JPS63134842A - Failure diagnostic device for exhaust gas recirculation equipment - Google Patents

Abstract

PURPOSE:To prevent any misjudgement due to a non-injection or an excessive injection by judging that the exhaust gas recirculation equipment is defective when the detection values sensored by an exhaust gas temperature sensor installed in the exhaust gas recirculating path are below a specified value even if the fuel-injection system is normally operated. CONSTITUTION:Detection values sensored by an air flow meter 6, an engine speed sensor 22, an O2 sensor 17, and a throttle switch 18 for detecting an idle opening, etc. are inputted to a control circuit 10 with which air-fuel ratio feedback corrections are carried out depending on the operating conditions of a fuel injection system. When the throttle switch 18 is ON and the air-fuel ratio feedback correction factor continues to be at the upper or lower limit for more than a preset time, the fuel injection system is judged to be abnormal. And when the fuel injection system is abnormal, a water temperature is above about 80 deg.C, an engine speed is in the specified range, Q/N (Q: intake air flow rate; N: engine speed) is less than the specified level and an intake air flow rate is more than the specified rate and further if the temperature detected by an exhaust gas temperature sensor 17 installed downstream EGR control valve 9 in an exhaust gas reflux path 8 is below the specified limit, an alarm lamp is made to light.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a failure diagnosis device for an exhaust gas recirculation system.

[Conventional technology]

Exhaust gas recirculation (
EGR devices are known in which exhaust gas is recirculated into the intake passage via a passage (hereinafter referred to as EGR). In such an EGR device, an EGR control valve is usually provided in the EGR passage, and the amount of EGR gas to be supplied into the intake passage is controlled by the EGR flI3 control valve. However, if the EGR control valve malfunctions or becomes clogged,
There are cases where the supply of GR gas continues to stop, and if this is left as is in such a case, a problem arises in that a large amount of NOx continues to be emitted. Also, like this, E
Even if the supply of GR gas has stopped, the driver will not be aware of this.Therefore, in order to determine the failure of the EGR device, an exhaust gas temperature sensor is placed in the EGR passage downstream of the EGR control valve. There is a known failure diagnosis device that determines that the EGR device is malfunctioning when the temperature in the EGR passage downstream of the EGR control valve does not rise above a certain temperature during an operating state in which the EGR control valve should be recirculated. Utility Model Application No. 49-64623 or Utility Model Application No. 50-6722
(See Publication No. 0). This fault diagnosis method utilizes the fact that the temperature within the EGR gas passage increases when EGR gas is recirculated.

[Problem that the invention seeks to solve]

However, for example, if the EGR passage is branched from the exhaust manifold branch pipe of a specific cylinder among multiple cylinders, and fuel injection from the fuel injection valve of that specific cylinder stops, or if the fuel injection of that specific cylinder If an abnormally large amount of fuel is injected from the valve and a misfire occurs, the exhaust gas salt discharged into the exhaust manifold pipe of that particular cylinder will be low, and this low-temperature exhaust gas will enter the EGR passage circuit. It will be done.

As a result, there is a problem in that even if the EGR device is operating normally, it may be misdiagnosed that the EGR device is malfunctioning.

[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 in FIG.
In a fault diagnosis device configured to determine a failure of an exhaust gas recirculation device from an output signal of a first determination device 100, a first determination device 100 determines whether or not there is an abnormality in the fuel injection system; A second determination means 101 is provided which determines that the exhaust gas recirculation device is malfunctioning when the temperature detected by the exhaust gas temperature sensor 17 is lower than a predetermined temperature.

〔Example〕

Referring to FIG. 2, 1 is the engine body, 2 is the exhaust manifold, 3 is the intake manifold, 4 is the intake duct, 5 is the throttle valve provided in the intake duct 4, 6 is the air 7o-meter, 7a, 7b , 7c.

7d is a fuel injection valve attached to each branch pipe of the intake manifold 3; 8 is a branch pipe of the exhaust manifold 2 and the intake manifold 3;
9 indicates an EGR control valve provided in the EGR passage 8, and 10 indicates an electronic control unit, and the exhaust gas in the exhaust manifold 2 passes through the EGR passage 8 and EGR control valve 9 to It is fed into the manifold 3.

The electronic control unit 10 consists of a digital computer with ROMs interconnected by a bidirectional bus 11.
(read-only memory) 12, RAM (random access memory) 13, CPU (microprocessor) 1
4, an input port 15 and an output port 16.

An exhaust gas temperature sensor 17 is disposed in the EGR passage 8 downstream of the EGR control valve 9, and this exhaust gas temperature sensor 17
It is connected to input port 15 via converter 17a.

Air flow meter 6 generates an output voltage proportional to the amount of intake air, and air flow meter 6 is connected to input port 15 via AD converter 6a.

A throttle switch 18 is connected to the throttle valve 5 to detect whether or not the throttle valve 5 is at an idling opening, and this throttle switch 18 is connected to an AD converter 18a.
It is connected to input port 15 via. Further, a water temperature sensor 19 for detecting engine cooling water temperature is attached to the engine body 1, and this water temperature sensor 19 is connected to the input port 15 via an AD converter 19a. Also, exhaust manifold 2
An oxygen concentration detector 20 is attached to the oxygen concentration detector 20 , and this 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 volt when the air-fuel mixture supplied into the engine cylinder is lean and the exhaust gas is in an oxidizing atmosphere. When the exhaust gas is in a reducing atmosphere, an output voltage of about 0.9 volts is generated. The output voltage of the oxygen concentration detector 20- is compared with a reference voltage of about 0.45 volts in a comparator 21, and the comparator 21 outputs a lean signal when the air-fuel mixture is lean, and a lynch signal when the air-fuel mixture is rich. Input port 15
send to. Note 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 power boat 16 is connected on the one hand via a respective drive circuit 26 to the corresponding fuel injection valve 7 and on the other hand via a drive circuit 27 to a warning lamp 28 .

FIG. 3 shows a routine for executing failure diagnosis of the EGR device. The routine shown in FIG. 3 is executed by interrupts at fixed time intervals.

Referring to FIG. 3, first, in step 30, it is determined from the output signal of the water temperature sensor 19 whether the engine cooling water temperature T is 80°C or higher, and if T>80°C, the process proceeds to step 31. In step 31, from the output signal of the rotation speed sensor 22, the engine rotation speed N is 200Or, p, m<N.
It is determined whether or not it is in the range of <400Or, p, m,
Engine speed N is 200Or, p, m < N < 400
If it is within the range of 0r, p, and m, the process advances to step 32. In step 32, the air flow meter 6 representing the intake air iQ
A rotation speed sensor 2 representing the output signal of the engine and the engine rotation speed N
From the output signal of 2, the amount of intake air taken per cylinder Q/
It is determined whether N is smaller than 0.712/rev, and if Q/N<0.7J/rev, the process proceeds to step 33. In step 33, it is determined from the output signal of the air flow meter 6 whether the intake air iQ is greater than 40 nr/h, and if Q>4On(/h, the process proceeds to step 34.T>80°C and 200Or, p, m<N<
4000r, p, m and Q/N < 0.71
/rev Big Q > 40m/h driving condition is EGR
This is the operating state in which gas recirculation should occur, and therefore EGR
Step 3 when the operating condition requires gas recirculation.
Proceed to step 4.

In step 34, it is determined whether the flag x INJ is 1 or not, that is, whether or not the flag XINJ is set.This flag XINJ will be explained in detail later, but when an abnormality occurs in the fuel injection system, it is determined If the fuel injection system is normal, it will be reset. Therefore, EGR
When the operating state is such that gas should be recirculated and the fuel injection system is normal, the process proceeds to step 35. In step 35, it is determined whether the temperature THG detected by the exhaust gas temperature sensor 17 is lower than a predetermined constant temperature To. If THG<To, proceed to step 36 and output the data that should cause the warning lamp 28 to turn on to the output port 16; if THG2TO, proceed to step 37 and output the data that should cause the warning lamp 28 to turn off to the output port 16. do. If there is an abnormality in the fuel injection system, the process does not proceed to step 35, so in this case, it is not determined whether the EGR system is abnormal or not, and therefore the warning lamp 28 is turned on only when the EGR system is abnormal. You will be forced to do so.

On the other hand, all the fuel injection valves 7a, 7b, 7c.

7d is operating normally and feedback control is being performed to bring the air-fuel ratio to the stoichiometric air-fuel ratio, the output voltage of the oxygen concentration detector 20 changes slowly as shown by the broken line in FIG. At this time, the comparator 21 alternately generates a lean signal and a rich signal in a relatively long period. However, if, for example, the operation of the fuel injection valve 7d is stopped, only air is discharged to the exhaust manifold branch pipe 2d of the cylinder equipped with the fuel injection valve 7d, so that air is intermittently discharged into the exhaust manifold 2. It turns out.

As a result, the exhaust gas around the oxygen concentration detector 20 becomes a reducing atmosphere or an oxidizing atmosphere in a rapid cycle, so the output signal of the oxygen concentration detector 20 oscillates violently as shown by the solid line in FIG. As a result, comparator 21
outputs a lean signal and a rich signal alternately at a fast cycle. Therefore, by monitoring the output signal of the oxygen concentration detector 20, that is, the generation cycle of the lean signal and the rich signal, which are the output signals of the comparator 21, it can be determined whether or not any of the fuel injection valves has failed. On the other hand, when the supply of fuel from the fuel injection valve 7d is stopped, low-temperature air is discharged into the exhaust manifold branch pipe 2d, and therefore low-temperature gas is sent into the EGR passage 8, so that the EGR control valve 9 is activated. Even if the EGR device is operating normally, it is misdiagnosed that the EGR device has failed. Therefore, when the generation cycle of the lean signal and the rich signal becomes short, failure diagnosis of the EGR device is interrupted to prevent misdiagnosis.

4 and 5 show a routine for determining whether the fuel supply operation of the fuel injection valve has stopped. FIG. 4 shows the main routine performed at every predetermined crank angle. Referring to FIG. 4, first, in step 40, it is determined whether a lean signal was generated in the previous processing cycle. If a lean signal is being generated, the process proceeds to step 41, where it is determined whether a rich signal is currently being generated. If a rich signal is currently being generated, the process proceeds to step 42, where the skip number C5kip is incremented by one. On the other hand, if a rich signal was generated in the previous processing cycle, the process proceeds from step 40 to step 43, where it is determined whether a lean signal is currently generated. If a lean signal is currently being generated, the process proceeds to step 42, where the skip number (:5kip) is incremented by 1.

In other words, the skip number C5kip increases by 1 every time there is a change from a Sochi signal to a lean signal or from a lean signal to a rich signal.
is incremented by

Figure 5 shows the number of skips C5 determined by the routine in Figure 4.
A routine for executing failure diagnosis of a fuel injection system using kip is shown. This routine is executed by interrupts at regular intervals.

- Referring to FIG. 5, first, in step 50, it is determined whether the count value Cfail is greater than or equal to a certain value A, and if Cfail<A, the process proceeds to step 51, where the count value Cfail is incremented by 1. . When Cfail≧A, that is, when a predetermined period of time has elapsed, the process proceeds to step 52 and the skip number C5k is reached.
It is determined whether ip is 10 or more. That is, it is determined whether the signal has changed from a lean signal to a rich signal or from a rich signal to a lean signal ten or more times during a certain elapsed time. When the injection action of any fuel injection valve stops, the skip number C5kip becomes 10 or more. C5k
If it is ip210, proceed to step 53 and set the flag XrN.
J is set. When the flag XINJ is set, the failure diagnosis of the EGR device is stopped as described above.

Next, in step 54, the count and the number of skips Ck
IP is reset together. On the other hand, when it is determined in step 52 that C5kip<10, the process proceeds to step 55, where it is determined whether the number of skips C5kip is 6 or less. If C5kip<6, the fuel injection system has not failed, and therefore step 56 is executed in this case.
Then the flag XINJ is reset. Therefore, in this case, failure diagnosis of the EGR device is started. On the other hand, C5
If kip>5, the flag XINJ is maintained as is. Therefore, if the flag XINJ is set, it remains set; if it is reset, it remains reset.

Next, consider a case where, for example, the tip of the needle of the fuel injection valve 7d is clogged with dirt, and as a result, the needle does not close completely and a large amount of fuel is supplied. In this case, the cylinder equipped with the fuel injection valve 7d will misfire, resulting in a decrease in the exhaust gas salt from this cylinder.

This low-temperature exhaust gas is then sent into the EGR passage 8, causing a misdiagnosis.

Normally, in a fuel injection control device, the basic fuel injection time τ required to bring the air-fuel mixture to the stoichiometric air-fuel ratio is calculated from the intake air amount and engine speed, and the feedback correction coefficient is calculated from the output signal of the oxygen concentration detector 20. The actual fuel injection time is determined by multiplying τ by FAF. Since the basic fuel injection time τ is originally determined so that the mixture has the stoichiometric air-fuel ratio, the feedback correction coefficient F
AF changes around 1.0 as shown by E in FIG. Therefore, FAF usually does not become less than 0.75, and therefore, when FAF becomes smaller than 0.75, FAF is maintained 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 amount of injected fuel, and eventually the FAF becomes smaller as shown by G in Figure 8.
AF is maintained at 0.75. Therefore, if FAF remains at 0.75 for a certain period of time, it can be determined that one of the fuel injection valves is malfunctioning, and at this time E
Avoid diagnosing the failure of the GR device.

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

Referring to FIG. 6, first, in step 6o, it is determined whether or not the throttle switch 18 is on, that is, whether or not the throttle valve 5 is at an idling opening. When the throttle valve 5 is not at the idling opening, the process proceeds to step 61 and the count value Cfail is reset. On the other hand, when the throttle valve 5 is at the idling opening, the process proceeds to step 62, where it is determined whether the feedback correction coefficient FAF is 0.75. When the throttle valve 5 is at the idling opening, the fuel captured by the canister (not shown) is supplied into the intake duct 4, and the air-fuel mixture is not enriched, so the FAF is stable. It is then determined whether FAF is 0.75 when the throttle valve 5 is at an idling opening.

If F A F = 0.75, the process proceeds to step 63, where it is determined whether the count value Cfail is 10 or more, and if Cfail<10, the process proceeds to step 64, where the count value Cfail is incremented by 1. .

When Cfail becomes 210, that is, F A F =0.7
5 continues for a certain period of time, the process proceeds to step 65, and the flag
INJ is set, and therefore the failure diagnosis of the EGR device is stopped at this time. On the other hand, F A F −0,7
If it is determined that FAF is not 5, the process 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 failure in the fuel injection system, and the process proceeds to step 67, where the flag XINJ is reset. Therefore, at this time, failure diagnosis of the EGR device is started. When F A F < 0.9, flag XIN
J is maintained as is.

Note that it is possible to detect that the injection action from any of the fuel injection valves has stopped using a similar method.

However, in this case, the determination is made based on whether the FAF is maintained at a predetermined upper limit value, for example 1.25, for a certain period of time or more.

〔Effect of the invention〕

It is possible to completely avoid misdiagnosing that the EGR device is malfunctioning when the fuel injection system is malfunctioning. Therefore, there is no need to replace the EGR device even though it is normal.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] In a failure diagnosis device that includes an exhaust gas temperature sensor disposed in an exhaust gas recirculation passage and determines a failure of an exhaust gas recirculation device from the output signal of the exhaust gas temperature sensor, it is possible to determine whether or not there is an abnormality in the fuel injection system. and determining that the exhaust gas recirculation device is malfunctioning when the fuel injection system is normal and the temperature detected by the exhaust gas temperature sensor is lower than a predetermined temperature. A failure diagnosis device for an exhaust gas recirculation device, comprising: