JP4055476B2 - Abnormality detection device for catalyst downstream oxygen sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst downstream oxygen sensor abnormality detection device that detects deterioration of a downstream oxygen sensor provided downstream of a catalytic converter of an engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a technique for performing abnormality detection on a downstream oxygen sensor provided downstream of a catalytic converter is known. When detecting an abnormality of the downstream oxygen sensor based on the responsiveness of the downstream catalyst sensor after the combustion air-fuel ratio changes, it is difficult to detect the abnormality with high accuracy due to the influence of the catalytic converter provided upstream thereof. It is.
[0003]
In general, the newer the catalytic converter, the higher the oxygen adsorption capacity, so that even if the upstream air-fuel ratio of the catalytic converter changes, it takes time for the change to appear downstream. On the other hand, when the catalytic converter deteriorates, the oxygen adsorption capacity decreases, so that the change appears downstream of the catalytic converter immediately after the upstream air-fuel ratio of the catalytic converter changes.
[0004]
In other words, when trying to detect an abnormality in the response of the sensor output of the downstream oxygen sensor after the combustion air-fuel ratio has changed, the response of the catalytic converter is deteriorated despite the deterioration of the response of the downstream oxygen sensor. There is a possibility that it may be erroneously determined that the responsiveness of the downstream oxygen sensor is normal due to the deterioration.
[0005]
Thus, when detecting an abnormality of the downstream oxygen sensor, the influence of the catalytic converter is large, and it is difficult to detect the abnormality with high accuracy. As a technique for solving this, a technique disclosed in JP-A-9-170966 is known. According to this technique, in order to eliminate the influence of the catalytic converter and accurately detect the abnormality of the downstream oxygen sensor, the determination value is provided on each of the rich side and the lean side. Then, the time required to change from the predetermined voltage to the other predetermined voltage is measured as a response time with respect to the predetermined voltage corresponding to the determination value of the rich side and the lean side, and if this response time is long, the downstream oxygen This is a technology that indicates a sensor abnormality.
[0006]
[Problems to be solved by the invention]
However, in the technique disclosed in the above-described conventional publication, the abnormality detection of the downstream oxygen sensor is not executed unless the determination values for the lean side and the rich side are exceeded. For this reason, for example, when the sensor output gradually moves from the lean determination value toward the rich side due to excessive deterioration of the responsiveness of the downstream oxygen sensor, there is a possibility that the sensor abnormality cannot be detected. Further, even if it can be detected, the time until detection becomes long.
[0007]
Accordingly, an object of the present invention is to provide a downstream oxygen sensor abnormality detection device capable of reliably detecting abnormality of the downstream oxygen sensor.
[0008]
[Means for Solving the Problems]
Therefore, by measuring the time from the determination that the exhaust gas air-fuel ratio in the exhaust passage is switched by the air-fuel ratio changeover judging part as in the invention of claim 1, and the output of the downstream oxygen sensor, said first The time from when the predetermined value is equal to or less than the second predetermined value leaner than the predetermined value is counted, and the minimum value of the output value of the downstream oxygen sensor is calculated, and the output of the downstream oxygen sensor is the second predetermined value. The time from when it is determined that the minimum value of the downstream sensor does not become the first determination value or less and the exhaust gas air-fuel ratio has been switched until the count value after the value becomes equal to or less than the predetermined count value. An abnormality detection unit is provided that determines that the downstream oxygen sensor is abnormal when it is determined that the time is longer than the predetermined time .
[0009]
Thereby, the minimum value of the downstream sensor does not become the first determination value or less until the count value after the output of the downstream oxygen sensor becomes the second predetermined value or less becomes the predetermined count value, and Since it is determined that the downstream oxygen sensor is abnormal when it is determined that the time from when it is determined that the exhaust gas air-fuel ratio has been switched is longer than the predetermined time, it is ensured when the air-fuel ratio in the exhaust passage is switched. Anomaly detection can be performed.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a vehicle engine will be described with reference to the drawings.
[0022]
FIG. 1 is a schematic configuration diagram of an embodiment of the present invention. An air flow meter 3 is provided in the intake passage 2 of the engine 1. The air flow meter 3 directly measures the intake air amount Q guided through the air cleaner 4. Further, the intake passage 2 is provided with a throttle valve 6 that opens and closes according to the amount of operation of the accelerator 5 by the driver and adjusts the intake amount Q supplied to the engine 1. Reference numeral 21 denotes a throttle opening sensor that detects the opening of the throttle valve 6, and reference numeral 22 denotes an idle switch that outputs an ON signal when the throttle valve 6 is fully closed. Each cylinder of the engine 1 is provided with a fuel injection valve 8 for supplying pressurized fuel to the intake port from the fuel supply system 7 to each cylinder.
[0023]
Further, the distributor 9 is provided with a reference position sensor 10 that generates a reference position detection signal every 720 crank angles (° C. A) and a crank angle sensor 11 that generates a crank angle detection signal every 30 ° C. A. Yes.
[0024]
Furthermore, the water jacket 12 of the cylinder block of the engine 1 is provided with a water temperature sensor 13 for detecting the cooling water temperature Thw. On the other hand, the exhaust system is provided with a three-way catalyst 15 for simultaneously purifying harmful components (HC, CO, NOx) in the exhaust gas downstream of the exhaust manifold 14. A linear A / F sensor (A / F sensor) 16 is provided on the upstream side of the three-way catalyst 15, that is, the exhaust manifold 14, and a downstream O 2 sensor is provided on the exhaust pipe 17 on the downstream side of the three-way catalyst 15. 18 is provided. As is well known, these upstream A / F sensors 16 are sensors that linearly detect the air-fuel ratio of exhaust gas in the exhaust manifold 14, and the downstream O2 sensor 18 is that the air-fuel ratio is lean relative to the stoichiometric air-fuel ratio. Different output voltages are generated depending on whether they are rich.
[0025]
Reference numeral 19 denotes an alarm for issuing a warning to the driver when it is determined by the electronic control unit (ECU) 20 described later that the downstream O2 sensor 18 has deteriorated. The ECU 20 is configured as a microcomputer, for example, and is provided with an A / D converter 101, an I / O port 102, a CPU 103, a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like as is well known.
[0026]
Next, air-fuel ratio feedback control performed by the ECU 20 will be described. The ECU 20 described above performs feedback control based on the output value of the linear A / F sensor 16 in order to control the air-fuel ratio in consideration of the purification characteristics of the three-way catalyst 15. That is, the ECU 20 calculates the feedback correction coefficient based on the deviation between the target air-fuel ratio and the actual air-fuel ratio so that the output value of the air-fuel ratio detected by the linear A / F sensor 16 becomes the target air-fuel ratio. Then, the fuel injection amount by the injector 8 is calculated using this feedback correction coefficient.
[0027]
Next, calculation of the fuel injection amount will be described. First, a basic injection time determined by the intake air amount Q and the engine speed NE is set using a preset map. Then, the final fuel injection time is calculated by multiplying the basic injection time by a feedback correction coefficient calculated based on the deviation between the target air-fuel ratio and the actual air-fuel ratio. Thereby, the air-fuel ratio can be controlled so as to follow the target air-fuel ratio.
[0028]
This target air-fuel ratio is corrected by sub feedback control based on the output of the downstream O2 sensor 18. That is, when considering the purification characteristics of the three-way catalyst 15, the air-fuel ratio detected on the downstream side of the three-way catalyst 15 is preferably controlled in the vicinity of the theoretical air-fuel ratio. For this reason, in the present embodiment, the target air-fuel ratio is corrected based on the rich / lean output of the downstream O2 sensor. As described above, the air-fuel ratio control that makes the best use of the purification characteristics of the three-way catalyst 15 is executed by the feedback control by the linear A / F sensor 16 and the sub-feedback control by the downstream O2 sensor 18.
[0029]
By the way, when the downstream O2 sensor 18 becomes abnormal, it may be difficult to execute the accurate air-fuel ratio control as described above. Therefore, the present embodiment is characterized by the abnormality detection of the downstream O2 sensor 18. When abnormality detection is performed for the downstream O2 sensor 18 provided downstream of the three-way catalyst 15, the abnormality of the downstream oxygen sensor is detected based on the response of the downstream catalyst sensor after the combustion air-fuel ratio changes. try to. In this case, it is difficult to accurately detect an abnormality due to the influence of the three-way catalyst 15 provided upstream thereof.
[0030]
That is, the three-way catalyst 15 has an ability to store oxygen, and even if the air-fuel ratio on the upstream side of the three-way catalyst 15 changes, there is a response delay until the change in the air-fuel ratio appears on the downstream side. The oxygen storage capacity of the three-way catalyst 15 decreases with the change with time of the three-way catalyst 15. As a result, the response delay is reduced from when the air-fuel ratio on the upstream side of the three-way catalyst 15 changes until when the air-fuel ratio change appears downstream.
[0031]
Accordingly, when an abnormality is to be detected by the response of the sensor output of the downstream O2 sensor after the combustion air-fuel ratio has changed, the three-way catalyst is deteriorated despite the deterioration of the response of the downstream oxygen sensor. There is a possibility that it is erroneously determined that the response of the downstream O2 sensor is normal due to the deterioration of 15.
[0032]
In the present invention, in view of such circumstances, abnormality of the downstream O2 sensor 18 is executed with high accuracy by the following program. First, the main program of this embodiment will be described with reference to FIG. This program is a program that is started when the output value of the downstream O2 sensor 18 is equal to or greater than the first predetermined value on the rich side and the fuel cut is being executed in the engine 1. And after starting, it is a program executed for every predetermined period.
[0033]
First, in step S101, the F / C timer is incremented to measure the time after the output of the downstream O2 sensor is richer than the first predetermined value on the rich side and the fuel cut is executed. Proceed to S102. In step S102, it is determined whether or not the downstream O2 sensor 18 is leaner than the second predetermined value. The second predetermined value is a value on the rich side, and is set as a value on the lean side with respect to the first predetermined value.
[0034]
In the present embodiment, the response of the downstream O2 sensor 18 is detected when the fuel is cut. The method detects an abnormality only when the output of the downstream O2 sensor 18 becomes leaner than the first predetermined value set on the rich side to the second predetermined value set on the lean side. Execute. That is, the time until the output exceeds the second predetermined value may vary depending on the degree of deterioration of the downstream O2 sensor 18 and the mounting position of the downstream O2 sensor 18. Therefore, the second predetermined value is a predetermined value set to absorb this variation.
[0035]
When the output of the downstream O2 sensor 18 is on the rich side (larger) than the second predetermined value, a negative determination is made in step S102 (NO), and this routine is ended as it is. On the other hand, if the output is leaner (smaller) than the second predetermined value, an affirmative determination (YES) is made in step S102, and the process proceeds to step S103. In step S103, the counter that is counted after the output of the downstream O2 sensor 18 becomes leaner than the second predetermined value is incremented. At the same time, the minimum value VOX2min of the output value of the downstream O2 sensor 18 is calculated.
[0036]
In the calculation of the minimum value VOX2min, the past minimum value VOX2min and the current output of the downstream O2 sensor 18 are compared each time after the output of the downstream O2 sensor 18 exceeds the second predetermined value. When the output is smaller, the minimum value VOX2min is updated to the current value. Thus, when the process of step S103 is completed, the process proceeds to step S104, and it is determined whether or not the counter is smaller than a predetermined count value. If this counter is larger than the predetermined count value, a negative determination is made in step S104 (NO), and this routine is terminated as it is.
[0037]
On the other hand, when the counter is smaller than the predetermined count value, an affirmative determination (YES) is made in step S104, and the process proceeds to step S105. After step S105, the abnormality determination is executed based on the minimum value VOX2min of the downstream O2 sensor 18.
[0038]
First, in step S105, it is determined whether or not the minimum value VOX2min of the downstream O2 sensor 18 calculated in step S103 is leaner than the first determination value. If the minimum value VOX2min is leaner (smaller) than the first determination value, a negative determination (NO) is made in step S105, the process proceeds to step S106, normal determination is made, and this routine is terminated. On the other hand, if the minimum value VOX2min is richer (larger) than the first determination value, an affirmative determination (YES) is made in step S105, and the process proceeds to step S107.
[0039]
In step S107, it is determined whether or not the fuel cut time elapsed by the F / C timer measured in step S101 exceeds a predetermined time. If the fuel cut time does not exceed the predetermined time, a negative determination (NO) is made in step S107, and this routine is ended as it is. On the other hand, if the fuel cut time exceeds the predetermined time, an affirmative determination (YES) is made in step S107 and the process proceeds to step S108. In step S108, it is determined that the downstream O2 sensor 18 is abnormal, and this routine is terminated by turning on the alarm 19 or the like.
[0040]
As described above, in the present embodiment, the minimum value VOX2min of the downstream O2 sensor 18 is greater than the first determination value at a predetermined time after the output of the downstream O2 sensor 18 becomes leaner than the second predetermined value. In the case of the rich side, it was determined that the downstream O2 sensor 18 is abnormal. As described above, in the present embodiment, the abnormality detection of the downstream O2 sensor 18 is performed for a predetermined time, so that the abnormality detection can be surely executed without exceeding the first determination value set on the lean side.
[0041]
Below, the operation example is demonstrated using the time chart shown in FIG. 3 about the above-mentioned program. In FIG. 3A, a fuel cut flag is shown. This flag is turned on when a fuel cut condition is satisfied during operation of the engine 1. When the fuel cut flag is turned on at time T0, it is determined whether the output of the downstream O2 sensor 18 shown in FIG. 3B is richer than the first predetermined value. At this time, when the fuel cut flag is on and the output value VOX2 is equal to or higher than the first predetermined value, the program shown in FIG. 2 is started and thereafter repeatedly executed at predetermined time intervals.
[0042]
When the output VOX2 exceeds the second predetermined value at time T1, counting for a predetermined period set in advance is started. At this time, update processing of the minimum value VOX2min of the downstream O2 sensor 18 is performed. Then, when the preset predetermined period elapses and time T2 is reached, the minimum value VOX2min calculated so far (in FIG. 3, the output value VOX2 at time T2) and the first preset value are set. Compare judgment values. Based on the comparison result, abnormality determination of the downstream O2 sensor 18 is executed.
[0043]
That is, in the present embodiment, the abnormality detection of the downstream O2 sensor 18 is performed based on the change amount of the output VOX2 in a predetermined period, so that the abnormality determination is surely executed when the abnormality detection program is executed. be able to.
[0044]
In the present embodiment, the air-fuel ratio switching determination means corresponds to step S102 in the flowchart of FIG. 2, and the abnormality detection means corresponds to the flowchart of FIG.
[0045]
(Other Example 1)
In the present embodiment, the engine 1 that performs feedback control and sub-feedback control is described. However, the present invention is not limited to this, and any engine that has an O2 sensor downstream of the three-way catalyst 15 may be used. Similarly, the three-way catalyst 15 is not limited to this as long as it has an oxygen storage capacity.
[0046]
(Other Example 2)
In the present embodiment, it is described that the fuel cut is being executed. However, the present invention is not limited to this, and for the purpose of improving the detection frequency, for example, the target air-fuel ratio is switched stepwise from the rich side to the lean side. Anomaly detection may be performed when The configuration for determining this switching corresponds to the air-fuel ratio switching determination means described in the claims.
[0047]
In the present embodiment, the first predetermined value is set on the rich side, and the program shown in FIG. 2 is executed at the time of output exceeding the first predetermined value. On the other hand, in this embodiment, a third predetermined value is set on the lean side, and when the air-fuel ratio is stepwise switched to the rich side when the output is leaner than the third predetermined value, the rear side is set. The response abnormality of the O2 sensor 18 is executed.
[0048]
Specifically, the fuel cut time after the output VOX2 of the rear O2 sensor 18 becomes richer than the fourth predetermined value is counted. The fourth predetermined value is a richer value than the third predetermined value. At this time, the maximum output value VOX2max of the rear O2 sensor 18 is updated. Then, it is determined that the rear O2 sensor 18 is abnormal when the value of the output VOX2max is leaner than the second determination value when the predetermined fuel cut time has elapsed.
[0049]
As described above, in this embodiment, even when the air-fuel ratio is switched stepwise from the lean side to the rich side, the abnormality detection of the rear O2 sensor 18 can be executed as in the embodiment.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.
FIG. 2 is a flowchart for detecting an abnormality of the rear O2 sensor in the embodiment.
FIG. 3 is a time chart when the embodiment is applied.
[Brief description of symbols]
1 ... Engine,
2 ... Intake passage,
6 ... Throttle valve,
7 ... Fuel supply system,
8 ... Fuel injection valve,
15 ... Three-way catalyst,
16: Linear A / F sensor,
17 ... exhaust pipe,
18: Downstream O2 sensor.

Claims (1)

A catalytic converter disposed in the engine exhaust system to purify harmful gas components contained in the exhaust gas in the exhaust passage;
A downstream oxygen sensor disposed downstream of the catalytic converter to detect an exhaust gas air-fuel ratio in the exhaust passage;
Air-fuel ratio switching determination means for determining whether or not a fuel cut has been executed when the output value of the downstream oxygen sensor is equal to or greater than the first predetermined value on the rich side ;
The time after the air-fuel ratio switching determining means determines that the exhaust gas air-fuel ratio in the exhaust passage has been switched is measured, and the output of the downstream oxygen sensor is leaner than the first predetermined value. Counting the time after the second predetermined value or less is counted, calculating the minimum value of the downstream oxygen sensor output value, and counting after the downstream oxygen sensor output is less than or equal to the second predetermined value It has been determined that the minimum value of the downstream sensor is not less than or equal to the first determination value before the value reaches the predetermined count value, and that the time from when it is determined that the exhaust gas air-fuel ratio has been switched is longer than the predetermined time An abnormality detection device for a catalyst downstream oxygen sensor , comprising: an abnormality detection means for determining that the downstream oxygen sensor is abnormal sometimes.

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