JPH0819882B2 - Exhaust gas recirculation device failure diagnosis device - Google Patents

Description

The present invention relates to a failure diagnostic device for an exhaust gas recirculation device.

[Conventional technology]

An EGR device is known in which exhaust gas is recirculated into an intake passage through an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to reduce NOx in the exhaust gas. In such an EGR device, an EGR control valve is usually installed in the EGR passage to
The control valve controls the amount of EGR gas to be supplied into the intake passage. However, there are cases where the EGR control valve fails or is clogged, and the supply of EGR gas continues to stop. In such a case, if this is left as it is, a large amount of NOx continues to be emitted.
Further, even if the supply of EGR gas is stopped in this way, the driver does not know that. Therefore, in order to judge such a failure of the EGR device, an exhaust gas temperature sensor is arranged in the EGR passage downstream of the EGR control valve, and the EGR passage downstream of the EGR control valve is in an operating state where the EGR gas should be recirculated. A failure diagnosis device is known in which it is determined that the EGR device is out of order when the temperature of the vehicle does not rise above a certain temperature.
49-64623 or Japanese Utility Model Laid-Open No. 50-67220). This fault diagnosis method is E when EGR gas is recirculated.
The fact that the temperature inside the GR gas passage rises is used.

[Problems to be solved by the invention]

However, for example, when the EGR passage is branched from the exhaust manifold branch pipe of a specific cylinder of the multi-cylinder, the fuel injection from the fuel injection valve of the specific cylinder is stopped, or the fuel injection of the specific cylinder is stopped. When an abnormally large amount of fuel is injected from the valve and misfiring occurs, the temperature of the exhaust gas discharged into the exhaust manifold branch pipe of the specific cylinder becomes low, and this low temperature exhaust gas is sent into the EGR passage. .
As a result, there is a problem that even if the EGR device is operating normally, it is misdiagnosed as a failure of the EGR device.

[Means for solving problems]

In order to solve the above problems, according to the present invention, as shown in the block diagram of the invention of FIG. 1, fuel injection valves 7a, 7b, 7c, 7d are provided for each cylinder, and an exhaust manifold 2 collecting portion is provided. The air-fuel ratio sensor 20 is arranged in the air-fuel ratio sensor 20 to control the fuel injection amount from the fuel injection valves 7a, 7b, 7c, 7d so that the air-fuel ratio becomes a predetermined air-fuel ratio based on the output signal of the air-fuel ratio sensor 20. In the above multi-cylinder internal combustion engine, one of the branch pipes 2d of the exhaust manifold 2 and the intake passage are connected by the exhaust gas recirculation passage 8, and one of the exhaust manifold branch pipes 2d is connected via the exhaust gas recirculation passage 8. The exhaust gas temperature sensor 17 for detecting the temperature of the recirculated exhaust gas recirculated from the intake air passage to the intake passage is further provided, and one of the fuel injection valves 7a, 7b, 7c, based on the output signal of the air-fuel ratio sensor 20. A first judging means 100 for judging whether or not the injection action from 7d is abnormal, Fuel injection valve 7a,
When the injection action from 7b, 7c, 7d is normally performed and the temperature detected by the exhaust gas temperature sensor 20 is not in a predetermined temperature state, it is determined that the exhaust gas recirculation device is out of order. The second judging means 200 is provided.

〔Example〕

Referring to FIG. 2, 1 is an engine body, 2 is an exhaust manifold, 3 is an intake manifold, 4 is an intake duct, 5 is a throttle valve provided in the intake duct 4, 6 is an air flow meter, and 7a, 7b, 7c. , 7d are fuel injection valves attached to the respective branch pipes of the intake manifold 3, and 8 is a branch pipe 2d of the exhaust manifold 2.
An EGR passage communicating between the intake manifold 3 and the intake manifold 3, 9 an EGR control valve provided in the EGR passage 8, 10 an electronic control unit, respectively, and exhaust gas in the exhaust manifold 2 receives the EGR passage 8
And through the EGR control valve 9 into the intake manifold 3.

The electronic control unit 10 is composed of a digital computer, and has a ROM (read only memory) 12, a RAM (random access memory) 13, a CPU (microprocessor) 14, and an input port 15 which are connected to each other by a bidirectional bus 11.
And an output port 16. EGR control valve 9 EGR downstream
An exhaust gas temperature sensor 17 is arranged in the passage 8, and the exhaust gas temperature sensor 17 is connected to the input port 15 via the AD converter 17a. The air flow meter 6 generates an output voltage proportional to the intake air amount, and the air flow meter 6 is connected to the input port 15 via the AD converter 6a. A throttle switch 18 for detecting whether or not the throttle valve 5 is at an idling opening is connected to the throttle valve 5, and the throttle switch 18 is connected to an input port 15 via an AD converter 18a.
Connected to. Further, a water temperature sensor 19 for detecting the engine cooling water temperature is attached to the engine body 1, and the water temperature sensor 19
It is connected to the input port 15 via the AD converter 19a. An oxygen concentration detector 20 is attached to the collecting portion of the exhaust manifold 2, and the oxygen concentration detector 20 is connected to the input port 15 via a comparator 21. The oxygen concentration detector 20 generates an output voltage of about 0.1 V when the air-fuel mixture supplied to the engine cylinder is lean and the exhaust gas is in an oxidizing atmosphere, and the air-fuel mixture supplied to the engine cylinder is too rich. Therefore, when the exhaust gas is in a reducing atmosphere, an output voltage of about 0.9 V is generated. The output voltage of the oxygen concentration detector 20 is compared with a reference voltage of about 0.45 V in the comparator 21, which outputs a lean signal when the mixture is lean and a rich signal when the mixture is rich.
Send to. It should be noted that the input port 15 is further connected to a rotation speed sensor 22 that generates an output signal proportional to the engine rotation speed. The output port 16 is connected on the one hand to the corresponding fuel injection valve 7 via a respective drive circuit 26 and on the other hand to a warning lamp 28 via a drive circuit 27.

FIG. 3 shows a routine for executing a failure diagnosis of the EGR device. The routine shown in FIG. 3 is performed by interruption at regular intervals.

Referring to FIG. 3, first, at step 30, it is judged from the output signal of the water temperature sensor 19 whether or not the engine cooling water temperature T is 80 ° C. or higher. If T> 80 ° C., the routine proceeds to step 31. In step 31, it is judged from the output signal of the engine speed sensor 22 whether the engine speed N is in the range of 2000r.pm <N <4000r.pm, and the engine speed N is 2000r.pm <N <4000.
If it is within the rpm range, proceed to step 32. In step 32, the intake air amount Q / N per cylinder is smaller than 0.7 l / rev from the output signal of the air flow meter 6 indicating the intake air amount Q and the output signal of the rotation speed sensor 22 indicating the engine speed N. It is determined whether or not, and if Q / N <0.7 l / rev, the process proceeds to step 33. In step 33, air flow meter 6
It is determined whether the intake air amount Q is larger than 40 m ³ / h from the output signal of Q. If Q> 40 m ³ / h, the routine proceeds to step 34.
T> 80 ° C and 2000r.pm <N <4000r.pm and Q / N <
The operating state in which 0.7 l / rev and Q> 40 m ³ / h is the operating state in which the EGR gas recirculation should be performed. Therefore, when the operating state in which the EGR gas recirculation is performed, the process proceeds to step 34.

At step 34, it is judged if the flag XINJ is 1, that is, if the flag XINJ is set. The flag XINJ is set when an abnormality occurs in the fuel injection system, which will be described in detail later, and is reset if the fuel injection system is normal. Therefore, when the EGR gas is in an operating state in which it should be recirculated and the fuel injection system is normal, the routine proceeds to step 35. In step 35, exhaust gas temperature sensor
The temperature THG detected by 17 is the predetermined constant temperature T
It is determined whether it is lower than o. If THG <To, proceed to step 36 to output the data for turning on the warning lamp 28 to the output port 16, and if THG To, proceed to step 37 to output to the output port 16 data for turning off the warning lamp 28. To do. If there is an abnormality in the fuel injection system, the routine will not proceed to step 35. In this case, therefore, it is not judged whether the EGR device is abnormal or not. Therefore, the warning lamp 28 lights only when the EGR device is abnormal. Will be punished.

On the other hand, when all the fuel injection valves 7a, 7b, 7c, 7d are operating normally and are feedback-controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, the oxygen concentration detection as shown by the broken line in FIG. The output voltage of the device 20 changes slowly, so that at this time the comparator 21 alternately generates a lean signal and a rich signal with a relatively long period. However, if the operation of the fuel injection valve 7d is stopped, for example, the fuel injection valve
Since only air is discharged to the exhaust manifold branch pipe 2d of the cylinder having 7d, air is intermittently discharged into the exhaust manifold 2. As a result, the exhaust gas around the oxygen concentration detector 20 becomes a reducing atmosphere or an oxidizing atmosphere in a fast cycle, so that the output signal of the oxygen concentration detector 20 vibrates violently as shown by the solid line in FIG. As a result, the comparator 21 alternately outputs the lean signal and the rich signal in a fast cycle. Therefore, by monitoring the output signal of the oxygen concentration detector 20, that is, the generation period of the lean signal and the rich signal, which are the output signals of the comparator 21, it is possible to know whether any of the fuel injection valves has failed. Meanwhile, the fuel injection valve 7d
When the fuel supply from the engine is stopped, the low temperature air is discharged into the exhaust manifold branch pipe 2d, and therefore the low temperature gas is sent into the EGR passage 8, so that the EGR control valve 9 is operating normally. Is mistakenly diagnosed as having a malfunction in the EGR device. Therefore, when the period of generation of the lean signal and the rich signal becomes short, the failure diagnosis of the EGR device is interrupted to prevent misdiagnosis.

4 and 5 show a routine for determining that the fuel supply operation of the fuel injection valve has stopped. FIG. 4 shows a main routine that is performed for each predetermined crank angle. Referring to FIG. 4, first, at step 40, it is judged if the lean signal was generated in the previous processing cycle. When the lean signal is generated, the routine proceeds to step 41, where it is judged whether or not the rich signal is currently generated. If the rich signal is currently generated, the routine proceeds to step 42, where the skip number Cskip is incremented by 1. On the other hand, if the rich signal has been generated in the previous processing cycle, the process proceeds from step 40 to step 43 to determine whether or not the lean signal is currently generated.
If the lean signal is currently generated, the routine proceeds to step 42, where the skip number Cskip is incremented by one. That is,
The skip number Cskip is incremented by 1 each time the rich signal changes to the lean signal or the lean signal changes to the rich signal.

FIG. 5 shows the number of skips Cs obtained in the routine of FIG.
A routine for executing a fuel injection system failure diagnosis using kip is shown. This routine is performed by interruption at regular intervals.

Referring to FIG. 5, first, at step 50, it is judged if the count value Cfail is a certain value A or more, and if Cfail <A, the routine proceeds to step 51, where the count value Cfail
fail is incremented by 1. When it becomes Cfail A, that is, when a predetermined time elapses, step
The routine proceeds to 52, where it is judged if the skip number Cskip is 10 or more. That is, it is determined whether or not the lean signal has changed to the rich signal or the rich signal has changed to the lean signal ten times or more within a certain elapsed time. When the injection action of any of the fuel injection valves is stopped, the skip number Cskip becomes 10 or more. If Cskip10, proceed to step 53 and flag XIN
J is set. When the flag XINJ is set, the failure diagnosis of the EGR device is stopped as described above. Next, at step 54, both the count value Cfail and the skip number Cskip are reset. On the other hand, in step 52, Cskip <1
If it is determined to be 0, the routine proceeds to step 55, where it is determined whether or not the skip number Cskip is 6 or less. Cskip
If it is 6, the fuel injection system has not failed, so in this case, the routine proceeds to step 56, where the flag XINJ is reset. Therefore, in this case, the failure diagnosis of the EGR device is started. On the other hand, if Cskip> 6, the flag XINJ is maintained as it is. Therefore, if the flag XINJ is set, it remains set, and if it is reset, it remains reset.

Next, let us consider a case where dust is clogged in the needle tip portion of the fuel injection valve 7d, and as a result, the needle is not completely closed and a large amount of fuel is supplied. In this case, the cylinder equipped with the fuel injection valve 7d causes a misfire, and as a result, the temperature of exhaust gas from this cylinder decreases. Then, this low-temperature exhaust gas is sent into the EGR passage 8 to cause a misdiagnosis.

In the normal fuel injection control device, the basic fuel injection time τ required to make the air-fuel mixture the stoichiometric air-fuel ratio is calculated from the intake air amount and the engine speed, and the feedback correction coefficient calculated from the output signal of the oxygen concentration detector 20. The actual fuel injection time is determined by multiplying FAF by τ. Since the basic fuel injection time τ is originally determined so that the air-fuel mixture has the stoichiometric air-fuel ratio, the normal feedback correction factor FAF
Varies around 1.0 as shown by E in FIG.
Therefore, the FAF usually does not fall below 0.75, for example.
When becomes less than 0.75, FAF is kept at 0.75. However, if one of the fuel injection valves fails and a large amount of fuel is supplied, the FAF becomes smaller in order to reduce the injected fuel amount, and finally the FAF is maintained at 0.75 as shown by G in FIG. . Therefore, if the FAF is maintained at 0.75 for a certain period of time or longer, it can be determined that one of the fuel injection valves has a failure, and at this time, the EGR device failure diagnosis is not performed.

FIG. 6 shows a routine for executing such a failure diagnosis of the fuel injection system. This routine is executed by interruption at regular time intervals.

Referring to FIG. 6, first, at step 60, it is judged if the throttle switch 18 is on, that is, if the throttle valve 5 is at the idling opening degree.
When the throttle valve 5 is not at the idling opening degree, the routine proceeds to step 61, where the count value Cfail is reset. On the other hand, when the throttle valve 5 is at the idling opening, the routine proceeds to step 62, where the feedback correction coefficient FAF is
It is determined whether or not 0.75. When the throttle valve 5 is at the idling opening, the fuel supplemented by the canister (not shown) is not supplied to the intake duct 4 and the air-fuel mixture is not made rich, so the FAF is stable. For this reason, when the throttle valve 5 is at the idling opening, FA
It is determined whether F is 0.75. FAF ＝
If 0.75, proceed to step 63 and count value Cfail is 10
Whether or not it is above is determined, and if Cfail <10, the routine proceeds to step 64, where the count value Cfail is incremented by one. When Cfail10 is reached, that is, when FAF = 0.75 continues for a certain period of time, the routine proceeds to step 65, where the flag XINJ is set, and therefore, the failure diagnosis of the EGR device is stopped at this time. On the other hand, if it is determined that FAF = 0.75, the routine proceeds from step 62 to step 66, where it is determined whether FAF is 0.9 or more. If FAF 0.9, there is no malfunction in the fuel injection system, so the routine proceeds to step 67, where the flag XINJ is reset. Therefore, at this time, the failure diagnosis of the EGR device is started. When FAF <0.9, the flag XINJ is maintained as it is.

It is possible to detect that the injection action from any of the fuel injection valves is stopped by the same method. However, in this case, FAF has a predetermined upper limit value,
For example, it is determined whether 1.25 has been maintained for a certain period of time or longer.

〔The invention's effect〕

As described above, if an abnormality occurs in the injection action from one of the fuel injection valves, this will appear as a change in the air-fuel ratio,
Therefore, whether an abnormality has occurred in the injection action of any of the fuel injection valves from the output signal of the air-fuel ratio sensor, that is, whether the fuel injection from any of the fuel injection valves has stopped, or whether any of the fuel injection valves has stopped From this, it is possible to determine whether or not an abnormally large amount of fuel has been injected to cause misfire. In this case, the temperature of the exhaust gas discharged from the cylinder in which the fuel injection valve is abnormal decreases, but this exhaust gas mixes with the exhaust gas discharged from the other cylinders in the exhaust manifold collecting portion, so that the exhaust manifold is collected. The temperature of the mixed exhaust gas in the section does not drop so much even if any of the fuel injection valves becomes abnormal. Therefore, when exhaust gas is taken out from the exhaust manifold collecting part and this exhaust gas is recirculated in the intake passage, even if any of the fuel injection valves is abnormal, the recirculated exhaust gas temperature
It is possible to determine whether the R device is operating normally. That is, when exhaust gas is recirculated from the exhaust manifold collecting portion into the intake passage, it is not necessary to stop the EGR device abnormality determination even if an abnormality occurs in any of the fuel injection valves. At this time, if the abnormality determination of the EGR device is stopped, there arises a problem that the chances of the abnormality determination are reduced.

On the other hand, the situation is slightly different when the exhaust gas is taken out from the exhaust manifold branch pipe and is recirculated in the intake passage. That is, in this case, when the fuel injection valve of the cylinder that is taking the exhaust gas has an abnormality, the temperature of the recirculated exhaust gas is likely to be extremely lowered. The possibility of making a wrong decision is extremely high. Therefore, in the present invention, EG
Although the abnormality judgment of the R device is at least eliminated, in order to completely avoid erroneous judgment, the abnormality judgment of the EGR device is made only when the injection action of the fuel injection valve is normal.

[Brief description of drawings]

1 is a block diagram of the present invention, FIG. 2 is an overall view of an internal combustion engine,
FIG. 3 is a flowchart for executing a failure diagnosis of the EGR device, FIG. 4 is a flowchart of a main routine, FIG. 5 is a flowchart for executing a failure diagnosis of the fuel injection system, and FIG. 6 is a flowchart of the fuel injection system. FIG. 7 is a flow chart showing another embodiment for executing the failure diagnosis, FIG. 7 is a diagram showing an output signal of the oxygen concentration detector, and FIG. 8 is a diagram showing a feedback correction coefficient. 2 ... Exhaust manifold, 3 ... Intake manifold, 8 ... EGR passage, 9 ... EGR control valve, 17 ... Exhaust gas temperature sensor.

Claims (1)

[Claims] 1. A fuel injection valve is provided for each cylinder, and an air-fuel ratio sensor is arranged in the exhaust manifold collecting portion so that the air-fuel ratio becomes a predetermined air-fuel ratio based on the output signal of the air-fuel ratio sensor. In a multi-cylinder internal combustion engine configured to control the fuel injection amount from a fuel injection valve, one of the branch pipes of an exhaust manifold and an intake passage are connected by an exhaust gas recirculation passage and the exhaust gas recirculation passage is connected. An exhaust gas temperature sensor for detecting the temperature of the recirculated exhaust gas recirculated from one of the exhaust manifold branch pipes into the intake passage is provided, and one of the fuel injection valves is further provided based on the output signal of the air-fuel ratio sensor. The first determination means for determining whether or not there is an abnormality in the injection action from the fuel injection valve, and the temperature at which the injection action from the fuel injection valve is normally performed and the temperature detected by the exhaust gas temperature sensor is predetermined. The trouble diagnosis device for the exhaust gas recirculation apparatus including an exhaust recirculation system and a second determination means determines that a failure in the absence of the temperature state.