JP2836451B2 - Failure diagnosis device for exhaust gas recirculation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis device for an exhaust gas recirculation device.

[0002]

2. Description of the Related Art EG is provided in a recirculated exhaust gas (hereinafter, referred to as EGR) passage connecting an engine exhaust passage and an engine intake passage.
The EGR control valve is opened when the engine is in an operating state in which the EGR gas is to be recirculated by disposing the R control valve, and the EGR is in the engine operating state in which the recirculation of the EGR gas is to be stopped.
An exhaust gas recirculation device in which a control valve is closed has been conventionally known. In this case, if the EGR gas is supplied when the EGR control valve fails and the recirculation of the EGR gas should be stopped, the combustion deteriorates, and therefore, it is possible to early find out whether or not the EGR control valve has failed. Required.

Therefore, a temperature sensor is disposed in the intake passage immediately downstream of the EGR gas supply port, and the EGR control valve is forcibly closed when the engine is in an operating state in which the EGR gas is to be recirculated. An EGR control valve closing signal is sent, and EG
The temperature between the temperature in the intake passage detected by the temperature sensor immediately before sending the R control valve closing signal and the temperature in the intake passage detected by the temperature sensor after a certain period of time has passed after sending the EGR control valve closing signal. There is known an exhaust gas recirculation device that determines that the operation of an EGR control valve is abnormal when the temperature difference is smaller than a predetermined temperature difference (see Japanese Patent Application Laid-Open No. 62-162761). That is, EG
If the EGR control valve is closed when the R control valve closing signal is sent, the supply of EGR gas into the intake passage stops, so the above-mentioned temperature difference becomes considerably large. Even if the valve closing signal is sent, if the EGR control valve continues to be opened, the EGR gas continues to be supplied into the intake passage, so that the above-mentioned temperature difference hardly occurs. Therefore, it can be determined from the temperature difference whether the EGR control valve has failed.

[0004]

In the case where it is determined whether or not the EGR control valve has failed based on the temperature difference as described above, the EGR control valve is operated when the temperature difference between the normal state and the abnormal state is the largest. If it is determined whether the control valve has failed, it is possible to reliably determine the failure of the EGR control valve while avoiding erroneous determination. By the way, when the EGR control valve is closed, the temperature detected by the temperature sensor starts to decrease. After a while, the temperature is settled down to a certain temperature, and the temperature difference after the temperature is settled becomes the largest. Therefore, the failure of the EGR control valve can be determined as quickly as possible so as not to cause an erroneous determination by determining the failure of the EGR control valve from the temperature difference immediately after the temperature detected by the temperature sensor falls to a certain temperature. .

[0005] However, the time required for the temperature detected by the temperature sensor to reach a constant temperature greatly changes depending on the EGR gas amount before the EGR control valve closing signal is sent and the temperature of the engine body, the intake pipe, and the like. Becomes longer as the EGR gas amount before the EGR control valve closing signal is sent and as the temperature of the engine body, the intake pipe and the like becomes higher. Therefore, when the temperature difference is detected a certain time after the EGR control valve closing signal is sent as in the above-described exhaust gas recirculation device, when the EGR gas amount is large, and when the temperature of the engine body or the like is low. This time has to be considerably longer in consideration of high times.

However, if the time from when the EGR control valve closing signal is sent to when the temperature difference is detected is increased as described above, even if the temperature detected by the temperature sensor falls to a certain temperature in a short time, it is not necessary. Therefore, it is necessary to wait for the detection of the temperature difference for a while, and thus there is a problem that the failure determination of the EGR control valve cannot be promptly performed. Further, if the operation state in which the EGR gas is to be supplied again while waiting for the detection of the temperature difference is established, it is impossible to determine the failure of the EGR control valve.
There is a big problem that it is not possible to immediately determine the failure of the GR control valve.

In the above exhaust gas recirculation system, the EGR
Since the supply of the EGR gas is forcibly stopped in the operation state in which the gas supply is required, there is a problem that the exhaust emission deteriorates.

[0008]

According to the present invention, a recirculation exhaust gas control valve is disposed in a recirculation exhaust gas passage connecting an engine exhaust passage and an engine intake passage. The recirculation exhaust gas control valve is opened when the engine is in the operating state in which exhaust gas is to be recirculated, and the recirculation exhaust gas control valve is closed in the engine operating state in which the exhaust gas recirculation is to be stopped. In the exhaust gas recirculation apparatus, a temperature sensor for detecting a temperature in the recirculation exhaust gas passage and a count value increase and decrease in accordance with the temperature in the recirculation exhaust gas passage when the recirculation exhaust gas valve operates normally. A temperature estimation counter, and when the engine operating state shifts from an operating state in which exhaust gas is to be recirculated to an operating state in which exhaust gas recirculation is to be stopped, the temperature in the recirculated exhaust gas passage immediately before the shift. Migration When the temperature difference from the temperature in the recirculation exhaust gas passage when the count value decreases to a predetermined set value is smaller than the predetermined temperature difference, the operation of the recirculation exhaust gas control valve is abnormal. To judge.

[0009]

[Action] After the engine operating state shifts from an operating state in which exhaust gas is recirculated to an operating state in which exhaust gas recirculation is stopped, the count value representing the temperature in the recirculated exhaust gas passage falls to a set value. Then, the temperature difference is detected, and it is determined whether or not the operation of the recirculation exhaust gas control valve is abnormal based on the temperature difference.

[0010]

Referring to FIG. 1, reference numeral 1 denotes an engine body, 2 denotes an intake valve, 3 denotes an intake branch pipe, 4 denotes a fuel injection valve, 5 denotes an exhaust valve, and 6 denotes an exhaust manifold. Each intake branch pipe 3 is connected to a common surge tank 7, and the surge tank 7 is connected to an intake duct 8.
And an air flow meter 9 to connect to an air cleaner 10. A throttle valve 11 is arranged in the intake duct 8. The inside of the exhaust manifold 6 and the inside of the surge tank 7 are connected to each other via an EGR passage 12, and an EGR control device 13 is arranged in the EGR passage 12.

The EGR control device 13 includes an EGR control valve 1
4 and a modulator 15. EGR control valve 14
Has a negative pressure chamber 17 and an atmospheric pressure chamber 18 separated by a diaphragm 16, and a diaphragm pressing compression spring 19 is inserted into the negative pressure chamber 17. Further, a valve element 21 that controls opening and closing of the valve port 20 is connected to the diaphragm 16.
Further, the EGR control valve 14 has a constant-pressure chamber 22. The constant-pressure chamber 22 is connected to the exhaust manifold 6 via the throttle 23 and the EGR passage 12 on the one hand, and the opening amount is controlled by the valve 21 on the other hand. The surge tank 7 is connected via the valve port 20 and the EGR passage 12.

On the other hand, the modulator 15 is
4, a pressure control chamber 25 and an atmospheric pressure chamber 26 are separated from each other. In the atmospheric pressure chamber 26, a diaphragm pressing compression spring 27 and an air bleed pipe 28 are provided. The upper end of the air bleed tube 28 is connected to the EG via a negative pressure conduit 29 on the one hand.
The throttle 3 is connected to the negative pressure chamber 17 of the R control valve 14,
It is connected to a negative pressure port 32 that opens into the intake duct 8 via a zero and a negative pressure conduit 31. As shown in FIG. 1, this negative pressure port 32 opens into the intake duct 8 upstream of the throttle valve 11 when the throttle valve 11 is at the idling position, while when the throttle valve 11 is opened, the intake duct 8 downstream of the throttle valve 11 is opened. Open inside. An opening 33 is formed at the lower end of the air bleed tube 28 so as to face the diaphragm 24, and the pressure control chamber 25 is connected to the constant pressure chamber 22 via a conduit 34.

A negative pressure control valve 35 having a valve element 36 and a solenoid 37 for driving the valve element 36 is disposed in the negative pressure conduit 29. When the solenoid 37 is deenergized, as shown in FIG.
8 is closed and the atmosphere port 39 is closed, so that at this time the negative pressure chamber 17 of the EGR control valve 14 is connected to the negative pressure port 32 via the negative pressure conduits 29 and 31.
On the other hand, when the solenoid 37 is energized, the valve body 36 closes the valve port 38 and opens the atmosphere port 39,
Therefore, at this time, the negative pressure chamber 17 of the EGR control valve 14 is opened to the atmosphere.

When the solenoid 37 of the negative pressure control valve 35 is deenergized, the throttle valve 11 opens and the EGR control valve 1
When a negative pressure acts on the negative pressure chamber 17 of 4, exhaust gas in the exhaust manifold 6 is supplied into the surge tank 7 via the EGR passage 12. At this time, when the pressure of the exhaust gas sent from the exhaust manifold 6 into the constant pressure chamber 22 through the EGR passage 12 and the throttle 23 becomes slightly higher than a set pressure slightly higher than the atmospheric pressure, the diaphragm 24 of the modulator 15 is compressed by a compression spring. It rises against 27. As a result, the air bleed opening 33 is narrowed by the diaphragm 24, so that the negative pressure in the negative pressure chamber 17 increases. Thus, the valve body 21 rises against the compression spring 19 and the valve port 2
0, the exhaust gas pressure in the constant pressure chamber 22 decreases. When the exhaust gas pressure falls slightly below the above-mentioned set pressure, the amount of air bleed into the air bleed pipe 28 increases because the diaphragm 24 descends, thereby reducing the negative pressure in the negative pressure chamber 17. Become. As a result, since the valve element 21 is lowered by the spring force of the compression spring 19, the opening area of the valve port 20 is reduced, and the exhaust gas pressure in the constant pressure chamber 22 increases again. In this way, the pressure in the constant pressure chamber 22 is maintained at substantially the atmospheric pressure.

[0015] The gauge pressure of the exhaust gas in the exhaust manifold 6 and P _e, the gauge pressure of the exhaust gas of constant pressure chamber 22 P _o
Then, the flow rate Q of the exhaust gas flowing into the constant pressure chamber 22 from the exhaust manifold 6 through the EGR passage 12 and the throttle 23
It is proportional to the square root of (P _e -P _o). However gauge P _o is P _o is substantially becomes zero to equal to the above-mentioned set pressure is approximately atmospheric pressure, thus to exhaust gas flow rate Q in the constant pressure chamber 22 is proportional to the square root of P _e. However Between the intake air quantity Q _a exhaust gas pressure P _e P _e αQ _a ²
Therefore, Q∝Q _a , and the amount of EGR gas Q recirculated into the surge tank 7 is proportional to the amount of intake air Q _a . In other words, the EGR rate is kept substantially constant by the EGR control valve 14 and the modulator 15.

The electronic control unit 40 is composed of a digital computer, and is connected to a read-only memory (ROM) 42, a random access memory (RAM) 43, a CPU (microprocessor) 44, and a power supply connected to each other by a bidirectional bus 41. Backup RAM connected
45, an input port 46 and an output port 47. A water temperature sensor 50 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 50 is input to an input port 46 via a corresponding AD converter 51. The EGR passage 12 is provided between the EGR control valve 14 and the surge tank 7.
Temperature sensor 52 that generates an output voltage proportional to the temperature inside
And the output voltage of the temperature sensor 52 is input to the input port 46 via the corresponding AD converter 51.
An intake air temperature sensor 53 that generates an output voltage proportional to the intake air temperature is arranged upstream of the air flow meter 9, and the output voltage of the intake air temperature sensor 53 is input to the input port 46 via the corresponding AD converter 51. You.

On the other hand, the air flow meter 9 generates an output voltage proportional to the amount of intake air.
The data is input to the input port 46 via the D converter 51. A throttle sensor 54 for generating an output signal indicating the throttle opening is attached to the throttle valve 11, and the output signal of the throttle sensor 54 is input to the input port 46 via the corresponding AD converter 51. Also, the input port 46
Are connected to a speed sensor 55 for generating an output pulse representing the engine speed and a vehicle speed sensor 56 for producing an output pulse representing the vehicle speed. On the other hand, the output port 47 is connected to the solenoid 37 of the negative pressure control valve 35 and the warning light 58 via the corresponding drive circuits 57, respectively.

The negative pressure control valve 35 is provided to control the operation of the EGR control valve 14. First, a control routine of the negative pressure control valve 35 will be described with reference to FIG. This routine is executed by interruption every predetermined time. Referring to FIG. 2, first, step 10 is executed.
At 0, it is determined whether a predetermined time, for example, 2 seconds, has elapsed after the engine was started. If two seconds have not elapsed after the start of the engine, the routine proceeds to step 105, where the negative pressure control valve 35 is turned on. When the negative pressure control valve 35 is turned on, that is, when the solenoid 37 is energized, the negative pressure chamber 1 of the EGR control valve 14
7 is opened to the atmosphere, and thus the EGR control valve 14 is closed. Therefore, at this time, the supply of the EGR gas to the surge tank 7 is stopped. On the other hand, if two seconds have elapsed after the engine is started, the routine proceeds to step 101, where the engine cooling water temperature TW detected by the water temperature sensor 50 becomes a constant temperature, for example, 6
It is determined whether the temperature is higher than 0 ° C. When TW <60 ° C., the routine proceeds to step 105, where the negative pressure control valve 35 is turned on. That is, when the engine cooling water temperature TW is lower than 60 ° C., the negative pressure chamber 17 of the EGR control valve 14 is opened to the atmosphere, and the supply of the EGR gas is stopped.

When TW ≧ 60 ° C., the routine proceeds to step 102, where it is determined whether or not the engine is idling. For example, when the opening of the throttle valve 11 detected by the throttle sensor 54 is the idling opening, it is determined that the engine is in the idling operation. When the engine is idling, the routine proceeds to step 105, where the negative pressure control valve 35
Is turned on, and thus the supply of the EGR gas is stopped. On the other hand, when the engine is not idling, the routine proceeds to step 103, where it is determined whether or not the absorbed air amount Q detected by the air flow meter 9 is larger than a predetermined set value _Qo . This set value Q _o is a function of the engine speed N, as shown in FIG. 3, and increases as the engine speed N increases. When Q < _Qo , that is, when the intake air amount is small, the routine proceeds to step 105, and the supply of the EGR gas is stopped.

On the other hand, when Q ≧ Qo, the _routine proceeds to step 104, where it is determined whether or not the OTP increase for increasing the fuel for preventing the exhaust system from heating is being performed. OT
When the P increase is being performed, the routine proceeds to step 105, where the negative pressure control valve 35 is turned on, and thus the supply of the EGR gas is stopped. On the other hand, when the OTP increase is not performed, the processing routine is completed. That, and after two seconds after engine start, a TW ≧ 60 ° C., rather than the time of idling, a Q ≧ Q _o, and the solenoid 37 of the negative pressure control valve 35 when the OTP boosting is not performed
Is deenergized. At this time, the negative pressure chamber 17 of the EGR control valve 14 is connected to the negative pressure port 32 via the negative pressure conduits 29 and 31. Therefore, at this time, if a negative pressure acts on the negative pressure port 32, the EGR control valve 14 opens, and thus the EGR gas is supplied into the surge tank 7.

FIG. 4 shows the EGR ON region at this time, that is, E
The region where the GR gas is supplied is shown. In FIG. 4, the vertical axis TA indicates the opening of the throttle valve 11, and the horizontal axis N indicates the engine speed. As can be seen from FIG.
Even if the negative pressure chamber 17 of the GR control valve 14 is connected to the negative pressure port 32, the throttle valve opening TA is equal to or more than a certain opening degree, as shown in FIG.
In the embodiment shown in (1), the negative pressure does not act on the negative pressure port 32 unless it becomes 5 ° or more. Therefore, as shown in FIG. 4, the EGR ON region is a region where the throttle valve opening TA is 5 ° or more. On the other hand, when the intake air amount increases, the negative pressure port 3
The negative pressure acting on the 2 decreases, resulting in closing the EGR control valve 14 is in the amount of intake air is less than the upper limit value G _o of FIG.
Therefore, the EGR ON region is a region where the intake air amount is equal to or less than the upper limit value _Go .

When the supply of EGR gas is started, the temperature in the EGR passage 12 between the EGR control valve 14 and the surge tank 7 rises, and when the supply of EGR gas is stopped, the EGR gas is stopped.
Since the temperature in the passage 12 decreases, the temperature in the EGR passage 12 can be estimated from whether the EGR gas is supplied or whether the supply of the EGR gas is stopped. In the present invention, the temperature estimation counter which increases and decreases the count value according to the temperature in the EGR passage 12 has
The method for estimating the temperature in the R passage 12 will now be described with reference to a control routine of a temperature estimation counter shown in FIG. This routine is executed by interruption every predetermined time.

Referring to FIG. 5, first, step 20 is executed.
0, whether the negative pressure control valve 35 is ON, that is, E
It is determined whether or not the supply of the GR gas has been stopped.
When the negative pressure control valve 35 is off, that is, when the EGR gas can be supplied, the routine proceeds to step 201, where it is determined whether or not the engine is in the EGR ON region shown in FIG. When it is in the EGR ON region, the temperature rise amount ΔXC of the EGR passage 12 within the interruption time interval is calculated. The temperature increase ΔXC is a function of the vehicle speed SPD, and decreases as the vehicle speed SPD increases, as shown in FIG. That is, as the vehicle speed SPD increases, the conduit forming the EGR passage 12 is cooled by the traveling wind, so that the temperature increase rate ΔXC decreases as the vehicle speed SPD increases.

Next, at step 203, the temperature rise amount ΔXC is added to the temperature estimation count value XC. Next, at step 204, the estimated temperature count value XC is set to the upper limit value MAX.
Is determined, and when XC ≧ MAX, the routine proceeds to step 205, where XC = MAX. Therefore, as shown in FIG. 7, when the EGR gas is supplied, the temperature estimation counter XC gradually increases, and XC = MAX
Then, XC = MAX is maintained.

On the other hand, if it is determined in step 200 that the negative pressure control valve 35 is on,
When it is determined in step 1 that the EGR gas is not in the EGR ON region, that is, when the supply of the EGR gas is stopped, the routine proceeds to step 206, where the temperature decrease amount ΔY is subtracted from the estimated temperature count value XC. According to experience, the amount of temperature decrease ΔY is not significantly affected by the traveling wind, so that the amount of temperature decrease ΔY is a constant value. Next, at step 207, it is determined whether or not the estimated temperature count value XC has become equal to or less than zero.
When it is 0, the routine proceeds to step 208, where XC = 0.

Therefore, as shown in FIG. 7, when the supply of the EGR gas is stopped, the temperature estimation counter XC gradually decreases, and when XC = 0, XC = 0 is thereafter maintained. Therefore, XC increases and decreases between MAX and 0. The estimated temperature count value XC changes following the temperature in the EGR passage 12, and thus the EGR passage 1
This indicates the temperature in 2 well.

Next, the failure judgment of the negative pressure control valve 35 will be described. The negative pressure control valve 35 is unlikely to cause a failure such that the valve body 36 keeps closing the valve port 38, but may cause a failure such that the valve body 36 keeps closing the atmosphere port 39. If the valve body 36 keeps closing the atmosphere port 39, EG
Since the EGR gas is supplied when the supply of the R gas is to be stopped, the combustion deteriorates. Therefore, such a failure needs to be detected as soon as possible.

FIG. 8 shows a negative pressure control valve opening abnormality detecting routine for detecting that the valve body 36 of the negative pressure control valve 35 keeps closing the atmosphere port 39. Is executed by interruption every predetermined time. Referring to FIG. 8, first, at step 300, the EG at the time of engine start detected by the temperature sensor 52 is detected.
The temperature in the R passage 12 is set to THGSTA. Next, at step 301, it is determined whether or not the operating condition for performing the failure detection is satisfied. That is, the throttle opening TA is 6 ° or more and the engine cooling water temperature TW is 30 ° C ≦
It is determined that the execution condition is satisfied when TW <60 ° C. That is, when TW <60 ° C., as described above, EG
The negative pressure control valve 35 is turned on in order to open the negative pressure chamber 17 of the R control valve 14 to the atmosphere. Therefore, at this time, the throttle opening TA becomes 6 ° C. or more, and the negative pressure acts on the negative pressure port 32. Even so, the supply of EGR gas should continue to be stopped. Therefore, if EGR gas is supplied at this time, the valve body 36 has opened the valve port 38, and thus it can be determined that the negative pressure control valve 35 has failed.

When the execution condition is satisfied, the routine proceeds to step 302, where the temperature THG in the EGR passage 12 detected by the temperature sensor 52 is changed to the temperature T in the EGR passage 12 when the engine is started.
It is determined whether the value is larger than a value obtained by adding HGSTA to a fixed value, for example, 20 ° C. If the supply of the EGR gas is stopped, the temperature THG in the EGR passage 12 becomes 20 ° with respect to the temperature THGSTA in the EGR passage 12 when the engine is started.
Or higher, so THG ≧ THGS
If TA + 20 ° C., it is determined that there is a high possibility that a failure has occurred, and the routine proceeds to step 303. In step 303, the interruption time interval Δt is added to the abnormal count value CA,
Next, the routine proceeds to step 305.

On the other hand, THG <THGSTA + 20
When the temperature is ° C, it is determined that there is a high possibility of normal operation, and the process proceeds to step 304. In step 304, the normal count value C
B, the interruption time interval Δt is added, and then step 3
Go to 05. In step 305, it is determined whether or not the abnormal count value CA has reached a fixed value, for example, 10 seconds or more. CA ≧ 10 seconds, that is, THG ≧ THGSTA + 20 ° C.
If the state becomes more than 10 seconds, it is considered that the negative pressure control valve 35 is abnormal. At this time, the routine proceeds to step 306, where the abnormality flag F is set.

On the other hand, if CA <10 sec, the routine proceeds to step 307, where it is determined whether or not the abnormal count value CA is smaller than a predetermined value, for example, 1 second. CA <1se
In the case of c, the routine proceeds to step 308, where the normal count value C
It is determined whether B is a fixed value, for example, 10 seconds or more. If CA <1 sec and CB ≧ 10 sec, it is considered to be normal.
Then, the abnormality flag F is reset. On the other hand, when 10 sec> CA ≧ 1 sec, or when CA <1 sec and CB <10 sec, it cannot be determined that the operation is normal, and the processing routine is completed.

On the other hand, if the EGR control valve 14 is kept in the open state, the supply of the EGR gas is stopped even when the EGR gas supply is to be stopped.
Gas is supplied and combustion is thus worse. Therefore EG
If a failure occurs such that the R control valve 14 is kept open, it is necessary to detect this early. FIG. 9 shows a method for detecting such a failure of the EGR control valve 14. Next, this method will be described with reference to FIG.

As shown in FIG. 9, the temperature THG in the EGR passage 12 detected by the temperature sensor 52 is EGR.
Is high, that is, when EGR gas is being supplied. Next, when the EGR is turned off, that is, when the supply of the EGR gas is stopped, the temperature sensor 5
2, the temperature THG in the EGR passage 12 starts to decrease. Then, after a while, the temperature in the EGR passage 12 detected by the temperature sensor 52 decreases to a constant temperature THGoff determined by the engine operating state, and then calms down at the constant temperature THGoff. Therefore, if the EGR control valve 14 is closed when the supply of the EGR gas should be stopped, the temperature TH in the EGR passage 12 detected by the temperature sensor 52 immediately before the supply of the EGR gas is stopped.
The temperature difference between GO and the above-mentioned constant temperature THGoff becomes considerably large.

On the other hand, when the EGR control valve 14 is out of order and the supply of EGR gas should be stopped,
When the R control valve 14 continues to be opened, the temperature THG in the EGR passage 12 detected by the temperature sensor 52 becomes THG.
There is almost no change for O. Therefore THGO and TH
If the temperature difference from Goff is larger than a predetermined temperature difference ΔT (FIG. 9), the EGR control valve 14 is operating normally. If the temperature difference between THGO and THGoff is smaller than ΔT, the EGR control valve is 14 is out of order. When the EGR gas temperature increases, the temperature sensor 52
The value of ΔT decreases as THGO increases, as shown in FIG.

As described above, in order to accurately and early detect a failure of the EGR control valve 14, the EGR
After the engine operation state in which gas supply should be stopped, EG
During the normal operation of the R control valve 14, it is necessary to detect the temperature difference between THGO and THGoff immediately after the temperature in the EGR passage 12 reaches the constant temperature THGoff.
However, when the EGR control valve 14 operates normally after the engine operation state in which the supply of the EGR gas should be stopped, the EG
The time T _k (FIG. 9) until the temperature in the R passage 12 reaches THGoff is equal to EG when the EGR gas is supplied.
Since it is greatly affected by the R gas amount, the engine temperature, and the like, it greatly changes depending on the EGR gas amount, the engine temperature, and the like.
Therefore, in the present invention by using the temperature estimated count value XC to estimate the time T _k.

That is, since the estimated temperature count value XC changes following the temperature THG in the EGR passage 12 detected by the temperature sensor 52 as described above, the operation state in which the supply of the EGR gas should be stopped is established. Later, when the temperature estimation count value XC decreases to a predetermined set value, it can be estimated that the time _Tk has elapsed. In the embodiment shown in FIG. 9, the predetermined set value is the lower limit value (= 0) of the estimated temperature count value XC.

FIGS. 11 and 12 show a routine for detecting that the EGR control valve 14 is kept open, and this routine is executed by interruption every predetermined time. Referring to FIGS. 11 and 12, first, at step 400, it is determined whether or not the engine is in the EGR-on region shown in FIG. If it is not in the EGR ON region, the routine proceeds to step 404, where the count value D is set to zero,
Next, the routine proceeds to step 405. On the other hand, when the engine is in the EGR ON region, the routine proceeds to step 401, where the time interruption interval Δt is added to the count value D. Then step 40
In 2, it is determined whether or not the count value D has become larger than a predetermined time, for example, 3 seconds. When D ≦ 3 sec, the process jumps to step 405, and when D> 3 sec, the process proceeds to step 403 where EG detected by the temperature sensor 52 is detected.
The temperature THG in the R passage 12 is set to THGO (FIG. 9).

That is, THG is set to THGO when three seconds have passed since the EGR-on area was set, and thereafter THGO is updated as long as the EGR-on area continues. That is, there is a response delay in the temperature sensor 52, and even when the shift from the EGR off region to the EGR on region and the supply of the EGR gas is started, the THG detected by the temperature sensor 52 does not immediately rise. Therefore, even if the EGR is in the EGR ON region, for a while, the temperature THG detected by the temperature sensor 52 does not accurately represent the temperature in the EGR passage 12, and therefore, three seconds after the shift to the EGR ON region Does not update THGO.

In step 405, it is determined whether or not a detection execution condition for detecting whether or not the EGR control valve 14 remains open is satisfied. In this case, it is determined that the detection execution condition is satisfied when the following three conditions are satisfied. (I) Engine cooling water temperature TW is 100 ° C. or less and intake air temperature THA is 50 ° C. or less, TW ≧ 100 ° C.
Alternatively, if TAH ≧ 50 ° C., the temperature of the engine body is high and the temperature detected by the temperature sensor 52 does not readily decrease even if the supply of the EGR gas is stopped. Therefore, to avoid misjudgment, TW <100 ° C. and THA <50 °
At this time, it is determined that the detection execution condition is satisfied.

(Ii) When the throttle opening TA is a fixed opening, for example, 3 ° or less. As long as the EGR control valve 14 is operating normally, if TA <3 °, the EGR control valve 14 is closed and the supply of EGR gas is stopped.
When the angle is 3 °, it is determined that the detection execution condition is satisfied. (Iii) When it is determined that TA <3 °, when the negative pressure control valve 35 has been turned off in the previous interrupt routine, that is, when the solenoid 37 of the negative pressure control valve 35 has been deenergized. That is, when the supply of the EGR gas is not stopped before TA <3 °, it is determined that the detection execution condition is satisfied.

When it is determined in step 405 that the detection execution condition is satisfied, the process proceeds to step 406, and the temperature difference obtained by subtracting the temperature THG in the EGR passage 12 detected by the temperature sensor 52 from THGO updated in step 403. It is determined whether (THGO-THG) is smaller than a predetermined temperature difference ΔT (FIGS. 9 and 10). When the detection execution condition is satisfied, E
Since the region is the GR-on region to the EGR-off region, the process proceeds from step 400 to step 404.
HGO represents the temperature THG in the EGR passage 12 immediately before shifting from the EGR on region to the EGR off region.

When the EGR control valve 14 is out of order, (THGO-THG) <ΔT, and the EGR control valve 14
Is normal, immediately after the execution condition is satisfied (THGO
−THG) <ΔT, and in these cases, the process proceeds to step 407. In step 407 THGO constant temperature T _o, whether large is determined than, for example, 90 ° C.. That is, when the EGR control valve 14 has failed and the EGR control valve 14 has been kept closed, THGO becomes 9
It is 0 ° C. or less. That is, THGO becomes 90 ° or more when the EGR control valve 14 is operating normally or when the EG
This is when the R control valve 14 is kept open.
Therefore THGO is so as to determine greater or not than T _o to detect whether the left open by step 407 the EGR control valve 14.

[0043] whether the temperature estimated count value XC has become zero proceeds to step 408 when it is judged that THGO ≧ T _o in step 407 is determined. XC =
When it becomes 0, it can be determined that the EGR control valve 14 has been kept open. That is, before XC = 0, (THG
If (O−THG) ≧ ΔT, the process does not proceed to step 408, so that it is determined that XC = 0 in step 408 because XC =
When it is 0, it means that (THGO-THG) <ΔT. Therefore, when XC = 0 in step 408, it can be determined that the EGR control valve 14 is kept open. Therefore, basically, the failure of the EGR control valve 14 can be determined up to step 408.

In the embodiment according to the present invention, when it is determined in step 408 that the EGR control valve 14 has failed, it is determined again by another method whether or not the EGR control valve 14 has failed. When it is determined that the EGR control valve 14 has failed again by the above method, it is finally determined that the EGR control valve 14 has failed.

This other method is a method for judging the failure of the EGR control valve 14 from the fluctuation of the engine speed during the engine idling operation. That is, if the EGR control valve 14 is operating normally, the supply of the EGR gas is stopped during the engine idling operation, but if the EGR control valve 14 is kept open, the EGR gas is supplied during the engine idling operation. . If the EGR gas is supplied during the engine idling operation, the combustion deteriorates and misfires occur, so that the fluctuation of the engine speed becomes large. Therefore, it is possible to determine whether or not the EGR control valve 14 is out of order. .

That is, when it is determined in step 408 that XC = 0, the routine proceeds to step 409, where it is determined whether or not the count value CC is longer than a predetermined time, for example, 22 seconds. It is determined whether or not the misfire count value CM is equal to or greater than a predetermined value _CMo . These count values CC and _CMo are shown in FIG.
3 is controlled in the routine shown in FIG. 3, and therefore, the routine shown in FIG. 13 will be described first. This routine is executed by interruption every predetermined time.

Referring to FIG. 13, first, in step 5
The vehicle speed SP detected by the vehicle speed sensor 56 at 00
It is determined whether D is equal to or higher than a constant speed, for example, 15 km / h. Step 50 when SPD <15 km / h
The program proceeds to 1 to determine whether or not the vehicle is idling. In this case, when the opening of the throttle valve 11 is the idling opening, it is determined that the engine is in the idling operation. During idling operation, the routine proceeds to step 502, where it is determined whether or not the vehicle speed SPD is zero. When the vehicle is not idling, or when the vehicle speed SPD is not zero even during idling, the routine proceeds to step 512, where the count value CC is made zero, and then step 513.
And the misfire count value CM is set to zero.

On the other hand, during idling operation, the vehicle speed S
When PD = 0, the routine proceeds to step 503, where the time interruption interval Δt is added to the count value CC. Next, at step 504, when the count value CC is 2 seconds or more and 2
It is determined whether it is less than 2 seconds. 2sec ≦ CC ≦ 2
When 2sec absolute value ΔN of the difference between the engine speed N ₁ at the time willing engine speed N and the last at the time of current interruption interrupt to step 505, i.e., the engine speed fluctuation amount ΔN is calculated. Next, at step 506 the fluctuation amount .DELTA.N whether large is determined than a certain value .DELTA.N _o.
At the time of ΔN> ΔN _o the procedure proceeds to step 507, ΔN ≦
At the time of the ΔN _o jumps to step 508. In step 507, the misfire count value CM is incremented by one. Next, at step 508, the flag Z is set, and then the processing cycle is completed. That is, in steps 503 to 507, 2sec ≦ CC ≦ 22se
A misfire count value CM representing the number of misfires occurring during the period c, that is, for 20 seconds is calculated. Next, the vehicle is driven, and at step 500, the vehicle speed S
If it is determined that the PD exceeds 15 km / h, step 50 is performed.
Proceeding to 9, it is determined whether the flag Z is set. Step 5 if the flag Z is set
Proceeding to 10, the value of THGO is made zero, then step 51
At 1, the flag Z is reset. That is, as can be seen from the flowchart shown in FIG. 13, when the vehicle is stopped for a predetermined time or more, for example, for two seconds or more in the idling operation state, the flag Z is set, and when the flag Z is set, the vehicle speed SPD is reduced to 15 km / h thereafter. When it exceeds, THGO is set to zero. This is for the following reason.

That is, after the vehicle stops, the vehicle is driven and the EG
The supply of R gas is started, and then E is again
Even when the operation state shifts to an operation state in which the supply of the GR gas should be stopped, it is determined whether or not the EGR control valve 14 has failed based on the temperature difference between THGO and THG (THGO-THG). In this case, it is erroneously determined that THGO does not indicate the correct temperature immediately before shifting to the operation state in which the supply of the EGR gas should be stopped. However, once the vehicle is stopped, the temperature THG in the EGR passage 12 decreases rapidly, and the temperature THG in the EGR passage 12 immediately after the vehicle starts running is considerably lower than the stored THGO value. Has become. Therefore, the stored T
EGR from temperature difference (THGO-THG) using HGO
If the failure of the control valve 14 is determined, an erroneous determination may occur. Therefore, after the vehicle is stopped, the vehicle speed SPD is 15km
/ H, THGO is set to zero once, and EGO is set until THGO is set in step 403 of FIG.
The failure of the GR control valve 14 is not determined.

Returning to FIG. 12, in step 409, it is determined whether or not the count value CC is 22 seconds or more, as described above, that is, whether or not the vehicle has stopped for 22 seconds or more in the idling operation state. Misfire count value CM is discriminated whether or not greater than a predetermined value CM _o, i.e. the engine speed and EGR gas is being supplied at the time of idling operation varies proceeds to step 410 when the CC ≧ 22sec . Step at the time of the CM ≧ CM _o 4
Proceeding to 11, an abnormality flag X indicating that the EGR control valve 14 has failed is set. Then step 412
For example, during engine operation, the abnormal flag X or the abnormal flag F
(FIG. 8) is set, and then when the engine is operated again after the engine is stopped, when the same abnormality flag X or F is set, it is determined that the EGR control valve 14 has failed. It is turned on.

On the other hand, in step 406, (THGO
When it is determined that (−THG) ≧ ΔT, it is determined that the EGR control valve 14 is operating normally. Therefore, at this time, the routine proceeds to step 413, where the abnormality flag X is reset. Next, at step 414, it is determined whether or not an abnormality flag F (FIG. 8) indicating that the negative pressure control valve 35 has failed is set. When the abnormality flag F is set, the processing cycle is completed. On the other hand, when the abnormality flag F is reset, the routine proceeds to step 415, and when it is determined that the operation is normal during any of the engine operations when the operation and stop of the engine are repeated three times, the warning lamp 58 is turned off. I'm sullen.

FIG. 14 shows a routine for detecting that the EGR control valve 14 is kept closed, and this routine is executed by interruption every predetermined time. Referring to FIG. 4, first, at step 600, it is determined whether or not a detection execution condition for detecting that the EGR control valve 14 is kept closed is satisfied. This detection execution condition indicates when EGR gas is supplied if the EGR control valve 14 is operating normally.
Therefore, it is determined that the detection execution condition is satisfied when the following three conditions are satisfied.

(I) When the throttle opening TA is not less than 5 ° and not more than _Go (FIG. 4). That is, EG in FIG.
When in the R-on region. (Ii) When the engine speed N is higher than 1500 rpm.
If N> 1500 rpm, EGR gas is always supplied. (Iii) When the solenoid 37 of the negative pressure control valve 35 is deenergized.

When it is determined that the detection execution condition is satisfied, the routine proceeds to step 601, and immediately after the detection execution condition is satisfied, the temperature THG in the EGR passage 12 detected by the temperature sensor 52 is set to THGS. Next, the routine proceeds to step 602, where a counter CF indicating the temperature of the EGR passage pipe wall is set to ΔC.
F is added. As the intake air amount Q increases, the supply amount of the EGR gas increases. Therefore, the amount of increase in the temperature of the EGR passage tube wall is proportional to the intake air amount Q. Therefore, the value of ΔCF in step 602 is determined as shown in FIG. It increases as the air amount Q increases. Next, at step 603, it is determined whether or not the count value CF has exceeded the maximum value MAX. When CF ≧ MAX, the routine proceeds to step 604, where C
F is set to MAX. Next, the routine proceeds to step 605.

On the other hand, if it is determined in step 600 that the detection execution condition is not satisfied, then step 60 is executed.
Proceeding to 6, the count value CF is decremented by one. Next, at step 607, it is determined whether or not the count value CF has become equal to or less than zero. When CF ≦ 0, the routine proceeds to step 608, where CF = 0. Then step 65
Proceed to.

Next, at step 605, the count value CF
Is the maximum value MAX. That is, EG
Even when the supply of the R gas is started, the temperature in the EGR passage 12 detected by the temperature sensor 52 does not increase so much while the temperature of the EGR passage tube wall is low. However, CF =
When the temperature becomes MAX, the temperature of the EGR passage tube wall becomes sufficiently high.
The temperature inside becomes higher. Accordingly, if the temperature in the EGR passage 12 is sufficiently high when CF = MAX, the EGR gas has been supplied. If the temperature in the EGR passage 12 is low when CF = MAX, the EGR gas is supplied. Supply has been stopped. Therefore, from the temperature THG in the EGR passage 12 when CF = MAX, the EGR
It can be determined whether or not the control valve 14 is kept closed, and this determination is made in the next steps 607 and 608.

That is, in step 605, CF = MA
If it is determined that the temperature is X, the routine proceeds to step 606, where the temperature TH in the EGR passage 12 detected by the temperature sensor 52
It is determined whether or not G is larger than a value obtained by adding a certain temperature, for example, 30 ° to the intake air temperature THA (THA + 30 °). If THG> THA + 30 ° C., it is considered that the EGR gas has been supplied. Therefore, at this time, the routine proceeds to step 609, where it is determined that the EGR control valve 14 is normal.

On the other hand, when THG ≦ THA + 30 °, it is determined that the supply of the EGR gas may have been stopped, and the routine proceeds to step 607. In step 607, the temperature THG in the EGR passage 12 detected by the temperature sensor 52 is lower than a value (THGS + 10 °) obtained by adding a constant temperature, for example, 10 ° to the temperature THGS in the EGR passage 12 immediately after the detection execution condition is satisfied. It is determined whether or not it is.
When THG <THGS + 10 °, it is considered that the EGR gas was not supplied. Therefore, at this time, the routine proceeds to step 608, where it is determined that the EGR control valve 14 is kept closed. In step 608, the EGR
When it is determined that the control valve 14 remains closed, for example, the warning light 58 is turned on.

[0059]

The fact that the EGR control valve is kept open can be detected in a short time.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a flowchart for controlling a negative pressure control valve.

FIG. 3 is a diagram showing a set value _Qo of an intake air amount.

FIG. 4 is a diagram showing an EGR ON region.

FIG. 5 is a flowchart for controlling a temperature estimation counter.

FIG. 6 is a diagram showing an addition amount ΔXC of a temperature detection count value XC.

FIG. 7 is a diagram showing a change in a temperature detection counter value XC.

FIG. 8 is a flowchart for detecting an opening abnormality of the negative pressure control valve.

FIG. 9 is a graph showing a change in a temperature THG in an EGR passage.

FIG. 10 is a diagram showing a temperature difference ΔT.

FIG. 11 is a flowchart for detecting an abnormal opening of an EGR control valve.

FIG. 12 is a flowchart for detecting an abnormal opening of an EGR control valve.

FIG. 13 is a flowchart for controlling a misfire counter CM.

FIG. 14 is a flowchart for detecting an EGR control valve closing abnormality.

FIG. 15 is a diagram showing an addition value ΔCF of a counter CF.

[Explanation of symbols]

 12 EGR passage 13 EGR controller 14 EGR control valve 15 Modulator 35 Negative pressure control valve 52 Temperature sensor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02M 25/07 550 F02M 25/07 520

Claims (1)

(57) [Claims] A recirculation exhaust gas control valve is disposed in a recirculation exhaust gas passage connecting an engine exhaust passage and an engine intake passage, and the recirculation exhaust gas control is performed in an engine operating state in which exhaust gas is to be recirculated. The temperature in the recirculation exhaust gas passage is detected by an exhaust gas recirculation device that closes the recirculation exhaust gas control valve when the engine is in an operating state in which the valve must be opened and the exhaust gas recirculation should be stopped. And a temperature estimating counter whose count value increases and decreases in accordance with the temperature in the recirculated exhaust gas passage during normal operation of the recirculated exhaust gas valve. When the transition from the operation state to the operation state to stop the exhaust gas recirculation to the operation state to stop the exhaust gas, the temperature in the recirculation exhaust gas passage immediately before the transition and the count value after the transition to a predetermined set value have decreased Diagnosis of an exhaust gas recirculation device which determines that the operation of the recirculation exhaust gas control valve is abnormal when the temperature difference from the temperature in the recirculation exhaust gas passage is smaller than a predetermined temperature difference apparatus.