JP2021127702A - Abnormality diagnostic device for gas sensor - Google Patents

Abstract

To provide an abnormality diagnostic device for a gas sensor, which executes abnormality diagnosis of the gas sensor with less reduced accuracy.SOLUTION: An abnormality diagnostic device diagnoses abnormality of a gas sensor according to an output value of the gas sensor provided in an exhaust passage while increasing/decreasing a fuel injection amount of a fuel injection valve at a predetermined period to increase/decrease an air-fuel ratio of an exhaust gas flowing in the exhaust passage of an engine. In this case, when a reflow of the exhaust gas is performed by an EGR device, the abnormality diagnosis of the gas sensor is executed at a period set longer than when the reflow of the exhaust gas is not performed by the EGR device.SELECTED DRAWING: Figure 2

Description

The present invention relates to an abnormality diagnostic device for a gas sensor.

It is known that an abnormality of the gas sensor can be diagnosed according to the output value of the gas sensor when the air-fuel ratio of the exhaust gas is increased or decreased (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-030358

If a part of the exhaust gas is returned to the intake passage by the EGR device, the air-fuel ratio of the exhaust gas may deviate from the desired air-fuel ratio. This may reduce the accuracy of the gas sensor abnormality diagnosis.

Therefore, an object of the present invention is to provide a gas sensor abnormality diagnosis device in which a decrease in accuracy of gas sensor abnormality diagnosis is suppressed.

The above purpose is to increase or decrease the fuel injection amount of the fuel injection valve at a predetermined cycle so that the air-fuel ratio of the exhaust gas flowing through the exhaust passage of the engine increases or decreases, and according to the output value of the gas sensor provided in the exhaust passage. An EGR device for diagnosing an abnormality of the gas sensor, which recirculates a part of the exhaust gas flowing through the exhaust passage to the intake passage of the engine, is provided, and the exhaust gas recirculates by the EGR device. When the abnormality diagnosis of the gas sensor is executed when the above is executed, the abnormality diagnosis device of the gas sensor is set to have a longer cycle as compared with the case where the exhaust gas is not recirculated by the EGR device. Can be achieved by.

According to the present invention, it is possible to provide a gas sensor abnormality diagnosis device in which a decrease in accuracy of gas sensor abnormality diagnosis is suppressed.

FIG. 1 is a schematic configuration diagram of an engine system of this embodiment. FIG. 2A is a graph showing the fuel injection amount and the air-fuel ratio of the exhaust gas at the time of executing the abnormality diagnosis of the air-fuel ratio sensor, and FIG. 2B shows the fuel when the switching cycle of the increase / decrease of the fuel injection amount is expanded. It is a graph which showed the injection amount and the air-fuel ratio of exhaust gas. FIG. 3 is a graph showing the relationship between the length of the switching cycle and the rate of change of the output voltage per unit time of the air-fuel ratio sensor when the EGR rate is 21% and the exhaust gas is recirculated. FIG. 4 is a flowchart showing an example of control executed by the ECU. FIG. 5A is a map defining the relationship between the intake air amount and the target switching time, FIG. 5B is a map defining the relationship between the EGR rate and the correction coefficient, and FIG. 5C is the intake air amount and the EGR rate. This is a three-dimensional map that defines the relationship between the target switching time and the target switching time.

FIG. 1 is a schematic configuration diagram of an engine system of this embodiment. The engine 20 is an example of an internal combustion engine, and burns the air-fuel mixture in the combustion chamber 23 in the cylinder head 22 installed on the cylinder block 21 in which the piston 24 is housed to reciprocate the piston 24. The reciprocating motion of the piston 24 is converted into the rotational motion of the crankshaft 26. An oil pan 21a for storing lubricating oil is provided in the lower part of the cylinder block 21. Although not shown, the engine 20 is an in-line 4-cylinder engine having four cylinders, but the engine 20 is not limited thereto.

The cylinder head 22 of the engine 20 is provided with an intake valve 42 for opening and closing the intake port 10i and an exhaust valve 44 for opening and closing the exhaust port 30e for each cylinder. Further, an ignition plug 27 for igniting the air-fuel mixture in the combustion chamber 23 is attached to the top of the cylinder head 22 for each cylinder.

The intake port 10i of each cylinder is connected to the surge tank 18 via a branch pipe of each cylinder. An intake pipe 10 is connected to the upstream side of the surge tank 18, and an air cleaner 19 is provided at the upstream end of the intake pipe 10. The intake pipe 10 is provided with an air flow meter 15 for detecting the intake air amount and an electronically controlled throttle valve 13 in this order from the upstream side.

Further, a port injection valve 12 for injecting fuel into the intake port 10i is installed in the intake port 10i of each cylinder. The fuel injected from the port injection valve 12 is mixed with the intake air to form an air-fuel mixture, and this air-fuel mixture is sucked into the combustion chamber 23 when the intake valve 42 is opened, compressed by the piston 24, and ignited by the spark plug 27. Be burned. The port injection valve 12 is an example of a fuel injection valve.

The exhaust port 30e of each cylinder is connected to the exhaust pipe 30 via a branch pipe for each cylinder. The exhaust pipe 30 is provided with a three-way catalyst 31. An air-fuel ratio sensor 33 for detecting the air-fuel ratio of the exhaust gas is installed on the upstream side of the three-way catalyst 31.

An EGR pipe 50 that communicates the exhaust pipe 30 and the intake pipe 10 is provided. The EGR pipe 50 is provided with an EGR valve 52 whose opening degree can be adjusted. The EGR tube 50 and the EGR valve 52 correspond to an EGR device. When the EGR valve 52 opens, a part of the exhaust gas is recirculated to the intake pipe 10, and by adjusting the opening degree of the EGR valve 52, the amount of EGR gas relative to the total amount of intake gas sucked into the combustion chamber 23 The EGR rate, which is a ratio, can be adjusted. The EGR rate referred to here is an external EGR rate. The EGR tube 50 may be provided with an EGR cooler.

The ECU (Electronic Control Unit) 60 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). The ECU 60 controls the engine 20 by executing a program stored in RAM or ROM. The ECU 60 is a control device for the engine 20. Further, the ECU 60 executes an abnormality diagnosis of the air-fuel ratio sensor 33 when a predetermined condition is satisfied, which will be described in detail later. The ECU 60 is an example of an abnormality diagnosis device for the air-fuel ratio sensor 33.

The spark plug 27, the throttle valve 13, the port injection valve 12, and the EGR valve 52 described above are electrically connected to the ECU 60. Further, the ECU 60 includes an accelerator opening sensor 11 for detecting the accelerator opening, a throttle opening sensor 14 for detecting the throttle opening of the throttle valve 13, an air flow meter 15 for detecting the intake air amount, an air fuel ratio sensor 33, and a crank shaft. A crank angle sensor 25 that detects the crank angle of 26, a water temperature sensor 29 that detects the temperature of the cooling water of the engine 20, and various other sensors are electrically connected. The ECU 60 controls the spark plug 27, the throttle valve 13, the port injection valve 12, the EGR valve 52, etc. so that a desired output can be obtained based on the detection values of various sensors, and controls the ignition timing, fuel injection amount, and the like. It controls the fuel injection timing, throttle opening, EGR rate, etc.

Next, the abnormality diagnosis of the air-fuel ratio sensor 33 will be described. When a predetermined condition is satisfied, the ECU 60 executes an abnormality diagnosis of the air-fuel ratio sensor 33. In the abnormality diagnosis of the air-fuel ratio sensor 33, the fuel injection amount of the port injection valve 12 is increased or decreased so that the air-fuel ratio of the exhaust gas increases or decreases, specifically, increases or decreases between the desired rich air-fuel ratio and the lean air-fuel ratio. Is controlled. Based on the rate of change of the output voltage of the air-fuel ratio sensor 33 when the fuel injection amount is increased or decreased in this way, it is diagnosed whether the air-fuel ratio sensor 33 is normal or abnormal. The predetermined condition described above is, for example, a case where the engine 20 is in an idle operation state, the air-fuel ratio sensor 33 is in an activated state, and the abnormality diagnosis is not completed after the ignition is turned on. The details of the abnormality diagnosis will be described later.

Next, it will be described that the EGR rate affects the accuracy of the abnormality diagnosis of the air-fuel ratio sensor 33. FIG. 2A is a graph showing the fuel injection amount and the air-fuel ratio of the exhaust gas at the time of executing the abnormality diagnosis of the air-fuel ratio sensor 33. The fuel injection amount from the port injection valve 12 is increased or decreased in the switching cycle T. FIG. 2A shows the transition of the air-fuel ratio of the exhaust gas when the EGR rate is 0% and when it is 21%. Regardless of the EGR rate, if the fuel injection amount is set to a large value, the air-fuel ratio of the exhaust gas also gradually decreases, aiming for the rich side, and the fuel injection amount is set to a small value. If so, the air-fuel ratio of the exhaust gas gradually increases and aims at the lean side. In this way, the air-fuel ratio of the exhaust gas increases or decreases.

In the abnormality diagnosis of the air-fuel ratio sensor 33, the air-fuel ratio of the exhaust gas is controlled to increase or decrease in this way. The increase / decrease in the air-fuel ratio of the exhaust gas is determined by the injection amount of the port injection valve 12 so that the air-fuel ratio of the exhaust gas becomes the desired rich air-fuel ratio (hereinafter referred to as the rich injection amount) and the desired lean air-fuel ratio. It is realized by alternately switching to the injection amount (hereinafter, referred to as lean injection amount). Specifically, when the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 33 reaches the desired rich air-fuel ratio after the injection amount is switched to the rich injection amount, the injection amount is switched to the lean injection amount. After the injection amount is switched to the lean injection amount, the injection amount is switched to the rich injection amount when the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 33 reaches the desired lean air-fuel ratio. The switching cycle is set.

The abnormality diagnosis is performed based on the rate of change of the output voltage of the air-fuel ratio sensor 33 per unit time during the execution of the increase / decrease control of the air-fuel ratio of the exhaust gas. This is because the rate of change in the output voltage of the air-fuel ratio sensor 33 increases as the rate of change in the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 33 increases. Here, the rate of change of the output voltage when the air-fuel ratio sensor 33 is normal corresponds to the slope of the air-fuel ratio of the exhaust gas shown in FIG. 2A. For example, when the absolute value of the rate of change of the air-fuel ratio sensor 33 is equal to or more than a predetermined threshold value, the air-fuel ratio sensor 33 is diagnosed as having good responsiveness, and when it is less than the threshold value, the air-fuel ratio sensor 33 is diagnosed as normal. The air-fuel ratio sensor 33 can be diagnosed as abnormal as the responsiveness of the air-fuel ratio sensor 33 is reduced.

Here, comparing the cases where the EGR rate is 0% and 21% as shown in FIG. 2A, the amplitude of the air-fuel ratio of the exhaust gas is smaller when the EGR rate is 21%. Therefore, the rate of change of the output voltage of the air-fuel ratio sensor 33 differs depending on whether the EGR rate is 0% or 21%. Therefore, even if the air-fuel ratio sensor 33 is diagnosed as normal because the rate of change of the output voltage of the air-fuel ratio sensor 33 is equal to or higher than the threshold value when the EGR rate is 0%, it is empty when the EGR rate is 21%. The air-fuel ratio sensor 33 may be diagnosed as abnormal because the rate of change of the output voltage of the fuel ratio sensor 33 is less than the threshold value. As described above, the accuracy of abnormality diagnosis may decrease depending on the magnitude of the EGR rate.

The reason why the amplitude of the air-fuel ratio becomes smaller when the EGR rate is 21% is considered as follows. As described above, in the abnormality diagnosis, the injection amount of the port injection valve 12 is alternately switched between the rich injection amount and the lean injection amount. When the EGR rate is 21%, when the lean injection amount is switched to the rich injection amount, the lean exhaust gas generated when the lean injection amount is set is sent to the intake pipe 10 via the EGR pipe 50. When the exhaust gas that is circulated and is originally rich due to the rich injection amount and the circulated lean exhaust gas are mixed and the exhaust gas that is leaner than the desired rich air-fuel ratio is supplied to the air-fuel ratio sensor 33. Because it can be considered. Similarly, when the rich injection amount is switched to the lean injection amount, the rich exhaust gas generated when the rich injection amount is set is returned to the intake pipe 10 via the EGR pipe 50, and lean injection is performed. This is because it is considered that the exhaust gas that is originally lean depending on the amount and the exhaust gas that is recirculated rich are mixed, and the exhaust gas that is richer than the desired lean air-fuel ratio is supplied to the air-fuel ratio sensor 33. .. As described above, the exhaust gas is returned from the EGR pipe 50 to the intake pipe 10 so as to cancel the desired air-fuel ratio of the exhaust gas generated by the injection amount of the set port injection valve 12, so that the air-fuel ratio sensor 33 The amplitude of the air-fuel ratio of the exhaust gas to be detected becomes smaller.

FIG. 2B is a graph showing the fuel injection amount and the air-fuel ratio of the exhaust gas when the switching cycle of increasing / decreasing the fuel injection amount is expanded. FIG. 2B shows a case where the EGR rate is 21%. By setting the switching cycle Ta longer than the switching cycle T shown in FIG. 2A, the amplitude of the air-fuel ratio of the exhaust gas is larger than that in the case of the switching cycle T. The reason for this is considered as follows. When the lean injection amount is switched to the rich injection amount, the lean exhaust gas Gl is returned to the intake pipe 10 via the EGR pipe 50 and is originally rich because it is switched to the rich injection amount as described above. The exhaust gas Gm1 in which the exhaust gas Gr and the recirculated lean exhaust gas Gr are mixed is supplied to the air-fuel ratio sensor 33. Next, a part of the mixed exhaust gas Gm1 is returned to the intake pipe 10 via the EGR pipe 50 again, and the exhaust gas Gm2 in which the originally rich exhaust gas Gr and the returned exhaust gas Gm1 are mixed is empty. It is supplied to the fuel ratio sensor 33. Here, the air-fuel ratio of the exhaust gas Gm2 is on the rich side of the air-fuel ratio of the exhaust gas Gm1. By repeating this over a predetermined time, the air-fuel ratio of the rich exhaust gas due to the setting of the rich injection amount and the exhaust gas recirculated to the intake pipe 10 via the EGR pipe 50 Exhaust gas, which is substantially the same as the air-fuel ratio and has a desired rich air-fuel ratio, is supplied to the air-fuel ratio sensor 33. Similarly, when the rich injection amount is switched to the lean injection amount, the air-fuel ratio of the lean exhaust gas due to the lean injection amount being set gradually over time, and the intake pipe 10 via the EGR pipe 50 The air-fuel ratio of the exhaust gas recirculated to the air-fuel ratio is substantially the same as that of the exhaust gas, and the exhaust gas having a desired lean air-fuel ratio is supplied to the air-fuel ratio sensor 33.

As described above, by expanding the switching cycle, the exhaust gas having an air-fuel ratio substantially the same as the air-fuel ratio of the desired exhaust gas generated by the injection amount of the set port injection valve 12 can be transferred from the exhaust pipe 30 to the EGR pipe 50. It is possible to secure a period until the gas is returned to the intake pipe 10 through the air. Therefore, it is possible to secure the amplitude of the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 33. As a result, even when the EGR rate is 21%, the abnormality diagnosis of the air-fuel ratio sensor 33 can be accurately performed.

FIG. 3 is a graph showing the relationship between the length of the switching cycle and the rate of change of the output voltage per unit time of the air-fuel ratio sensor 33 when the EGR rate is 21% and the exhaust gas is recirculated. The horizontal axis shows the length of the switching cycle, and the vertical axis shows the magnitude of the rate of change of the output voltage. As shown in FIG. 3, the absolute value of the rate of change of the output voltage increases as the switching cycle expands. Therefore, in the present embodiment, in the ECU 60, the difference in the rate of change of the output voltage when the air-fuel ratio sensor 33 is normal at the time of abnormality diagnosis is small between the case where the EGR rate is 0% and the case where the EGR rate is 21%. As described above, the switching cycle is set to be longer in the case of 21% than in the case of 0%. The switching cycle is preferably set so that the injection amount can be switched when, for example, the air-fuel ratio of the exhaust gas reaches a desired air-fuel ratio. In other words, it is not preferable to lengthen the switching cycle so that the air-fuel ratio of the exhaust gas is kept constant at a desired air-fuel ratio. Therefore, the switching cycle is appropriately set in consideration of experimental results and the like, which will be described in detail later.

Next, the control executed by the ECU 60 will be described. FIG. 4 is a flowchart showing an example of the control executed by the ECU 60. This control is repeatedly executed. First, the ECU 60 determines whether or not the air-fuel ratio sensor 33 is being diagnosed for abnormality (step S1). If No in step S1, this control ends.

If Yes in step S1, the ECU 60 counts the time s from the switching of the injection amount (step S3). The time from the switching of the injection amount is the time from the switching from the rich injection amount to the lean injection amount or the switching from the lean injection amount to the rich injection amount, which is executed during the abnormality diagnosis. Immediately after the abnormality diagnosis is started, it is the time from switching from the injection amount immediately before the abnormality diagnosis start to the rich injection amount or the lean injection amount at the time of the abnormality diagnosis.

Next, the ECU 60 measures the rate of change of the output voltage value of the air-fuel ratio sensor 33 (step S5). Next, the ECU 60 calculates the target switching time S (step S7). The target switching time S is the target time from switching to the lean injection amount to switching to the rich injection amount when the current injection amount is set to the lean injection amount, and is the current injection amount. When is set to the rich injection amount, it is the target time from switching to the rich injection amount to switching to the lean injection amount. That is, the process of step S7 corresponds to the process of calculating the target value of the switching cycle described above.

The target switching time S is calculated as follows, for example. FIG. 5A is a map defining the relationship between the intake air amount and the target switching time. The horizontal axis shows the intake air amount, and the vertical axis shows the target switching time. FIG. 5B is a map defining the relationship between the EGR rate and the correction coefficient. The horizontal axis shows the EGR rate, and the vertical axis shows the correction coefficient. This correction coefficient is a numerical value of 1 or more having a minimum value of 1. Each map is stored in the ROM of the ECU 60 in advance. The ECU 60 calculates the target switching time S with reference to these maps. Specifically, the target switching time obtained from the intake air amount with reference to the map of FIG. 5A is multiplied by the correction coefficient obtained from the EGR rate with reference to FIG. 5B, and the time obtained by this is finally obtained. It is calculated as a target switching time S. The intake air amount can be obtained based on the detected value of the air flow meter 15, and the EGR rate can be calculated based on the opening degree of the EGR valve 52.

In the map of FIG. 5A, it is specified that the target switching time becomes shorter as the intake air amount increases. The reason for this is that as the amount of intake air increases, the flow rate of the exhaust gas supplied to the air-fuel ratio sensor 33 increases, so that the rate of change of the output voltage of the air-fuel ratio sensor 33 can be sufficiently changed within a short period of time. Is. In the map of FIG. 5B, it is specified that the correction coefficient increases as the EGR rate increases. The reason for this is that as the EGR rate increases, it takes a longer time for the air-fuel ratio of the exhaust gas caused by the set injection amount to match the air-fuel ratio of the exhaust gas recirculated. The maps of FIGS. 5A and 5B are defined based on the experimental results, and as described above, the target is such that the injection amount can be switched when the air-fuel ratio of the exhaust gas reaches the desired air-fuel ratio. The switching time S is set. In other words, when the exhaust gas recirculation is executed, that is, when the EGR rate is set to other than 0%, the target switching time S is at least the injection amount after the injection amount is switched. It is preferable that the length is longer than the time until a part of the exhaust gas resulting from the above is returned to the intake pipe 10 via the EGR pipe 50 and mixed with the exhaust gas newly generated by the fuel injection.

The method of calculating the target switching time S is not limited to the above method. FIG. 5C is a three-dimensional map that defines the relationship between the intake air amount, the EGR rate, and the target switching time. In this way, the target switching time may be calculated with reference to the three-dimensional map of FIG. 5C. In the map of FIG. 5C, it is specified that the target switching time becomes shorter as the intake intake amount increases, and the target switching time becomes longer as the EGR rate increases. Further, the target switching time S may be calculated by an arithmetic expression instead of such a map. Further, for example, the target switching time may be calculated according to the rotation speed of the engine 20, the load factor, and the EGR ratio.

Returning to FIG. 4, the ECU 60 determines whether or not the time s is equal to or longer than the target switching time S (step S9). If No in step S9, the processes after step S1 are executed again. If Yes in step S9, the ECU 60 executes a process for switching the injection amount (step S11). Specifically, when it is set to the rich injection amount, it is set to the lean injection amount, and when it is set to the lean injection amount, it is set to the rich injection amount. Next, the ECU 60 clears the counting time s (step S13), counts the number of times the injection amount is switched m (step S15), and determines the output voltage measured in step S5 before the injection amount is switched. The rate of change is stored (step S17).

Next, the ECU 60 determines whether or not the number of times of switching m is equal to or greater than a predetermined number of times (step S19). The predetermined number of times is a predetermined number of times suitable for abnormality diagnosis. If No in step S19, the processes after step S1 are executed again. If Yes in step S19, the ECU 60 executes the normal / abnormal determination process (step S21). With the above control, it is possible to suppress a decrease in the accuracy of the abnormality diagnosis of the air-fuel ratio sensor 33 even if the exhaust gas is recirculated.

In the above embodiment, the abnormality diagnosis is performed based on the rate of change of the output voltage of the air-fuel ratio sensor 33, but the method of abnormality diagnosis is not limited to this. For example, the abnormality diagnosis may be performed based on the locus length and area of the output voltage. If the difference between the locus length of the output voltage of the air-fuel ratio sensor to be diagnosed and the locus length of the output voltage of the normal air-fuel ratio sensor is small, it is diagnosed as normal, and if the difference is large, it can be diagnosed as abnormal. Also, when the difference between the area surrounded by the output voltage of the air-fuel ratio sensor to be diagnosed and the output voltage of the stoichiometric sensor and the area surrounded by the output voltage of the normal air-fuel ratio sensor and the output voltage of the stoichiometric engine is small. Is diagnosed as normal, and if the difference is large, it can be diagnosed as abnormal. When an abnormality is diagnosed using the trajectory length or area, the trajectory length or area in the normal state may be changed according to the EGR rate. As described above, even in the case of abnormal diagnosis based on the rate of change of the output voltage of the air-fuel ratio sensor 33, the rate of change of the output voltage in the normal state, which is a reference, may be changed according to the EGR rate. ..

The control of this embodiment can be applied to a gasoline engine or a diesel engine. It can also be applied to the engine of a hybrid vehicle. Further, the present invention is not limited to the air-fuel ratio sensor, and may be applied to an oxygen concentration sensor. Both the air-fuel ratio sensor and the oxygen concentration sensor are examples of gas sensors. The gas sensor may be a sensor whose output value changes according to the air-fuel ratio of the exhaust gas. Further, in the above embodiment, an example in which only the port injection valve 12 is provided is shown, but the present invention is not limited to this, and an engine having only an in-cylinder injection valve may be used, or an in-cylinder injection valve and a port may be provided. The engine may be provided with both injection valves. Similarly, when both the in-cylinder injection valve and the port injection valve are provided, the injection amounts of both injection valves are switched so that the air-fuel ratio of the exhaust gas increases or decreases at the time of abnormality diagnosis.

Although the examples of the present invention have been described in detail above, the present invention is not limited to such specific examples, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

12-port injection valve (fuel injection valve)
33 Air-fuel ratio sensor (gas sensor)
50 EGR tube (EGR device)
52 EGR valve (EGR device)
60 ECU (Gas sensor abnormality diagnostic device)

Claims (1)

The fuel injection amount of the fuel injection valve is increased or decreased in a predetermined cycle so that the air-fuel ratio of the exhaust gas flowing through the exhaust passage of the engine increases or decreases, and the gas sensor becomes abnormal according to the output value of the gas sensor provided in the exhaust passage. It is a gas sensor abnormality diagnosis device for diagnosis.
An EGR device is provided to return a part of the exhaust gas flowing through the exhaust passage to the intake passage of the engine.
When the abnormality diagnosis of the gas sensor is executed when the exhaust gas is recirculated by the EGR device, the cycle is lengthened as compared with the case where the exhaust gas is not recirculated by the EGR device. Gas sensor abnormality diagnosis device to be set.

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