) of the NOx sensor 9, the ECU 10
An abnormality of the Ox sensor 9 is diagnosed. Further, based on the offset amount of the NOx sensor 9, the NOx
The sensor 9 can also be calibrated. The diagnosis of the abnormality of the NOx sensor 9 and the calibration of the NOx sensor 9 are performed based on the output value when the atmosphere is introduced around the NOx sensor 9. Here, since the atmospheric component is known in advance, the output value of the NOx sensor 9 when the atmospheric air is introduced should be a predetermined value (reference value). For example, since NOx is scarcely contained in the atmosphere, the NOx concentration should be zero when the NOx concentration in the atmosphere is detected by the NOx sensor 9. If the NOx concentration does not become 0, the output value deviates from the reference value by the amount of NOx output from the NOx sensor 9.

Here, when diagnosing the abnormality of the NOx sensor 9, the NOx concentration around the NOx sensor 9 needs to be sufficiently low. That is, if the exhaust gas remains in the exhaust passage 3, it is difficult to diagnose the abnormality of the NOx sensor 9.

FIG. 2 is a time chart showing the relationship between the elapsed time since the internal combustion engine 1 stopped and the NOx concentration around the NOx sensor 9. This is a diagram in the case where no means for introducing air around the NOx sensor 9 is used after the internal combustion engine 1 is stopped. Thus, it takes a certain amount of time for the NOx concentration to sufficiently decrease after the internal combustion engine 1 is stopped. Then, water may condense in the exhaust passage 3 before the NOx concentration is sufficiently lowered. For example, since the NOx sensor 9 measures the NOx concentration while being heated by the heater, the heater becomes high temperature when diagnosing the abnormality of the NOx sensor 9. If condensed water adheres to this high-temperature NOx sensor 9, the NOx sensor 9 may break down.

On the other hand, in this embodiment, when diagnosing the abnormality of the NOx sensor 9, first, the exhaust passage 3
Air is introduced into the interior. This air may be introduced around the NOx sensor 9. That means
It is not necessary to completely fill the exhaust passage 3 with air. In this way, after the NOx concentration around the NOx sensor 9 is lowered, the abnormality of the NOx sensor 9 is diagnosed. That is, the abnormality diagnosis of the NOx sensor 9 is completed before condensed water is generated.

Here, in this embodiment, in order to introduce air around the NOx sensor 9, one of the following (1) to (4) is executed.
(1) Open the injection valve 60 while operating the suction pump 63. Thereby, exhaust flows backward through the injection valve 60. That is, the exhaust valve 3 sucks the exhaust gas in the exhaust passage 3. Then, air is introduced into the exhaust passage 3 from the outlet of the exhaust passage 3.
(2) The pump 81 is operated. Then, air (secondary air) is supplied from the air supply passage 80 into the exhaust passage 3.
(3) Open the throttle 4 and the EGR valve 71. Thereby, the flow of air from the intake passage 2 to the exhaust passage 3 is ensured.
(4) The starter motor 11 is operated while the throttle 4 is opened and the EGR valve 71 is closed. That is, the internal combustion engine 1 is motored by the starter motor 11. As a result, the air that has passed through the cylinder from the intake passage 2 is supplied into the exhaust passage 3.

Thus, in this embodiment, a plurality of means for introducing air around the NOx sensor 9 are provided. The ECU 10 selects one or more means from (1) to (4) and selects the NOx sensor 9
Introduce air around. In addition, other means other than (1) to (4) may be added, and one or more means may be selected from them. These are executed after the fuel injection is stopped when the internal combustion engine 1 is stopped or after the internal combustion engine 1 is stopped.

Hereinafter, a case where the ECU 10 selects one means from the above (1) to (4) will be described. The ECU 10 selects a means capable of introducing air around the NOx sensor 9 before water is condensed in the exhaust passage 3. That is, the time T1 until the water is condensed in the exhaust passage 3 and the time T2 until the introduction of air around the NOx sensor 9 is completed are compared for each means. Then, a means that satisfies T1> T2 is selected.

The time T1 until the water is condensed in the exhaust passage 3 is calculated based on the temperature of the NOx catalyst 5, the outside air temperature, and the like. This time T1 may be obtained by using a well-known calculation formula, or may be obtained in advance through experiments or the like and mapped.

Further, the time T2 until the introduction of air around the NOx sensor 9 is completed is obtained in advance by experiments or the like and stored in the ECU 10.

When there are a plurality of means satisfying T1> T2, for example, a means having the shortest value of T2 may be selected, or a means having the highest priority may be selected. Since the time required for diagnosing the abnormality of the NOx sensor 9 can be shortened by selecting the means having the shortest value of T2, the diagnosis can be completed even if the internal combustion engine 1 is stopped for a short time. . As a result, NOx
The abnormality diagnosis of the sensor 9 can be performed more reliably.

  Further, by selecting the means with the highest priority, selection according to the situation at that time becomes possible. For example, when the amount of power stored in the battery is small, if the starter motor 11 is rotated, it may be difficult to start the internal combustion engine 1 next time. Therefore, the priority of the above (4) is lowered. At this time, the priority is increased in ascending order of power consumption. For example, the priority of (3) is made highest. By increasing the priority in ascending order of power consumption, deterioration of fuel consumption can be suppressed.

  Further, for example, when it is not desired to lower the temperature of the internal combustion engine 1, the priority of (4) in which air passes through the cylinder is lowered. Further, when the hybrid vehicle is running with a motor or when the internal combustion engine 1 is automatically stopped while the vehicle is stopped, the internal combustion engine 1 is likely to start immediately. Increase the priority of the means that can be introduced. This priority varies depending on the performance of the starter motor 11, the suction pump 63, the pump 81, and the like.

  Further, for example, the priority of a predetermined means such as (1) may be made highest in advance.

FIG. 3 is a flowchart showing a flow of abnormality diagnosis of the NOx sensor 9 according to this embodiment. This routine is repeatedly executed by the ECU 10 every predetermined time.

In step S101, it is determined whether the internal combustion engine 1 has been stopped. It may be determined whether or not there is a request to stop the internal combustion engine 1. That is, it is determined whether a condition necessary for diagnosing the abnormality of the NOx sensor 9 is satisfied. If an affirmative determination is made in step S101, the process proceeds to step S102, and if a negative determination is made, the NOx sensor 9
This routine is terminated because the abnormal diagnosis cannot be performed.

  In step S102, 0 is substituted into a counter TC for counting the elapsed time since the internal combustion engine 1 is stopped. That is, 0 is substituted as an initial value. Thereafter, the elapsed time is substituted into the counter TC, for example, every second.

In step S103, a time T1 until water is condensed in the exhaust passage 3 is calculated. It is good also as time until water condenses around the NOx sensor 9. Here, the time T1 is obtained by substituting the temperature of the NOx catalyst 5, the outside air temperature, and the like into previously stored calculation formulas. Alternatively, the relationship between the temperature of the NOx catalyst 5 and the outside air temperature and the time T1 may be mapped, and the time T1 may be obtained from the map. Furthermore, for example, it may be a time until a predetermined temperature (for example, 100 ° C.) or less.

In step S104, time T2 until the introduction of air around the NOx sensor 9 is completed.
Is calculated for each means. For example, the calculation is performed based on a map stored in advance in the ECU 10.

In step S105, a means for introducing air into the vicinity of the NOx sensor 9 is selected.
That is, a means that satisfies T1> T2 is selected. When there are a plurality of units, for example, the unit having the highest priority is selected. In this embodiment, the ECU 10 that processes step S105 corresponds to the selection means in the present invention.

In step S106, the NOx sensor 9 is selected by the means selected in step S105.
Introduce air in the vicinity of

In step S107, the elapsed time TC from the stop of the internal combustion engine 1 is determined by the NOx sensor 9.
It is determined whether or not it is time T2 or more until the introduction of air to the periphery is completed. That is, it is determined whether or not the introduction of air around the NOx sensor 9 is completed. If an affirmative determination is made in step S107, the process proceeds to step S108, and if a negative determination is made, step S107 is executed again. That is, the process does not proceed to the next step until air is introduced in the vicinity of the NOx sensor 9.

In step S108, the NOx concentration error ΔNOx detected by the NOx sensor 9 is calculated. This error ΔNOx is the absolute value of the NOx concentration obtained by the NOx sensor 9.
That is, since the periphery of the NOx sensor 9 is filled with air, the NOx concentration should be 0. At this time, the NOx concentration obtained by the NOx sensor 9 becomes an error as it is.

In step S109, it is determined whether or not the error ΔNOx calculated in step S109 is smaller than a threshold value. This threshold is a lower limit value of an error determined that the NOx sensor 9 is abnormal. If an affirmative determination is made in step S109, the process proceeds to step S110, and if a negative determination is made, the process proceeds to step S111.

In step S110, it is determined that the NOx sensor 9 is normal. Step S
In 111, it is determined that the NOx sensor 9 is abnormal.

In this way, by selecting one of the plurality of air introduction means and introducing air in the vicinity of the NOx sensor 9, it is possible to suppress the condensed water from adhering to the NOx sensor 9. Thereby, the abnormality diagnosis of the NOx sensor 9 can be performed while suppressing the failure of the NOx sensor 9. Further, the output value of the sensor 9 can be corrected based on the error ΔNOx. In this embodiment, the NOx sensor 9 has been described. However, the present invention can be similarly applied to an air-fuel ratio sensor, an oxygen concentration sensor, an HC concentration sensor, and the like.

Reference Signs List 1 internal combustion engine 2 intake passage 3 exhaust passage 4 throttle 5 selective reduction type NOx catalyst 9 NOx sensor 11 starter motor 12 accelerator pedal 13 accelerator opening sensor 14 crank position sensor 60 injection valve 61 urea passage 62 urea water pump 63 suction pump 70 EGR Passage 71 EGR valve 80 Air supply passage 81 Pump

Claims (3)

An abnormality diagnosis device for a sensor for diagnosing abnormality of the sensor based on an output value of the sensor when air is introduced into an exhaust passage around a sensor provided in an exhaust passage of an internal combustion engine for detecting a predetermined component in the exhaust gas In
A plurality of air introduction means for introducing air into the exhaust passage around the sensor;
Among the plurality of air introduction means, a selection is made such that the time until the introduction of air into the exhaust passage around the sensor is completed is shorter than the time until water condenses in the exhaust passage. Selection means to
An abnormality diagnosis apparatus for a sensor, comprising: The plurality of air introduction means include
Means for causing a gas in the exhaust passage to flow backward from an injection valve provided in the exhaust passage upstream of the sensor and injecting a reducing agent into the exhaust passage;
Means for discharging secondary air into the exhaust passage upstream of the sensor;
Means for opening a throttle provided in an intake passage of the internal combustion engine and opening an EGR valve provided in an EGR passage connecting the exhaust passage and the intake passage;
Means for opening the throttle and motoring the internal combustion engine;
The sensor abnormality diagnosis device according to claim 1, wherein the sensor abnormality diagnosis device is at least two of the two.   A priority is set for each of the air introduction means, and the selection means waits until the introduction of air into the exhaust passage around the sensor is completed until water is condensed in the exhaust passage. 3. The sensor abnormality diagnosis device according to claim 1, wherein the air introduction means having the highest priority is selected from the air introduction means shorter than the time.

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